The most copied StackOverflow snippet of all time is flawed (2019)(programming.guide)
programming.guide
The most copied StackOverflow snippet of all time is flawed (2019)
https://programming.guide/worlds-most-copied-so-snippet.html
350 comments
An idea I've had for a long time is that "the community" can vote to override an accepted answer. There are many times when the accepted answer is incorrect, or a newer answer is now more correct, but the only person who can change an accepted answer is the OP.
I think community-based changes to the accepted answer would go a long way to solving your problem too, but it requires someone to be reviewing newer answers and identifying when there's another that would be more appropriate.
It'd incentivise writing newer answers to older questions. Correcting accepted answers that probably weren't ideal to begin with. A new "role" where users hunt through older questions and answers looking for improvements to make.
Stack Overflow answers are supposed to be community-based, but we unfairly prioritise the will of the original questioner *forever*. I don't think that's optimal.
I think community-based changes to the accepted answer would go a long way to solving your problem too, but it requires someone to be reviewing newer answers and identifying when there's another that would be more appropriate.
It'd incentivise writing newer answers to older questions. Correcting accepted answers that probably weren't ideal to begin with. A new "role" where users hunt through older questions and answers looking for improvements to make.
Stack Overflow answers are supposed to be community-based, but we unfairly prioritise the will of the original questioner *forever*. I don't think that's optimal.
As a side gig I teach an intro to web development class online. Every semester I get students asking for help about why their code isn’t working. Nine times out of ten, they are trying to use some jQuery code they copied from stackoverflow because it is the accepted answer. They don’t yet know enough to recognize that it isn’t vanilla JavaScript (which they are required to use).
The best way to address these students is to ask them "Why do you think that this should work?"
What platform do you use to teach the course? I've been teaching an ML from scratch course for junior devs at my company and think it'd be useful for others.
> but the only person who can change an accepted answer is the OP.
Was it the most efficient? First to answer? Copied-and-pasted right in with no integration work? Written by someone with an Indian username? Got the most upvotes? Made a Simpsons reference? Written by someone with an Anime avatar?
>This system makes the person arguably _least qualified_ to understand the situation the single arbitrator as to which answer is accepted.
Devil's advocate: If it fixed their problem adequately, it's acceptable.
Maybe separate "acceptable" and "ideal" answers would be a nice feature?
Devil's advocate: If it fixed their problem adequately, it's acceptable.
Maybe separate "acceptable" and "ideal" answers would be a nice feature?
In the vast majority of cases, OP did not check (or even define) edge cases, race conditions, memory usage, network activity, etc etc etc.
Seems like the answer is to add a community accepted answer that's easier to change over time, while keeping the accepted answer feature as is.
>This system makes the person arguably _least qualified_ to understand the situation the single arbitrator as to which answer is accepted.
What is the argument for the OP being the least qualified?
What is the argument for the OP being the least qualified?
The argument is probably that while they are the best qualified to know whether it solved their issue, they're not qualified about whether it was the best way to solve their issue, since they had to ask in the first place.
Of all the people involved, he was the one who _didn't_ know how to resolve a specific issue.
Well, they do know the tech stack, the domain, the specific problem. Now they know whether the solution resolved their specific problem, if their code review/testing caught any bugs, etc, etc.
If anything, they have the most amount of information in this context. I really don't think of them as being the least qualified.
If anything, they have the most amount of information in this context. I really don't think of them as being the least qualified.
Yeah there’s an argument for that. I think it’d hold more weight if narrow, specific, and loosely defined duplicate questions were allowed - but they aren’t.
Questions and answers belong to the community. I think the accepted answer should too - maybe after some period of time.
Questions and answers belong to the community. I think the accepted answer should too - maybe after some period of time.
Currently the only incentive to post a new answer to an old question is you get a special badge. That's neat but limited. I've gone through old R questions and posted answers with a more modern syntax and my answers rarely get much attention.
I'd be cautious about overriding an accepted answer. Imagine a situation where there's an easy-to-understand algorithm that's O(n^2) and the "Correct" algorithm that's O(n). If OP only has a dozen datapoints, the former might be the best answer for her specific problem, despite it clearly not being the right approach for most people finding the thread via Google in the future.
I'd be cautious about overriding an accepted answer. Imagine a situation where there's an easy-to-understand algorithm that's O(n^2) and the "Correct" algorithm that's O(n). If OP only has a dozen datapoints, the former might be the best answer for her specific problem, despite it clearly not being the right approach for most people finding the thread via Google in the future.
They actually recently added this feature - you have a "this answer is outdated" button you can press. Note sure what the reputation threshold to see it is.
I've browsed a few tags and haven't been able to see that button and my reputation is 40k+ so I'd expect to have all features enabled.
Are you able to point me to a Meta/Blog post or even just a screenshot please? I'd be keen to see it.
Actually it looks like https://meta.stackoverflow.com/questions/405302/introducing-... is the announcement for wanting to tackle the problem. Not sure if they've implemented it yet though.
Are you able to point me to a Meta/Blog post or even just a screenshot please? I'd be keen to see it.
Actually it looks like https://meta.stackoverflow.com/questions/405302/introducing-... is the announcement for wanting to tackle the problem. Not sure if they've implemented it yet though.
"An idea I've had for a long time is that "the community" can vote to override an accepted answer."
I don't know if this is still a thing, but for some time in the past when an answer was edited more than a certain amount of times it automatically turned into what was called a "community wiki" answer.
I don't know if this is still a thing, but for some time in the past when an answer was edited more than a certain amount of times it automatically turned into what was called a "community wiki" answer.
Or you could just edit the accepted answer if it’s wrong? I’ve seen a few posts where the top contains an “UPDATE” that, in summary, links to another answer.
One of the things that baffles me the most about SO is that I can't sort answers by _newest first_.
If I search for something related to javascript for example, I know there will be a ton of answers for older versions that I am most likely not interested in. However I can only sort by oldest first (related to date).
Old answers are definitely useful a lot of times, but the fact that there's not even the option to sort them the other way around tells me that SO somehow, at it's core, considers new answers less important.
A strange decision if you ask me, considering software changes so much over time.
If anyone has a possible explanation for this I'd love to hear it.
If I search for something related to javascript for example, I know there will be a ton of answers for older versions that I am most likely not interested in. However I can only sort by oldest first (related to date).
Old answers are definitely useful a lot of times, but the fact that there's not even the option to sort them the other way around tells me that SO somehow, at it's core, considers new answers less important.
A strange decision if you ask me, considering software changes so much over time.
If anyone has a possible explanation for this I'd love to hear it.
There are three buttons that act as sorting directions at the top of the answers section: "Votes," "Oldest," and "Active." The "Active" option sorts by most recently modified, which is _usually_ what you'd want instead of strictly newest. (i.e. an edit would update the timestamp, making that answer have a more recent activity date)
So, I guess the answer to your question of "why can't I" is "good news! you can" :)
So, I guess the answer to your question of "why can't I" is "good news! you can" :)
Well, none of those options do what I want.
More often than not, sorting by "Active", "Oldest" and "Votes" usually surface the same 2 or 3 answers, and I still need to scroll down to the bottom to find out the most recently posted answer that has more up to date info.
I don't see why I shouldn't have the choice to sort by "Reverse Oldest" if you will, when it's so useful a lot of the time.
More often than not, sorting by "Active", "Oldest" and "Votes" usually surface the same 2 or 3 answers, and I still need to scroll down to the bottom to find out the most recently posted answer that has more up to date info.
I don't see why I shouldn't have the choice to sort by "Reverse Oldest" if you will, when it's so useful a lot of the time.
This is why Stack Overflow has just started the "Outdated Answers project" in which users can set answers as outdated:
https://meta.stackoverflow.com/questions/405302/introducing-...
I always thought the should have a language version. Eg python3, php7. JavaScript es6....
Tags work to categorize by language (https://stackoverflow.com/questions/tagged/python-3.x); by having multiple languages on one site, you'll have a broader audience because there's few developers that only work with one singular language.
> If I search for something related to javascript for example
As someone that's been learning a little JS over the last year, I quickly came to the realization that you skip over the SO links that come up in the search, and you go to one of the many other sites. I've had good luck with w3schools and mdn. SO is a lost cause for JS.
As someone that's been learning a little JS over the last year, I quickly came to the realization that you skip over the SO links that come up in the search, and you go to one of the many other sites. I've had good luck with w3schools and mdn. SO is a lost cause for JS.
I agree.
However sometimes I am looking for some error related to a botched nodejs install for example, or something that has to do with permissions being set incorrectly and other stuff that does not live in MDN and other documentation sources.
For the actual language questions I do go directly to MDN instead.
However sometimes I am looking for some error related to a botched nodejs install for example, or something that has to do with permissions being set incorrectly and other stuff that does not live in MDN and other documentation sources.
For the actual language questions I do go directly to MDN instead.
> we should look at the number of votes, divided by the number of views
Closer, but still not quite what you want probably or a few stray votes can make a massive impact just from discretization effects. What you really care about is which answer is "best" by some metric, and you're trying to infer that as best as possible from the voting history. Average votes do a poor job. Check out this overview from the interblags [0].
[0] https://www.evanmiller.org/how-not-to-sort-by-average-rating...
Closer, but still not quite what you want probably or a few stray votes can make a massive impact just from discretization effects. What you really care about is which answer is "best" by some metric, and you're trying to infer that as best as possible from the voting history. Average votes do a poor job. Check out this overview from the interblags [0].
[0] https://www.evanmiller.org/how-not-to-sort-by-average-rating...
This isn't just a statistical problem, it's also a classical exploration/exploitation trade-off. You want users to notice and vote on new answers (exploration), but users only want to see the best answers (exploitation). The order you show will influence future votes (and future answers).
In addition, it's a social engineering problem. At least people with a western psychology seem to respond very strongly when a score is attributed to their person (as opposed to a group success like in a wiki). So you better make the score personal and big and visible, and do not occasionally sort by random just to discover the true score.
In addition, it's a social engineering problem. At least people with a western psychology seem to respond very strongly when a score is attributed to their person (as opposed to a group success like in a wiki). So you better make the score personal and big and visible, and do not occasionally sort by random just to discover the true score.
I think that's a great example of the "smoothing" that I was alluding to, though not in a format accessible to most programmers. However it is still just using a function of upvotes and downvotes. I think true rating can be much better when you also incorporate number of opportunities to vote. Because having the opportunity to vote (by viewing an item, or purchasing it, or whatnot) and choosing not to vote is still a really useful piece of data about the quality of an item. Especially when you are comparing old items that have had millions of opportunities against new items with only thousands.
> number of opportunities
Yep, definitely. The only challenges there are that there's less literature about doing so and that if you have both up and down votes there's no longer one right way to define a single objective for scoring.
Yep, definitely. The only challenges there are that there's less literature about doing so and that if you have both up and down votes there's no longer one right way to define a single objective for scoring.
> I think this shows an example of a big problem with StackOverflow compared to its initial vision. I remember listening to Jeff and Joel's podcast, and hearing the vision of applying the Wikipedia model to tech Q&A. The idea was that answers would continue to improve over time.
Interessting. As a random visitor this was something that never came to me from the way SO presents itself.
> For the most part, they don't. I'm not quite sure if it's an issue of incentives or culture.
I think it's more a problem of communication and UI. SO is not really the kind of site that animates people to answer or improve things. The overall design is also more technical and strange, not motivating and userfriendly.
Today for the first time I realized that there is a history for answers and an "improve"-Button that seems to allow me to change someone else answer. I only saw that because I expliciet looked for this because of this thread.
Wikipedia in the beginning was very vocal and motivating to engage all kind people to help and improve articles. SO never had that vibes for me. Additionally, it simply has not the interface that makes it simple to do this stuff. There are only this aweful comments under each answer, which are not really useful to discus an answer in all lenght and from all sides. Might be better to change them to a full fletched forum with some kollaboration editing and some small wiki-functionality or something like that.
I remember they tried to do some kind of wiki with high quality-code-parts, what happend to that?
Interessting. As a random visitor this was something that never came to me from the way SO presents itself.
> For the most part, they don't. I'm not quite sure if it's an issue of incentives or culture.
I think it's more a problem of communication and UI. SO is not really the kind of site that animates people to answer or improve things. The overall design is also more technical and strange, not motivating and userfriendly.
Today for the first time I realized that there is a history for answers and an "improve"-Button that seems to allow me to change someone else answer. I only saw that because I expliciet looked for this because of this thread.
Wikipedia in the beginning was very vocal and motivating to engage all kind people to help and improve articles. SO never had that vibes for me. Additionally, it simply has not the interface that makes it simple to do this stuff. There are only this aweful comments under each answer, which are not really useful to discus an answer in all lenght and from all sides. Might be better to change them to a full fletched forum with some kollaboration editing and some small wiki-functionality or something like that.
I remember they tried to do some kind of wiki with high quality-code-parts, what happend to that?
One of the really frustrating things about SO is that once you reach a certain rep threshold, you lose the ability to suggest edits, and instead gain the ability to just make the edits directly. I'm a lot more likely to do the former, because it helps ensure that if I actually made a mistake, it will be caught by the people voting on it. And so SO has lost out on a bunch of my suggested edits because they took away my ability to suggest edits.
What would really help with the vision here is some way to comment and associate tests against posted code. I have corrected algorithms on Wikipedia that were obviously wrong with even a cursory test. Then people can adjust the snippet, debate the test parameters, or whatever else they need to do while maintaining some sort of sanity check. If it’s good enough for random software projects used by a dozen people, it’s probably good enough for snippets used by thousands of developers and even more users.
This post made me think the same thing. It would be nice to have a StackOverflow that was actually more code focused. People could write tests or code and actually run them.
I always try and improve existing answers with edits. Often just adding important context when the answer is just a line of bash and adding links to source documentation.
There's very little gamification incentive to do so and often the edit queue is full. Still, there are lots of times where important caveats and information is pointed out in the comments and never added to the answer
There's very little gamification incentive to do so and often the edit queue is full. Still, there are lots of times where important caveats and information is pointed out in the comments and never added to the answer
The other day I asked a question about the c/c++ plugin of vscode, somebody swooped in to edit it to just be c++ because “c/c++ is not a programming language”. The question wasn’t answered. I wonder what’s the incentive for people to do something like that.
> As a result, other people don't feel enabled to come along and tweak the answer to improve it.
It's worse than that. Edits have to go through a review process that is much more selective and often arbirarily rejects good edits.
It's worse than that. Edits have to go through a review process that is much more selective and often arbirarily rejects good edits.
Only if you're a low rep user, though. And no, many more bad edits are accepted, than good edits being rejected. By orders of magnitude.
> Only if you're a low rep user, though.
What qualifies as "low rep"? I'm easily in the too quintile.
> And no, many more bad edits are accepted, than good edits being rejected. By orders of magnitude.
Do you have any data to support this?
The editing and updating process for stackoverflow is broken and as a direct result I've used the site less and less over the years. Denying the problem just hastens the demise of the site.
What qualifies as "low rep"? I'm easily in the too quintile.
> And no, many more bad edits are accepted, than good edits being rejected. By orders of magnitude.
Do you have any data to support this?
The editing and updating process for stackoverflow is broken and as a direct result I've used the site less and less over the years. Denying the problem just hastens the demise of the site.
Editing answers is a complete waste of time. You can post a correction along with a copy and paste of the relevant section from the documentation, yet have your edit disappear without explanation.
To correctly measure the quality of an item one needs to take something like Google's PageRank algorithm and apply it to people. That is, there needs to be some measure of the reputation of the person posting. This doesn't mean that a person who was correct in the past is necessarily correct right now, but it is true that people who are often correct tend to go on being correct, and people who are often wrong tend to go on being wrong. Careful people tend to continue to be careful, and sloppy people tend to continue to be sloppy. It's important to capture that reality and use it as a weight given to any particular answer.
Potentially a stupid question; why is it not possible to just make a MediaWiki site explicitly for SO questions? Does it exist already?
The technical cost/effort for someone like you or me to do that is minimal. The expensive part is the ongoing social maintenance fee aka moderation. As evident by the stack overflow drama re: Monica, it’s an unsolved (non-technical) problem that you could make your own mint to print money on, if you were able to fix any tiny part of it.
And then we would run again into people with an inflated ego, edit wars etc.
The Monica situation is probably a bad example; that was Stack Overflow (the company) royally and unilaterally messing up. It's certainly not a usual situation for resource-curating communities.
I've written, and deleted, several essays on the matter, but a TL;DR: Monica's legitimate questions to staff about a policy got caught up in a crackdown on sealioning-type harassment of trans (etc.) mods in the mod chat, and SO management basically declared war on Monica by mistake. We don't know whether they dealt with the actual harassment (though I think they did, belatedly), because if they did, proper procedure was followed and the perps weren't named-and-shamed in the press.
I've written, and deleted, several essays on the matter, but a TL;DR: Monica's legitimate questions to staff about a policy got caught up in a crackdown on sealioning-type harassment of trans (etc.) mods in the mod chat, and SO management basically declared war on Monica by mistake. We don't know whether they dealt with the actual harassment (though I think they did, belatedly), because if they did, proper procedure was followed and the perps weren't named-and-shamed in the press.
Wouldn't a simple TTL - Time to live, solve that problem, of course with an option to see the graveyard.
This would mean that the same questions would get answered again and again over the years, but I think that could also solve the negative reputation problem of the website.
Two bird with one stone, or if you're Slovenian, two flies with one swat. ^^
This would mean that the same questions would get answered again and again over the years, but I think that could also solve the negative reputation problem of the website.
Two bird with one stone, or if you're Slovenian, two flies with one swat. ^^
For anyone else that is curious like I was, the #6 answer on that list is from 12 years ago: https://stackoverflow.com/a/140861/
>> For the most part, they don't. I'm not quite sure if it's an issue of incentives or culture.
Classic example of "good is the enemy of best".
Classic example of "good is the enemy of best".
What’s wrong with a simple loop (like the one near the top)? Why does it have to branchless? Wouldn’t the IO take longer than missed branches/pipeline flushes?
Not to mention that the fixed version now has branches as well…
Not to mention that the fixed version now has branches as well…
Not sure why some programmers these days have aversion to simple loops and other boring - but readable - code.
Instead we have overused lambdas and other tricks that started out clever but become a nightmare when wielded without prudence. In this article, the author even points out why not to use his code:
Note that this started out as a challenge to avoid loops and excessive branching. After ironing out all corner cases the code is even less readable than the original version. Personally I would not copy this snippet into production code.
Instead we have overused lambdas and other tricks that started out clever but become a nightmare when wielded without prudence. In this article, the author even points out why not to use his code:
Note that this started out as a challenge to avoid loops and excessive branching. After ironing out all corner cases the code is even less readable than the original version. Personally I would not copy this snippet into production code.
I'm not against using for loops when what you need is an actual loop.
The thing is most of the times, previously, for loops where actually doing something for which there are concepts that express exactly what was being done - though not in all languages.
For instance, map - I know that it will return a new collection of exactly the same number of items the iterable being iterated has. When used correctly it shouldn't produce any side-effects outside the mapping of each element.
In some languages now you have for x in y which in my opinion is quite ok as well, but still to change the collection it has to mutate it, and it's not immediate what it will do.
If I see a reduce I know it will iterate again a definite number of times, and that it will return something else than the original iterable (usually), reducing a given collection into something else.
On the other hand forEach should tell me that we're only interested in side-effects.
When these things are used with their semantic context in mind, it becomes slightly easier to grasp immediately what is the scope of what they're doing.
On the other hand, with a for (especially the common, old school one) loop you really never know.
I also don't understand what is complex about the functional counterparts - for (initialise_var, condition, post/pre action) can only be simpler in my mind due to familiarity as it can have a lot of small nuances that impact how the iteration goes - although to be honest, most of the times it isn't complex either - but does seem slightly more complex and with less contextual information about the intent behind the code.
For instance, map - I know that it will return a new collection of exactly the same number of items the iterable being iterated has. When used correctly it shouldn't produce any side-effects outside the mapping of each element.
In some languages now you have for x in y which in my opinion is quite ok as well, but still to change the collection it has to mutate it, and it's not immediate what it will do.
If I see a reduce I know it will iterate again a definite number of times, and that it will return something else than the original iterable (usually), reducing a given collection into something else.
On the other hand forEach should tell me that we're only interested in side-effects.
When these things are used with their semantic context in mind, it becomes slightly easier to grasp immediately what is the scope of what they're doing.
On the other hand, with a for (especially the common, old school one) loop you really never know.
I also don't understand what is complex about the functional counterparts - for (initialise_var, condition, post/pre action) can only be simpler in my mind due to familiarity as it can have a lot of small nuances that impact how the iteration goes - although to be honest, most of the times it isn't complex either - but does seem slightly more complex and with less contextual information about the intent behind the code.
For me, code with reduce is less readable than a loop. With loop everything is obvious, but with reduce you need to know what arguments in a callback mean (I don't remember), and then think how the data are transformed. It's an awful choice in my opinion. Good old loop is so much better.
I disagree entirely. In most imperative programming languages, you can shove any sort of logic inside a loop, more loops, more branches, creating new objects, its all fair game.
Fold and map in functional languages are often much more restrictive in a sense. For example, with lists, you reduce down a collection [a]->a to a single object, or produce another collection with a map [a]->[a]. So map and fold etc are much more restrictive. That's what makes it clearer.
Fold and map in functional languages are often much more restrictive in a sense. For example, with lists, you reduce down a collection [a]->a to a single object, or produce another collection with a map [a]->[a]. So map and fold etc are much more restrictive. That's what makes it clearer.
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if you are used to imperative programming, then yes.
But in a for loop anything can happen- from a map to a reduce to a mix, to whatever convoluted logic the dev comes up with.
But in a for loop anything can happen- from a map to a reduce to a mix, to whatever convoluted logic the dev comes up with.
Technically you can implement map as reduce ;)
But yes - for me
If the operation is conceptually accumulating something over the whole collection and if it's idiomatic in the language I'm using - I will use reduce. Same with map-y and filter-y operations.
But if I have to do some mental gymnastics to make the operation fit reduce - for loop it is. Or generator expression in case of python.
But yes - for me
(defn factorial [n]
(reduce * (range 1 (inc n))))
def factorial(n):
result = 1
for i in range(2,n+1):
result *= i
return result
If the operation is conceptually accumulating something over the whole collection and if it's idiomatic in the language I'm using - I will use reduce. Same with map-y and filter-y operations.
But if I have to do some mental gymnastics to make the operation fit reduce - for loop it is. Or generator expression in case of python.
Indeed. I rarely encounter basic loops in code reviews now, so seeing one is definitely a small alert to do an extra thorough review of that part.
And it is usually very easy and straightforward to see what is going on inside.
It can definitively happen, but I think more times than not the others are more readable.
To be honest this seems to be a familiarity thing > but with reduce you need to know what arguments in a callback mean
If I didn't know for it would be mind boggling what those 3 things, separated by semicolons, are doing It doesn't look like anything in the usual language(s) they're implemented. It's the same with switch.
The only thing both of them have, for and switch, and helps, is that languages that offer it and aren't FP usually use the same *C* form across all, whereas reduce's args and the callback args vary a bit more between languages, and specially between mutable and immutable langs.
I still prefer most of the time the functional specific counterparts.
To be honest this seems to be a familiarity thing > but with reduce you need to know what arguments in a callback mean
If I didn't know for it would be mind boggling what those 3 things, separated by semicolons, are doing It doesn't look like anything in the usual language(s) they're implemented. It's the same with switch.
The only thing both of them have, for and switch, and helps, is that languages that offer it and aren't FP usually use the same *C* form across all, whereas reduce's args and the callback args vary a bit more between languages, and specially between mutable and immutable langs.
I still prefer most of the time the functional specific counterparts.
Guido?
When used correctly it shouldn't produce any side-effects outside the mapping of each element.
But that's just a social convention. There's nothing stopping you from doing other things during your map or reduce.
In practice, the only difference between Map, Reduce and a For loop is that the first two return things. So depending on whether you want to end up with an array containing one item for each pass through the loop, "something else", or nothing, you'll use Map, Reduce or forEach.
You can still increment your global counters, launch the missiles or cause any side effects you like. "using it correctly" and not doing that is just a convention that you happen to prefer.
But that's just a social convention. There's nothing stopping you from doing other things during your map or reduce.
In practice, the only difference between Map, Reduce and a For loop is that the first two return things. So depending on whether you want to end up with an array containing one item for each pass through the loop, "something else", or nothing, you'll use Map, Reduce or forEach.
You can still increment your global counters, launch the missiles or cause any side effects you like. "using it correctly" and not doing that is just a convention that you happen to prefer.
That is true (less so in FP languages though), but the for loop doesn't either - indeed I do prefer it most of the times, I think its a reasonable expectation to provide the most intention revealing constructs when possible, it's also easier to spot "code smells" when using those.
The exceptions I make is when there's significant speed concerns/gains, when what you're doing is an actual loop, when the readability by using a loop is improved.
(and I haven't read the article so not even sure I agree with the example there, this was more in general terms)
(and I haven't read the article so not even sure I agree with the example there, this was more in general terms)
Yeah, I'd much rather have something like
Same one-liner in (slightly uglier) Python:
congruence_classes m l = map (\x -> ((x ==) . (`mod` m)) l) [0..m-1]
def congruence_classes(m, l):
sets = []
for i in range(m):
sets += [[]]
for v in l:
sets[v % m] += [v]
return sets
Same one-liner in (slightly uglier) Python:
def congruent_sets(m, l):
return list(map(lambda x: list(filter(lambda v: v % m == x, l)), range(m)))The one liner is far less readable and under the hood it actually is worse: for each value in [0, m] you're iterating l and filtering it, so it's a O(n^2) code now instead of O(n). That mistake would be far easier to notice if you had written the exact same algorithm with loops: one would see a loop inside a loop and O(n^2) alarms should be ringing already.
Ironically, it's a great example of why readability is so much more important than conciseness and one liners.
Ironically, it's a great example of why readability is so much more important than conciseness and one liners.
I agree and despite beeing a fan (kind of a convert from OO) of FP I am often wondering about readability of FP code.
One idea I have is, that often FP code is not modularized and violates the SOLID principle in doing several things in one line.
there are seldom named subfunctions where the name describe the purpose of the functions- take lamdas as an example: I have to parse the lamda code to learn what it does. Even simple filtering might be improved (kinda C#):
var e = l.Filter(e => e.StartsWith("Comment"));
vs.
var e = l.Filter(ElementIsAComment);
or even using an extension method:
var e = l.FindComments();
sorry I could not come up with a better example- I hope you get my point...
One idea I have is, that often FP code is not modularized and violates the SOLID principle in doing several things in one line.
there are seldom named subfunctions where the name describe the purpose of the functions- take lamdas as an example: I have to parse the lamda code to learn what it does. Even simple filtering might be improved (kinda C#):
var e = l.Filter(e => e.StartsWith("Comment"));
vs.
var e = l.Filter(ElementIsAComment);
or even using an extension method:
var e = l.FindComments();
sorry I could not come up with a better example- I hope you get my point...
True, it is computationally worse, though it's O(nm) so applying m at compile time to form a practical use as I used it will turn it into to O(n) in practice.
But that much is immediately obvious since it's mapping a filter, that is, has a loop within a loop.
I did consider the second one to also take quadratic time though. I forgot that in python getting list elements by index is O(1) instead of O(n) which is what I'm personally used to with lists.
It's also true that you can replace the filter with
(x ==) . (`mod` m)
I just love how it looks and it doesn't personally seem any less clear to me, maybe a bit more verbose.
But that much is immediately obvious since it's mapping a filter, that is, has a loop within a loop.
I did consider the second one to also take quadratic time though. I forgot that in python getting list elements by index is O(1) instead of O(n) which is what I'm personally used to with lists.
It's also true that you can replace the filter with
[ v | v <- l, v `mod` m == x ]
(x ==) . (`mod` m)
I just love how it looks and it doesn't personally seem any less clear to me, maybe a bit more verbose.
"I forgot that in python getting list elements by index is O(1) instead of O(n) which is what I'm personally used to with lists."
Have you considered that maybe this is a sign you're too deep into using impractical programming languages?
Cleanness for immutable data structures aside, linked list are a very poor way to store data given the way computer architectures are designed.
Have you considered that maybe this is a sign you're too deep into using impractical programming languages?
Cleanness for immutable data structures aside, linked list are a very poor way to store data given the way computer architectures are designed.
> Have you considered that maybe this is a sign you're too deep into using impractical programming languages?
“Languages that use ‘list’ for linked lists and have different names for other integer-indexable ordered collections” aren’t necessarily “impractical”.
“Languages that use ‘list’ for linked lists and have different names for other integer-indexable ordered collections” aren’t necessarily “impractical”.
> True, it is computationally worse, though it's O(nm) so applying m at compile time to form a practical use as I used it will turn it into to O(n) in practice.
Even applying it at compile time, it's still O(nm). You have to compute 'v mod m' for each possible value of v and m.
> But that much is immediately obvious since it's mapping a filter, that is, has a loop within a loop.
It's not immediately obvious because you have to parse the calls and see exactly where is the filter and the map.
> I just love how it looks and it doesn't personally seem any less clear to me, maybe a bit more verbose.
It doesn't seem any less clear to you because you're used to it. But think about the things you need to know apart from what a loop, map, filters and lambdas are:
- What is (x ==). Is it a function that returns whether the argument is equal to x? - What is '.'. Function composition? Filter? - Same thing with `mod` m. What are the backticks for?
Compare that with the amount of things you need to know with the Python code with for loops. For that complexity to pay off you need some benefits, and in this case you're only getting disadvantages.
That's the whole point of this discussion. Production code needs to work, have enough performance for its purpose and be maintainable, those are the metrics that matter. Being smart, beautiful or concise are completely secondary, and focusing on them will make for worse code, and it's exactly what happened in this toy example.
Even applying it at compile time, it's still O(nm). You have to compute 'v mod m' for each possible value of v and m.
> But that much is immediately obvious since it's mapping a filter, that is, has a loop within a loop.
It's not immediately obvious because you have to parse the calls and see exactly where is the filter and the map.
map(lambda x: do_some_things(x, another_param), filter(lambda x: filter_things(x), lst))
map(lambda x: do_some_things(x, filter(lambda y: filter_things(x, y), another_list)), range(m))
retval = []
for x in lst:
if not filter_things(x):
continue
retval.append(do_some_things(x))
for x in lst:
filtered = []
for y in in another_list:
if filter_things(x, y):
filtered.append(y)
retval.append(do_some_things(x, filtered))
> I just love how it looks and it doesn't personally seem any less clear to me, maybe a bit more verbose.
It doesn't seem any less clear to you because you're used to it. But think about the things you need to know apart from what a loop, map, filters and lambdas are:
- What is (x ==). Is it a function that returns whether the argument is equal to x? - What is '.'. Function composition? Filter? - Same thing with `mod` m. What are the backticks for?
Compare that with the amount of things you need to know with the Python code with for loops. For that complexity to pay off you need some benefits, and in this case you're only getting disadvantages.
That's the whole point of this discussion. Production code needs to work, have enough performance for its purpose and be maintainable, those are the metrics that matter. Being smart, beautiful or concise are completely secondary, and focusing on them will make for worse code, and it's exactly what happened in this toy example.
Why not just use a list comprehension?
def congruent_sets(m, l):
return [[v for v in l if v % m == i] for i in range(m)]Isn't that unnecessary quadratic algorithm (nested loops, m*l iterations, instead of m + l)?
Yes, but that's the case with all the functional approaches proposed.
If Python were focused on functional programming it would have a utility function for this similar to itertools.groupby (but with indices in an array instead of keys in a dictionary).
If Python were focused on functional programming it would have a utility function for this similar to itertools.groupby (but with indices in an array instead of keys in a dictionary).
> If Python were focused on functional programming it would have a utility function for this similar to itertools.groupby (but with indices in an array instead of keys in a dictionary).
itertools.groupby doesn’t return a dictionary, it returns an iterator of (key, (iterator that produces values)) tuples. It sounds, though, like you want something like:
itertools.groupby doesn’t return a dictionary, it returns an iterator of (key, (iterator that produces values)) tuples. It sounds, though, like you want something like:
from itertools import groupby
def categorize_into_list(source, _range, key):
first = lambda x: x[0]
sublist_dict = {
k: list(v[1] for v in vs)
for k, vs in groupby(sorted(((key(v), v) for v in source), key=first), first))
}
return [sublist_dict.get(i, []) for i in _range]
def congruent_sets(m, l):
categorize_into_list(l, m, lambda v: v % m)Yeah exactly.
> For instance, map - I know that it will return a new collection of exactly the same number of items the iterable being iterated has.
Unless you're using Perl - "Each element of LIST may produce zero, one, or more elements in the generated list".
Unless you're using Perl - "Each element of LIST may produce zero, one, or more elements in the generated list".
Perl implements flatMap and calls it map :-)
I can't comment on the social phenomenon here, but there is indeed a decent technical argument for avoiding for loops when possible.
In a nutshell, it's kind of like "prinicple of least priviledge" applied to loops. Maps are weaker than Folds which are weaker than For loops, meaning that the stronger ones can implement the weaker ones but not vice-versa. So it makes sense to choose the weakest version.
More specifically, maps can be trivially parallelized; same for folds, but to a lesser degree, if the reducing operation is associative; and for-loops are hard.
In a way, the APL/J/K family takes this idea and explores it in fine detail. IMHO, for loops are "boring and readable" but only in isolation; when you look at the system as a whole lots of for loops make reasoning about the global behaviour of your code a lot harder for the simple reasone that for-loops are too "strong", giving them unweildy algebraic properties.
In a nutshell, it's kind of like "prinicple of least priviledge" applied to loops. Maps are weaker than Folds which are weaker than For loops, meaning that the stronger ones can implement the weaker ones but not vice-versa. So it makes sense to choose the weakest version.
More specifically, maps can be trivially parallelized; same for folds, but to a lesser degree, if the reducing operation is associative; and for-loops are hard.
In a way, the APL/J/K family takes this idea and explores it in fine detail. IMHO, for loops are "boring and readable" but only in isolation; when you look at the system as a whole lots of for loops make reasoning about the global behaviour of your code a lot harder for the simple reasone that for-loops are too "strong", giving them unweildy algebraic properties.
While these are all valid and well thought out arguments, in this particular example, a whole class of problems and bugs were introduced specifically by avoiding simple loops.
Not to mention the performance implications. Parallelisation, composability and system thinking are sometimes overkill and lead to overengineering.
Not to mention the performance implications. Parallelisation, composability and system thinking are sometimes overkill and lead to overengineering.
> So it makes sense to choose the weakest version.
Only if it's actually more readable. The principle of least privilege does not give you any benefit when talking about loop implementations.
> More specifically, maps can be trivially parallelized;
This argument is repeated time and time again but I've never actually seen it work. Maps that can be trivially parallelized aren't worthy to parallelize most of the time. In the rare case it's both trivial and worthy, it's because the map function (and therefore the loop body) are side-effect free, and for those rare cases you don't care too much about the slightly extra effort of extracting the loop body into a function.
> when you look at the system as a whole lots of for loops make reasoning about the global behaviour of your code a lot harder for the simple reason that for-loops are too "strong"
Code is too strong in general. Reasoning about the global behavior of code is difficult if the code itself is complex. Nested maps and reduces will be equally difficult to comprehend. The fact that a map() function tells you that you're converting elements of lists does not save you from understanding what is that conversion doing and why.
Sometimes loops will be better for readability, sometimes it will be map/reduce. Saying that for loops always make it harder to reason about the code does not make too much sense in my opinion.
Only if it's actually more readable. The principle of least privilege does not give you any benefit when talking about loop implementations.
> More specifically, maps can be trivially parallelized;
This argument is repeated time and time again but I've never actually seen it work. Maps that can be trivially parallelized aren't worthy to parallelize most of the time. In the rare case it's both trivial and worthy, it's because the map function (and therefore the loop body) are side-effect free, and for those rare cases you don't care too much about the slightly extra effort of extracting the loop body into a function.
> when you look at the system as a whole lots of for loops make reasoning about the global behaviour of your code a lot harder for the simple reason that for-loops are too "strong"
Code is too strong in general. Reasoning about the global behavior of code is difficult if the code itself is complex. Nested maps and reduces will be equally difficult to comprehend. The fact that a map() function tells you that you're converting elements of lists does not save you from understanding what is that conversion doing and why.
Sometimes loops will be better for readability, sometimes it will be map/reduce. Saying that for loops always make it harder to reason about the code does not make too much sense in my opinion.
I agree with the no silver bullet thing - and written on another reply I don't even know if I agree with the example in the article.
> The fact that a map() function tells you that you're converting elements of lists does not save you from understanding what is that conversion doing and why.
It can actually, say you have a query that comes in, this calls a function that fetches records from the database, it's not a basic query, it has joins, perhaps a subquery, etc. Then you have another function that transforms the results into whatever presentational format, decorates, wtv, those results, and it's also more than a few basic couple lines of logic.
And now you have a bug report come in, that not all expected results are being shown.
If you have
If you have
> The fact that a map() function tells you that you're converting elements of lists does not save you from understanding what is that conversion doing and why.
It can actually, say you have a query that comes in, this calls a function that fetches records from the database, it's not a basic query, it has joins, perhaps a subquery, etc. Then you have another function that transforms the results into whatever presentational format, decorates, wtv, those results, and it's also more than a few basic couple lines of logic.
And now you have a bug report come in, that not all expected results are being shown.
If you have
func does_query -> loop transforms
If you have
func does_query -> func maps_results
Loops are easier to read. With functions like reduce you have to solve a puzzle every time to understand what the code is doing (this is also true for functional style of programming in general).
> More specifically, maps can be trivially parallelized; same for folds, but to a lesser degree, if the reducing operation is associative; and for-loops are hard.
In a typical Javascript code reduce operation will not be parallelized. It actually can be slower than a loop because of overhead for creating and calling a function on every iteration.
> when you look at the system as a whole lots of for loops
A code with lot of loops is still more readable than a code with lots of nested reduces.
> More specifically, maps can be trivially parallelized; same for folds, but to a lesser degree, if the reducing operation is associative; and for-loops are hard.
In a typical Javascript code reduce operation will not be parallelized. It actually can be slower than a loop because of overhead for creating and calling a function on every iteration.
> when you look at the system as a whole lots of for loops
A code with lot of loops is still more readable than a code with lots of nested reduces.
>Loops are easier to read. With functions like reduce you have to solve a puzzle every time to understand what the code is doing
I think that is a function of familiarity, if you use reduce a lot it will be as easy to read as a loop - perhaps easier because more compact - there is a downside to reading more lines for some people, at some point verbosity becomes its own source of illegibility (although any loop that can easily be turned into a reduce probably won't be excessively verbose anyway)
Of course all that is just on the personal level, you , by using and reading more code with reduce in it will stop finding reduce less easy to understand than loops - but the next programmer without lots of reduce experience will be in your same boat.
I think that is a function of familiarity, if you use reduce a lot it will be as easy to read as a loop - perhaps easier because more compact - there is a downside to reading more lines for some people, at some point verbosity becomes its own source of illegibility (although any loop that can easily be turned into a reduce probably won't be excessively verbose anyway)
Of course all that is just on the personal level, you , by using and reading more code with reduce in it will stop finding reduce less easy to understand than loops - but the next programmer without lots of reduce experience will be in your same boat.
I disagree quite strongly, in that this is simply a function of familiarity. Reduce is no more or less readable than for (especially the C style for — imagine trying to work out what the three not-really-arguments represent!)
loops are harder to read. What does it do, map, reduce, send emails to grandma?
In JavaScript, the reduce callback is created once and called repeatedly. For loops are pretty much always the fastest possible way because they use mutable state. They are also a really good way of creating unreadable spaghetti that does things you don't want them to.
I'm not sure what you mean by nested reduces. Chained reduce functions are easy to follow
In JavaScript, the reduce callback is created once and called repeatedly. For loops are pretty much always the fastest possible way because they use mutable state. They are also a really good way of creating unreadable spaghetti that does things you don't want them to.
I'm not sure what you mean by nested reduces. Chained reduce functions are easy to follow
You can send email to grandma from both map and reduce.
The point was that in map and reduce it's clear what's being done and what's being returned, especially in a typed language. Ideally you're also in an environment that doesn't allow for side effects, in which case, grandma gets no emails from map or reduce
It is not visible what is returned or what is input im case of chaining. Because return and input parameters are not directly visible and you have to read all previous calls to figure that out.
And they both trivially allow for side effects.
And they both trivially allow for side effects.
Very often processes are naturally modelled as a series of transformations. In those cases, writing manual loops is tedious, error-prone, harder to understand, less composable and potentially less efficient (depending on language and available tools) than using some combination of map, filter and reduce.
> Not sure why some programmers these days have aversion to simple loops and other boring - but readable - code.
Like goto, basic loops are powerful, simple constructs that tell you nothing at all about what the code is doing. For…in loops in many languages are a little better, but map, reduce, or comprehensions are much more expressive as to what the code is doing, but mostly address common cases of for loops.
While loops are weakly expressive (about equal to for…in), but except where they are used as a way (in language without C-style for loops) but there is less often a convenient replacement.
Like goto, basic loops are powerful, simple constructs that tell you nothing at all about what the code is doing. For…in loops in many languages are a little better, but map, reduce, or comprehensions are much more expressive as to what the code is doing, but mostly address common cases of for loops.
While loops are weakly expressive (about equal to for…in), but except where they are used as a way (in language without C-style for loops) but there is less often a convenient replacement.
Disclamer: amateur developer for 25 years, no formal education in that area
a loop that iterates over indices when I want elements is not readable, e.g. I prefer
a loop that iterates over indices when I want elements is not readable, e.g. I prefer
for element in elements:
for (i = 0 , i < len(elements), i++) { element = elements[i] ...
I find that many times in more complex loops you need the index as well. Sometimes for as mundane reason as logging.
Yes, my code is not that complicated and I use languages that are rather high level (Python, Golang, JS with Vue) so I needed the index I think once when I had to remove an element from an array in JS and for some reason I was not using lodash.
But yes, there are of course cases where the index could be needed, I was merely commenting on the aversion part for generic developers.
But yes, there are of course cases where the index could be needed, I was merely commenting on the aversion part for generic developers.
Yes, this plagues JDK8+ code. Every fashionable Java coder has to use an overly complex, lazy stream vs a simple loop in every case.
The irony is that a single log computation is going to take longer than the loop. (No idea if implementing a log approximation involves loops either.)
https://code.woboq.org/userspace/glibc/sysdeps/ieee754/dbl-6...
I don't see any loops, but there are a number of branches. The code could probably be generalized using loops to support arbitrary precision, but I think any optimized implementation for a specific precision will have unrolled them.
I don't see any loops, but there are a number of branches. The code could probably be generalized using loops to support arbitrary precision, but I think any optimized implementation for a specific precision will have unrolled them.
Sounds like textbook example of when theory is misaligned with reality.
Waiting for someone to post some fast-inverse-sqrt-esque hack to compute the logarithm. Although in Java that's probably not likely to be faster.
I wonder how fast it'd be to convert to string and count digits.
I wonder how fast it'd be to convert to string and count digits.
> I wonder how fast it'd be to convert to string and count digits.
When you convert the number to a string you're really transforming it to a decimal format. Which is the domain where you should be solving the problem. Otherwise you're doing some sort transformation in the binary domain and then hopping to pull the answer out of a hat when you do the final convertion to decimal.
When you convert the number to a string you're really transforming it to a decimal format. Which is the domain where you should be solving the problem. Otherwise you're doing some sort transformation in the binary domain and then hopping to pull the answer out of a hat when you do the final convertion to decimal.
Many architectures include a logarithm instruction. Does Java use that if available? Would it make a difference?
Many architectures? What would they be?
Regardless whether they contain a logarithm instruction or not, how may architectures are there these days. Outside of truly embedded computing I can only come up with 2: Intel and ARM. Counting POWER and RISCV is probably a bit of a stretch already.
Regardless whether they contain a logarithm instruction or not, how may architectures are there these days. Outside of truly embedded computing I can only come up with 2: Intel and ARM. Counting POWER and RISCV is probably a bit of a stretch already.
x86 has two logarithm instructions, FYL2X and FYL2XP1.
FYL2X takes two arguments, Y and X, and computes Y log2(X).
FYL2XP1 takes two arguments, Y and X, and computes Y log2(X+1).
As you note, x86 and ARM are by far the most used, and I'd guess that when it comes to Java you are more likely to be running on x86 than ARM, so I figured it was arguable to say "many" when the only one I was sure had a logarithm instruction was x86.
FYL2X takes two arguments, Y and X, and computes Y log2(X).
FYL2XP1 takes two arguments, Y and X, and computes Y log2(X+1).
As you note, x86 and ARM are by far the most used, and I'd guess that when it comes to Java you are more likely to be running on x86 than ARM, so I figured it was arguable to say "many" when the only one I was sure had a logarithm instruction was x86.
Those x86 instructions are “legacy floating point” instructions. As in, the x87 FPU. Benchmarks I’ve seen seem to indicate that the x87 “coprocessor” is slow compared to the SSE/AVX FPUs, and only exists for backwards compatibility. I don’t think SSE/AVX has a logarithm instruction, sadly, but there are intrinsics for them: `_mm256_log_pd` for example. Considering that intrinsic generates a “sequence” instead of a single instruction, I’d be curious how it compares to x87.
[deleted]
Besides log()'s implementation is certainly not branch-less.
It's the ostrich approach: if you don't see the branches they don't matter.
It's the ostrich approach: if you don't see the branches they don't matter.
Simplicity FTW. The simple loop version is very easy to understand. It's probably really fast, as it's just a loop over seven items. And more importantly it's more correct. It doesn't use floating point arithmetic, so you don't have to worry about precision issues.
The logarithmic approach is harder to reason about, prone to bugs (as proven by this post). I'm baffled at the fact that tons of people considered it a more elegant solution! It's completely the opposite!
The logarithmic approach is harder to reason about, prone to bugs (as proven by this post). I'm baffled at the fact that tons of people considered it a more elegant solution! It's completely the opposite!
the original version had branches too, in fact a majority of the lines had them! ? is just shorthand for if.
This isn't true, this form of conditionals can be compiled into cmov type of instructions, which is faster than regular jump if condition.
Both ?: and if-else have cases where they can be compiled into cmov type instructions and where they cannot. Given int max(int a, int b) { if (a > b) return a; else return b; }, a decent compiler for X86 will avoid conditional branches even though ?: wasn't used. Given int f(int x) { return x ? g() : h(); }, avoiding conditional branches is more costly than just using them, even though ?: was used.
> This isn't true, this form of conditionals can be compiled into cmov type of instructions, which is faster than regular jump if condition.
IIRC cmov is actually quite slow. It's just faster than an unpredictable branch. Most branches have predictability so you generally don't want a cmov.
Speaking of which, a couple questions regarding this for anyone who might know:
1. Can you disable cmov on x64 on any compiler? How?
2. Why is cmov so slow? Does it kill register renaming or something like that?
IIRC cmov is actually quite slow. It's just faster than an unpredictable branch. Most branches have predictability so you generally don't want a cmov.
Speaking of which, a couple questions regarding this for anyone who might know:
1. Can you disable cmov on x64 on any compiler? How?
2. Why is cmov so slow? Does it kill register renaming or something like that?
cmov itself isn't slow, it has a latency of 2 cycles on Intel; and only 1 cycle on AMD (same speed as an add).
However, cmov has to wait until all three inputs (condition flag, old value of target register, value of source register) are available, even though one of those inputs ends up going unused.
A correctly predicted branch allows the subsequent computation (using of the result of the ?: operator) to start speculatively after waiting only for the relevant input value, without having to wait for the condition or the value on the unused branch. This could sometimes save hundreds of cycles if an unused input is slow due to a cache miss.
A correctly predicted branch allows the subsequent computation (using of the result of the ?: operator) to start speculatively after waiting only for the relevant input value, without having to wait for the condition or the value on the unused branch. This could sometimes save hundreds of cycles if an unused input is slow due to a cache miss.
I wonder if there's anyone on earth who needs nicely formatted human readable file sizes that's worried about the difference between one or two cpu cycle branching instructions?
There might be a few guys at FAANG who have a planet-scale use case for human readable file sizes. But surely "performance optimising" this is _purely_ code golf geekiness?
(Which is a perfectly valid reason to do it, but I'm gonna choose the most obvious to the next progerammer reading it version over one that 50% or 500% or 5000% fast in almost any use case I can think I'm like to need this... I mean, it's only looking for 6 prefixes "KMGTPE" a six line case statement would work for most people?)
There might be a few guys at FAANG who have a planet-scale use case for human readable file sizes. But surely "performance optimising" this is _purely_ code golf geekiness?
(Which is a perfectly valid reason to do it, but I'm gonna choose the most obvious to the next progerammer reading it version over one that 50% or 500% or 5000% fast in almost any use case I can think I'm like to need this... I mean, it's only looking for 6 prefixes "KMGTPE" a six line case statement would work for most people?)
Actually, I just realised. This is (probably a small part of) why "calculate all sizes" in Mac finder windows is so slow. I already mentioned Apple in FAANG, but I guess someone at Microsoft and people who work on Linux file brokers care too. And whoever maintains the -h flag codepaths in all the Unix-like utils that support it?
Confused what this has to do with calculating file sizes. Time spent computing file sizes is dwarfed by I/O, right?
Ahh, thank you! Makes sense.
CMOV is slow because x86 processors will not speculate past a CMOV instruction. They do speculate past conditional jumps, so those are more performant.
This same property makes CMOV useful in Spectre mitigation, see https://llvm.org/docs/SpeculativeLoadHardening.html
Keeping CMOV slow is now an important security feature.
This same property makes CMOV useful in Spectre mitigation, see https://llvm.org/docs/SpeculativeLoadHardening.html
Keeping CMOV slow is now an important security feature.
They don't speculate past a CMOV at all? Like even if the next instruction has nothing to do with the CMOV's output?
I think out of order processing is considered different than speculative execution, but I could be remembering my architecture class wrong
Out-of-order just means it can rearrange the decoded uops in a way to keep the execution units at full capacity. So, if an instruction needs the ALU, but it’s busy, and the next one needs the AGU (address generation unit) and doesn’t depend on the results of the ALU one, it can “dispatch” the AGU one while the ALU one waits for the pipeline to move.
Speculative execution refers more towards the decoder/uop generation side of the processor (the “in-order” side). A normal “in-order” processor, upon encountering a conditional jump, would wait until the pipeline is finished to check if it should jump or not. It does it by inserting “bubbles” into the pipeline - essentially doing nothing but waiting.
Speculative execution (or branch prediction) would say, “I think the branch will be taken based on X, Y, Z,” and then keep the pipeline full in the process. If the prediction was right, congratulations! You just saved dozens of clock cycles that otherwise would’ve been wasted. If it was wrong, no worries. The pipeline is then flushed; all the speculated instructions’ results are tossed (before they’re “written back”). Then the processor resumes operation on the correct branch.
Speculative execution doesn’t necessitate an out-of-order architecture, and visa-versa. Just a pipelined one. It’s perfectly possible to have an out-of-order architecture that doesn’t speculate, or a speculative one that is completely “in-order”, but they work hand-in-hand, and it makes sense to have both if you have one.
Speculative execution refers more towards the decoder/uop generation side of the processor (the “in-order” side). A normal “in-order” processor, upon encountering a conditional jump, would wait until the pipeline is finished to check if it should jump or not. It does it by inserting “bubbles” into the pipeline - essentially doing nothing but waiting.
Speculative execution (or branch prediction) would say, “I think the branch will be taken based on X, Y, Z,” and then keep the pipeline full in the process. If the prediction was right, congratulations! You just saved dozens of clock cycles that otherwise would’ve been wasted. If it was wrong, no worries. The pipeline is then flushed; all the speculated instructions’ results are tossed (before they’re “written back”). Then the processor resumes operation on the correct branch.
Speculative execution doesn’t necessitate an out-of-order architecture, and visa-versa. Just a pipelined one. It’s perfectly possible to have an out-of-order architecture that doesn’t speculate, or a speculative one that is completely “in-order”, but they work hand-in-hand, and it makes sense to have both if you have one.
Is it safe to say speculation is about what to do with instructions following conditionals, and OoO is about what to do with instructions following non-conditionals?
Roughly, yes
This email thread from Linus might be interesting: https://yarchive.net/comp/linux/cmov.html
My understanding of out-of-order (and pipelined) CPUs is limited, but it’s interesting that CMOV isn’t interpreted as a “Jcc over MOV” by the decoder. That would allow using the branch predictor. Would it be too complex or does the microarchitecture not even allow it?
I think that thread is where I first learned this actually. Didn't remember it until you linked it now, thanks for posting it!
If the if/else is simple the compiler should be able to optimize that anyway.
Exactly. As the article itself mentions:
> Granted it’s not very readable and log / pow probably makes it less efficient
So, the "improved" solution is both less readable and probably less efficient... where is the improvement then?
> Granted it’s not very readable and log / pow probably makes it less efficient
So, the "improved" solution is both less readable and probably less efficient... where is the improvement then?
If it were me in my programming language, I would just use Humanizr and be freaking done with it.
The real question is why is it a bug to report 1 mB instead of 999.9 kB for human readable output? It seems like a nice excursion to FP related pitfalls, but i don't think this is a problem to get entangled in that.
Because it doesn't print 999.9 kB or 1 mB.
It prints 1000.0 kB.
It prints 1000.0 kB.
I still wouldn't consider it a bug since we are throwing lots of lsbs anyways. It matters even less when we are talking about Peta/Exa bytes.
I guarantee a design team would take one look at 1000.0kB and kick it back as a bug
As part of the Stack Overflow April Fools' prank, we did some data analysis on copy behavior on the site [0]. The most copied answer during the collection period (~1 month) was "How to iterate over rows in a DataFrame in Pandas" [1], receiving 11k copies!
[0] https://stackoverflow.blog/2021/04/19/how-often-do-people-ac...
[1] https://stackoverflow.com/a/16476974/16476924
[0] https://stackoverflow.blog/2021/04/19/how-often-do-people-ac...
[1] https://stackoverflow.com/a/16476974/16476924
That’s sad, as when you find yourself iterating over rows in pandas you’re almost invariably doing some wrong or very very sub optimally.
To me it's an means to an end. I don't care if my solution takes 100ms instead of 1ms, it's the superior choice for me if it takes me 1 minute to do it instead of 10 minutes to learn something new.
True, but sometimes these 10 minutes help you to discover something new that will improve your code.
I had a few of these cases in my life:
- discovering optimized patterns in Perl, which led to code I could not understand the next day
- discovering decorators in Python, which led to better code
- discovering comprehensions in Python (a magical thing) that led to better code, except when I wanted to be too clever and ended up with Perl-like code
I had a few of these cases in my life:
- discovering optimized patterns in Perl, which led to code I could not understand the next day
- discovering decorators in Python, which led to better code
- discovering comprehensions in Python (a magical thing) that led to better code, except when I wanted to be too clever and ended up with Perl-like code
The flaw of human nature on display. And I don't mean that personal, not to you anyway, but to the human species.
Why? It seems very rational. Especially if you're just going to run it once to get a value and not as a part of some system.
Exactly, that's not a flaw, that's rational behaviour. Why design an intricate solution for a one-off. Using 15 times the amount of time it would have taken you manually to automate a pretty standard task is just stupid, though we all do it.
Do the first thing that works, don't overthink it.
Do the first thing that works, don't overthink it.
Why learn anything at all then? Why bother learning OOP paradigms if procedural just works? Why bother ...? Do you see the flaw in your argument?
I think the flaw is you misinterpreting the argument.
In my opinion, the bottom line with obvious caveats is this - Human-time is more valuable than CPU-time.
If you are shipping at scale then the calculus is different - Don't waste end-users' human-time and their cpu-time and/or server's cpu-time.
If you're writing code with a team the calculus is different - Use/Learn techniques and tools to reduce the teams' human-time wastage plus all the above.
If you're writing code just for yourself the calculus is different - Save your own human-time.
In my opinion, the bottom line with obvious caveats is this - Human-time is more valuable than CPU-time.
If you are shipping at scale then the calculus is different - Don't waste end-users' human-time and their cpu-time and/or server's cpu-time.
If you're writing code with a team the calculus is different - Use/Learn techniques and tools to reduce the teams' human-time wastage plus all the above.
If you're writing code just for yourself the calculus is different - Save your own human-time.
One doesn’t learn rock climbing to step over a brick, man.
Because when it's not a one off?
If that was a fair comment then we’d be writing all our code in assembly still.
I iterate over rows in pandas fairly often for plotting purposes. Anytime I want to draw something more complicated than a single point for each row, I find it's simple and straight-forward to just iterrows() and call the appropriate matplotlib functions for each. It does mean some plots that are conceptually pretty simple end up taking ~5 seconds to draw, but I don't mind. Is there really a better alternative that isn't super complicated? Keep in mind that I frequently change my mind about what I'm plotting, so simple code is really good (it's usually easier to modify) even if it's a little slower.
>That’s sad, as when you find yourself iterating over rows in pandas you’re almost invariably doing some wrong or very very sub optimally.
Humans writing code is suboptimal. I can't wait for the day when robots/AI do it for us. I just hope it leads to a utopia and not a dystopia.
Humans writing code is suboptimal. I can't wait for the day when robots/AI do it for us. I just hope it leads to a utopia and not a dystopia.
I'm glad that DataFrames don't iterate by default. It's good design to make suboptimal features hard to access.
I got bitten by that prank when copying code from a question, to see what it did (it was something obviously harmless). I was rather annoyed for about two seconds before I realized what date it was. :)
> return String.format("%.1f %sB", bytes / Math.pow(unit, exp), pre);
As a human, the first thing that I hate about this interpretation of "human readable" format is inconsistency in the number of significant digits. One digit after decimal separator is simply wrong, as when you jump from 999.9 MB to 1.0 GB you go from 4 significant digits to 2, instead it should be 1.000 GB, 10.00 GB and so on. This annoys me enormously when I upload things to Google Drive from Android phone and look at the number of data transferred as as soon it becomes bigger than 1 GB digits stop changing and I become anxious that it stopped the transfer and my Windows Phone nostalgia jumps over the roof (as WP was never infected with this problem by virtue of not using Java, and OneDrive on WP explicitly showed current connection speed, and frozen connection never caused any strange problems with uploaded files like it does on Google Drive on Android).
As a human not from US, the second thing I hate here is lack of locale parameter to pass to formatter as decimal separator is different in different cultures, and in the world of cloud computing the locale of the machine where the code is run is often different from the one where the message is displayed.
As a human from a culture using non latin alphabet, the third thing I hate here should be obvious for a reader.
As a human, the first thing that I hate about this interpretation of "human readable" format is inconsistency in the number of significant digits. One digit after decimal separator is simply wrong, as when you jump from 999.9 MB to 1.0 GB you go from 4 significant digits to 2, instead it should be 1.000 GB, 10.00 GB and so on. This annoys me enormously when I upload things to Google Drive from Android phone and look at the number of data transferred as as soon it becomes bigger than 1 GB digits stop changing and I become anxious that it stopped the transfer and my Windows Phone nostalgia jumps over the roof (as WP was never infected with this problem by virtue of not using Java, and OneDrive on WP explicitly showed current connection speed, and frozen connection never caused any strange problems with uploaded files like it does on Google Drive on Android).
As a human not from US, the second thing I hate here is lack of locale parameter to pass to formatter as decimal separator is different in different cultures, and in the world of cloud computing the locale of the machine where the code is run is often different from the one where the message is displayed.
As a human from a culture using non latin alphabet, the third thing I hate here should be obvious for a reader.
I don't think it makes sense to talk about significant digits here. And while you are correct that you should not go from 999.9MB to 1.0 GB you are incorrect about your reasoning and your correction is also incorrect. Significant digits signify reliability of the numbers. So if your measurement is accurate to the +/- 50kB as indicated by 999.9MB you should then move to 1.0000 GB (5 significant digits). So it should be 10.00GB and 1.00GB not 1.000GB, because the reliability should not change between your measurements.
> instead it should be 1.000 GB, 10.00 GB and so on
I had a hard time mentally parsing that sequence even when I knew what your point was so imagine regular users seeing that.
I had a hard time mentally parsing that sequence even when I knew what your point was so imagine regular users seeing that.
As a bonus, the thing I don't care any more here is that there is no option to output binary SI prefixes.
> Key Takeaways:
> [...]
> Floating-point arithmetic is hard.
I have successfully avoided FP code for most of my career. At this point, I consider the domain sophisticated enough to be an independent skill on someone's resume.
> [...]
> Floating-point arithmetic is hard.
I have successfully avoided FP code for most of my career. At this point, I consider the domain sophisticated enough to be an independent skill on someone's resume.
There are libraries that offer more appropriate ways of dealing with it, but last time I ran into a FP-related bug (something to do with parsing xlsx into MySQL) I fixed it quickly by converting everything to strings and doing some unholy procedure on them. It worked but it wasn’t my proudest moment as a programmer.
I wish to learn a better way. FP is sure to byte again and again.
Well, manually floating the point in a string is sure to bite again and again too, but way more frequently than in binary.
There is actually no better way, if you try to calculate over the reals (with computers or whatever you want), you are prone to be bitten. Once in a while there's an article about intervalar algebra on HN, those are a great opportunity to just nod positively and remember all of the flaws of intervalar algebra I got to learn on my school's physics labs. (And yeah, those flaws do fit some problems better than FP, but not all.)
There is actually no better way, if you try to calculate over the reals (with computers or whatever you want), you are prone to be bitten. Once in a while there's an article about intervalar algebra on HN, those are a great opportunity to just nod positively and remember all of the flaws of intervalar algebra I got to learn on my school's physics labs. (And yeah, those flaws do fit some problems better than FP, but not all.)
Pity the rational numbers (fractions) did not catch on. Of course it has flaws too but bit easier to grasp. And it handles important cases like 1/3 or 1/10 exactly.
As long as you're using it to represent what could be physical measurements of real-valued quantities, it's nearly impossible to go wrong. Problems happen when you want stupendous precision or human readability.
Numerically unstable algorithms are a problem too but again, intuitively so if you think of the numbers as physical measurements.
Numerically unstable algorithms are a problem too but again, intuitively so if you think of the numbers as physical measurements.
I am regularly reminded of William Kahan's (the godfather of IEEE-754 floating point) admonition: A floating-point calculation should usually carry twice as many bits in intermediate results as the input and output deserve. He makes this observation on the basis of having seen many real world numerical bugs which are corrupt in half of the carried digits.
These bugs are so subtle and so pervasive that its almost always cheaper to throw more hardware at the problem than it is to hire a numerical analyst. Chances are that you aren't clever enough to unit test your way out of them, either.
These bugs are so subtle and so pervasive that its almost always cheaper to throw more hardware at the problem than it is to hire a numerical analyst. Chances are that you aren't clever enough to unit test your way out of them, either.
Yep, floating point numbers are intended for scientific computation on measured values; however many gotchas they hsve when used as intended, there are even MORE if you start using them for numbers that are NOT that. money or any kind of "count" rather than measurement (like, say, a number of bytes).
The trouble is that people end up using them for any non-integer ("real") numbers. It turns out that in modern times scientific calculations with measured values are not necessarily the bulk of calculations in actually written software.
In the 21st century, i don't think there's any good reason for literals like `21.2` to represent IEEE floats instead of a non-integer data representation that works more how people expect for 'exact' numbers (ie, based on decimal instead of binary arithmetic; supporting more significant digits than an IEEE float; so-called "BigDecimal"), at the cost of some performance that you can usually afford.
And yet, in every language I know, even newer ones, a decimal literal represents a float! It's just asking for trouble. IEEE float should be the 'special case' requiring special syntax or instantiation, a literal like `98.3` should get you a BigDecimal!
IEEE floats are a really clever algorithm for a time when memory was much more constrained and scientific computing was a larger portion of the universe of software. But now they ought to be a specialty tool, not the go-to for representing non-integer numbers.
The trouble is that people end up using them for any non-integer ("real") numbers. It turns out that in modern times scientific calculations with measured values are not necessarily the bulk of calculations in actually written software.
In the 21st century, i don't think there's any good reason for literals like `21.2` to represent IEEE floats instead of a non-integer data representation that works more how people expect for 'exact' numbers (ie, based on decimal instead of binary arithmetic; supporting more significant digits than an IEEE float; so-called "BigDecimal"), at the cost of some performance that you can usually afford.
And yet, in every language I know, even newer ones, a decimal literal represents a float! It's just asking for trouble. IEEE float should be the 'special case' requiring special syntax or instantiation, a literal like `98.3` should get you a BigDecimal!
IEEE floats are a really clever algorithm for a time when memory was much more constrained and scientific computing was a larger portion of the universe of software. But now they ought to be a specialty tool, not the go-to for representing non-integer numbers.
I think you are significantly underestimate the prevalence of floating point calculations, there is a reason why Intel and AMD created all the special simd instructions. Multimedia is a big user for example. You also seriously underestimate the performance cost of using decimal types, we are talking orders of magnitude.
Fair! Good point about multimedia/animation/etc.
There are still a lot of people doing a lot of work in which they hardly ever want a floating point number but end up using it because it's the "obvious" one that happens when you just write `4.2`, and the BigDecimal is cumbersome to use.
There are still a lot of people doing a lot of work in which they hardly ever want a floating point number but end up using it because it's the "obvious" one that happens when you just write `4.2`, and the BigDecimal is cumbersome to use.
I like that idea too. I wonder why Python doesn't use bigdecimals by default. Maybe because it seems to require you to choose a precision?
Notably, this is only true of 64-bit floats. Sticking to 32-bit floats saves memory and sometimes are faster to compute with, but you can absolutely run into precision problems with them. When tracking time, you'll only have millisecond precision for under 5 hours. When representing spacial coordinates, positions on the Earth will only be precise to a handful of meters.
I do a lot of floating point math at work and constantly run into problems either from someone else's misunderstanding, my own misunderstanding, or we just moved to a new microarchitecture and CPU dispatch hits a little different manifesting itself as rounding error to write off (public safety industry).
If you expect bit-for-bit reproducible results, then yea, you'd have to know about the nitty-gritty details. The values should usually still correspond to the same thing in common real world precision though.
> it's nearly impossible to go wrong
It's a matter of time if one doesn't know to look for numerically stable algorithms. Or if one thinks performance merits dropping stability.
https://github.com/RhysU/ar/issues/3 was an old saga in that vein.
It's a matter of time if one doesn't know to look for numerically stable algorithms. Or if one thinks performance merits dropping stability.
https://github.com/RhysU/ar/issues/3 was an old saga in that vein.
Unfortunately, that doesn't work when you have to do:
1 - quantity2 / (quantity1 - quantity2)
... or some such thing. If quantity1 and 2 are similar, ouch!
1 - quantity2 / (quantity1 - quantity2)
... or some such thing. If quantity1 and 2 are similar, ouch!
Not sure if there's a mistake in that expression, since if they're similar, you're already going to get some ridiculously large magnitude (unphysical) result. Maybe you mean calculating the error between two values or convergence testing? In that case, it hardly matters if whether you do
quantity2/quantity1 - 1
or
(quantity2 - quantity1) / quantity1
with double precision and physically reasonable values.
quantity2/quantity1 - 1
or
(quantity2 - quantity1) / quantity1
with double precision and physically reasonable values.
So you have problems if you want a precise answer, you want to display your answer, or if you want to use any of a large number of useful algorithms? That sounds like it’s quite easy to go wrong.
You can't want a precise answer from physical measurements unless you don't know how to measure things. Display should be done with libraries, and numerical instability makes algorithms basically useless, so you pretty much have to be inventing it yourself.
I consider the domain sophisticated enough to be an independent skill
It's been a whole field with its own patron saint for a quite a while, take a look at
https://en.wikipedia.org/wiki/William_Kahan
It's been a whole field with its own patron saint for a quite a while, take a look at
https://en.wikipedia.org/wiki/William_Kahan
Just this week I watched someone discover that computing summary statistics in 32-bit on a large dataset is a bad idea. The computer science curricula needs to incorporate more computational science. It's a shame to charge someone tens of thousands of USD and to not warn them that floating point has some obvious footcanons.
> Just this week I watched someone discover that computing summary statistics in 32-bit on a large dataset is a bad idea. The computer science curricula needs to incorporate more computational science.
Sadly, I suspect too many "computer science" courses have turned into "vocational coding" courses, and now those people are computing summary statistics on large datasets in Javascript...
Sadly, I suspect too many "computer science" courses have turned into "vocational coding" courses, and now those people are computing summary statistics on large datasets in Javascript...
Could you shed some light on what they did wrong, and what would be a better way to do it?
not OP, but the hint is in “computing summary statistics in 32-bit on a large dataset”.
A large dataset means lots of values, maybe we can assume the number of values is way bigger than any individual value. Perhaps think of McDonalds purchases nation-wide: billions of values but each value is probably less than $10.
The simplest summary statistic would be a grand total (sum). If you have a good mental model of floats, you immediately see the problem!
The mental model of floats which I use is 1) floats are not numbers, they are buckets, and 2) as you get further away from zero, the buckets get bigger.
So let’s say you are calculating the sum, and it is already at 1 billion, and the next purchase is $3.57. You take 1 billion, you add 3.57 to it, and you get... 1 billion. And this happens for all of the rest of the purchases as well.
Remember: 1 billion is not a number, it is a bucket, and it turns out that when you are that far away from zero, the size of the bucket is 64. So 3.57 is simply not big enough to reach the next bucket.
A large dataset means lots of values, maybe we can assume the number of values is way bigger than any individual value. Perhaps think of McDonalds purchases nation-wide: billions of values but each value is probably less than $10.
The simplest summary statistic would be a grand total (sum). If you have a good mental model of floats, you immediately see the problem!
The mental model of floats which I use is 1) floats are not numbers, they are buckets, and 2) as you get further away from zero, the buckets get bigger.
So let’s say you are calculating the sum, and it is already at 1 billion, and the next purchase is $3.57. You take 1 billion, you add 3.57 to it, and you get... 1 billion. And this happens for all of the rest of the purchases as well.
Remember: 1 billion is not a number, it is a bucket, and it turns out that when you are that far away from zero, the size of the bucket is 64. So 3.57 is simply not big enough to reach the next bucket.
Well explained! All of the later contributions to the sum are effectively ignored or their contributions severely damaged in 32-bit because the "buckets" are big.
It was precisely this problem. The individual had done all data preparation/normalization in 32-bit because the model training used 32-bit on the GPU. It's a very reasonable mistake if one hasn't been exposed to floating point woes. I was pleased to see that the individual ultimately caught it when observing that 2 libraries disagreed about the mean.
Computing a 64-bit mean was enough. Compensated (i.e. Kahan) summation would have worked too.
It was precisely this problem. The individual had done all data preparation/normalization in 32-bit because the model training used 32-bit on the GPU. It's a very reasonable mistake if one hasn't been exposed to floating point woes. I was pleased to see that the individual ultimately caught it when observing that 2 libraries disagreed about the mean.
Computing a 64-bit mean was enough. Compensated (i.e. Kahan) summation would have worked too.
Thanks for the explanation!
> At the very least, the loop based code could be cleaned up significantly.
Seems like the loop based code wasn't so bad after all...
Seems like the loop based code wasn't so bad after all...
This! If I had to choose between the two snippets I would have taken the loop based one without a second though, because of its simplicity.
The second snippet is what usually happens when people try to write "clever" code.
The loop by itself isn't entirely clear on what it's doing. Stuff like the direction of the > comparison and what to do vs. >= and the byteCount / magnitudes[i] at the end really do require you to pause & do mental analysis to check correctness. I think the real solution here is to define an integer log (ilog()?) function based on division and use that in the same manner as the log(). That way you only do do the analysis the first time you write that function, and after that you just call the function knowing that it's correct.
I was reading this and thought it sounded familiar. A few months ago I needed a human readable bytes format, ended up on that stack overflow article and, plot twist, copied the while loop one.
In his defences, he did admit at the start of the blog post that he was code golfing.
Loop code has the same bug.
This is Java, not JavaScript. The exponents table was likely of integer type. Then it works.
How does that avoid the misrounding bug for 999,999B = 1000KB (wrong), 1MB correct?
D'oh, you're right.
Premature optimization strikes again.
There might be an opportunity somewhere around this area to combine the versioning, continuous improvement, and dependency management of package repositories with the Q&A format of StackOverflow.
Something like "cherry pick this answer, with attribution, and notifications when flaws and/or improvements are found".
Maybe that's a terrible idea (there's definitely risk involved, and the potential to spread and create bad software), but equally I don't know why it would be significantly worse than unattributed code snippets and trends towards single-function libraries.
Something like "cherry pick this answer, with attribution, and notifications when flaws and/or improvements are found".
Maybe that's a terrible idea (there's definitely risk involved, and the potential to spread and create bad software), but equally I don't know why it would be significantly worse than unattributed code snippets and trends towards single-function libraries.
NodeJS did something a lot like this by having packages that are just short snippets, but half the ecosystem flipped out when someone messed up `leftpad`.
Well that and because having 20,000 packages in your project is a PITA in various ways.
Mostly but not entirely because NPM handled things poorly in various ways.
Mostly but not entirely because NPM handled things poorly in various ways.
Not sure if it's quite what you had in mind, but SO is starting to address the issue of updating old answers with the Outdated Answers Project: https://meta.stackoverflow.com/questions/405302/introducing-...
Very relevant, thank you!
[deleted]
Sadly updates don't just remove bugs, but sometimes also add them. Silently adding a bug to previously working code is a lot more bad than silently fixing a bug you didn't know you had is good, so I wouldn't want to have a load of self-updating code snippets in my codebase.
> Sebastian then reached out to me to straighten it out, which I did: I had not yet started at Oracle when that commit was merged, and I did not contribute that patch. Jokes on Oracle. Shortly after, an issue was filed and the code was removed.
Good thing it wasn't a range check function. I hear those are expensive.
Good thing it wasn't a range check function. I hear those are expensive.
> I wrote almost a decade ago was found to be the most copied snippet on Stack Overflow. Ironically it happens to be buggy.
I don’t find it ironic, I find it quite normal that even small snippets of code contains bugs (given the daily review requests I receive).
I think when copying code literally from StackOverflow what’s more important is understanding what the code does, and why , rather than copying it ad-verbatim by copy & pasting it into your production code.
I also often find on StackExchange et al that quite often the most upvoted is the one that ‘fixes it’ for ‘most people’ yet the correct answer is down at number 3 or 4. Again, understanding the answer and why it applies, helps give you the context to understand if this is actually the solution to your problem or just treats the symptom.
I don’t find it ironic, I find it quite normal that even small snippets of code contains bugs (given the daily review requests I receive).
I think when copying code literally from StackOverflow what’s more important is understanding what the code does, and why , rather than copying it ad-verbatim by copy & pasting it into your production code.
I also often find on StackExchange et al that quite often the most upvoted is the one that ‘fixes it’ for ‘most people’ yet the correct answer is down at number 3 or 4. Again, understanding the answer and why it applies, helps give you the context to understand if this is actually the solution to your problem or just treats the symptom.
What I realized years ago is that the upvote on Stack Overflow don't mean "I tried this and it works for me" or "I'm an expert and this is the answer". No, the upvotes on Stack Overflow are along the line of the upvotes/likes one would find on Reddit or HN. More like "you sound confident" or "I was looking for this but I haven't tried it yet"
> No, the upvotes on Stack Overflow are along the line of the upvotes/likes one would find on Reddit or HN. More like "you sound confident"
I think you're right that online scoring systems tend to incentivise false confidence. This happens with blog posts too, where a student of some topic writes a confident and subtly incorrect blog post, and it then ends up on the HN front-page. Only someone with a relatively deep knowledge of the topic can then call out the errors. Ideally it should always be made clear upfront that the author is new to the material.
Somewhat related: Stack Overflow's unfortunate norm of calling out mistakes in answers in a way that goes beyond confidence and strays into condescension and borderline hostility. For a lot of people it seems it's not enough to be seen to be right, they also feel the need to paint someone else as clueless, while just about passing as acceptably polite by keeping the aggression passive. If challenged, they'll brush it off as 'directness'.
I think you're right that online scoring systems tend to incentivise false confidence. This happens with blog posts too, where a student of some topic writes a confident and subtly incorrect blog post, and it then ends up on the HN front-page. Only someone with a relatively deep knowledge of the topic can then call out the errors. Ideally it should always be made clear upfront that the author is new to the material.
Somewhat related: Stack Overflow's unfortunate norm of calling out mistakes in answers in a way that goes beyond confidence and strays into condescension and borderline hostility. For a lot of people it seems it's not enough to be seen to be right, they also feel the need to paint someone else as clueless, while just about passing as acceptably polite by keeping the aggression passive. If challenged, they'll brush it off as 'directness'.
Also to create a democracy.
> Our sites are all intended to be a sort of representative democracy. Moderator elections are an important part of that plan, but voting on questions and answers is the primary mechanism through which the community governs the site on a day to day basis.
https://stackoverflow.com/help/why-vote
> Our sites are all intended to be a sort of representative democracy. Moderator elections are an important part of that plan, but voting on questions and answers is the primary mechanism through which the community governs the site on a day to day basis.
https://stackoverflow.com/help/why-vote
And it can fall to all the errors and issues of democracy too - especially the “pseudo-expert” one. At least you can leave a comment on the answer if there’s an issue.
experts can edit the stackoverflow answers (assuming their stackoverflow rating is high enough)
The number of times I've seen the only correct answer being a terse explanation with a short code snippet and having zero upvotes astounds me.
They may not have been the attention seekers like other posters. But they provided exactly what was asked for. And when I come across their post years later I upvote.
They may not have been the attention seekers like other posters. But they provided exactly what was asked for. And when I come across their post years later I upvote.
> More like "you sound confident"
Meh, I'm usually there looking for how to do something, and if a response helps me do whatever I was looking to acomplish, or at least on the right track, it was helpful and worth an upvote. I've never upvoted just because someone sounded confident.... at least not on SO.
Meh, I'm usually there looking for how to do something, and if a response helps me do whatever I was looking to acomplish, or at least on the right track, it was helpful and worth an upvote. I've never upvoted just because someone sounded confident.... at least not on SO.
There's also the possibility that the answer was correct when written. Especially with web stuff a year old answer could be completely wrong now.
It's a user experience issue and it's hard to solve. You can't possibly expect people to come back to one of their SO tabs AFTER they get code to work.
Why not? I dont upvote an answer unless it works...
I think it was sarcasm... just missing the /s
One of the best tips I have gotten from the internet is to never copy and paste code you have not written yourself. Even rewriting it verbatim makes you think about what it is you are actually copying.
It's a pretty neat rule to have in mind.
It's a pretty neat rule to have in mind.
Ladislav Vagner, a legendary programming tutor at FIT CTU, is a known proponent of being extremely cautious when copying code, even your own. He gives programming proseminars where students guide him as he codes the solution to some problem, e.g. mathjax-like typesetting in C++. It is a common theme in the proseminars that a bug is introduced by copying code. Probably on purpose, like many of the other bugs that students are supposed to point out.
I think that’s true if you’re trying to learn a new tool or technology. You probably won’t learn as much following the Rails or Django tutorials if you’re just pasting all the code. But if you’re just looking for some esoteric workaround for some very specific tool and use case, I think it’s fine to paste. And the latter makes up the overwhelming majority of my Stack Overflow visits.
It's also good legal advice. It's now legally possible for you to copy and paste code directly from stack overflow because they made an effort to assert a compatible license over works published on their site. However, the same can't be said for most other code snippets flying around out there.
Good point in case: license of the code in this exact article is very likely incompatible with your production code.
When you get into this habit it also makes it easier to translate solutions from other languages too
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Yes, and:
I didn't really grok Test Driven Development until I worked thru the book, line-by-line, experiencing the workflow.
Knowledge vs experience.
I didn't really grok Test Driven Development until I worked thru the book, line-by-line, experiencing the workflow.
Knowledge vs experience.
Agreed. Otherwise it's not uncommon for me to not know what 80% of the code is even capable of...
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> I also often find on StackExchange et al that quite often the most upvoted is the one that ‘fixes it’ for ‘most people’
And also first, or at least early, and subject to a reinforcing cycle of 'sufficiently good' or 'fixed it enough' that it achieves stratospherically more votes than an 'even more good' or 'fixes it properly' answer that came in too late for the same traction.
And also first, or at least early, and subject to a reinforcing cycle of 'sufficiently good' or 'fixed it enough' that it achieves stratospherically more votes than an 'even more good' or 'fixes it properly' answer that came in too late for the same traction.
> also first, or at least early, and subject to a reinforcing cycle of 'sufficiently good' or 'fixed it enough'
So exactly the solution most project managers are after? /s
So exactly the solution most project managers are after? /s
Ha, well even if there's an argument for that, it quite often leads to (and is even more reinforced by in terms of votes) the original asker 'accepting' the solution; then the answer that 'fixed it for them, first' is forever ranked highest, even if it rarely works for others and something else is more up-voted.
Remember the npm left-pad disaster? That code had bugs in it. See slide 44: https://www.slideshare.net/Kevlin/good-code-73714882
This works better when the problem does not 100% match the issue you are tackling. It makes you think about how you can reshape what you found into something useful.
IMHO any code that tries to perform floating-point arithmetic on integer values and then produce exact output should be considered suspect in and of itself...too many edge cases.
> The most copied StackOverflow snippet of all time
Maybe, but sounds like it's merely the Java snippet from SO found most often on github. Not sure why blog author didn't include the word "Java" in his title or the first paragraph:
> an answer I wrote almost a decade ago was found to be the most copied snippet on Stack Overflow
There is no evidence for this claim in the blog post, just that it's the "most copied Java snippet". And it's just based on occurrences in github. Maybe the most-copied snippet is an AWK or ffmpeg one-liner? Something that wouldn't find its way into a github repo. Or maybe something undetectably vanilla, like answers to "How do you write loops in language X?" Is there a way of finding out what actually is the most-copied snippet?
Maybe, but sounds like it's merely the Java snippet from SO found most often on github. Not sure why blog author didn't include the word "Java" in his title or the first paragraph:
> an answer I wrote almost a decade ago was found to be the most copied snippet on Stack Overflow
There is no evidence for this claim in the blog post, just that it's the "most copied Java snippet". And it's just based on occurrences in github. Maybe the most-copied snippet is an AWK or ffmpeg one-liner? Something that wouldn't find its way into a github repo. Or maybe something undetectably vanilla, like answers to "How do you write loops in language X?" Is there a way of finding out what actually is the most-copied snippet?
I don’t know how you’d find it, but if I had to bet it would be something to do with git.
This is a bit of a tangent, but while it may be conventional to round to the value with the smallest difference, is that convention good? In a case such as this where it's fine for the prescision to vary with magnitude, then I'd argue it makes sense to round to the value with the smallest ratio.
The thing that jumped out at me, as I've seen the same kind of thing on the job, is the assumption that, eg, log(1000)/log(10) is exactly 3. Does the standard guarantee that the rounded approximation of one transcendental number by the rounded approximation of a related transcendental number will give 3.0 and not 2.999999999?
Yeah that seems like a serious flaw to me too. On my Python:
>>> math.log(1000)/math.log(10)
2.9999999999999996
>>> int(math.log(1000)/math.log(10))
2
Floating point math is IEEE 754 in pretty much all cases, so you should see this result in most languages. `math.log(1000, 10)` gives the same result because it's implemented using natural logs internally as it is in most languages.
In this case, there's only about six boundary cases to consider so you can just manually verify it works as expected.
In this case, there's only about six boundary cases to consider so you can just manually verify it works as expected.
I don't think this works very well as a cautionary tale because honestly, I would not even care about a bug like this. It's something very few people would even figure out exists at all, it's incredibly inconsequential.
You’ve made a judgement call that correctness isn’t a priority in this circumstance, and as long as your judgement is sound, this approach will serve you well.
The weakness of your approach is that no one’s judgment is sound 100% of the time.
Alternatively, folks who always prioritize correctness may occasionally “waste their time”, but two things to consider: 1) their judgement is no longer an issue, and 2) in the long run they have spent more time training their correctness muscles and are in better shape.
The weakness of your approach is that no one’s judgment is sound 100% of the time.
Alternatively, folks who always prioritize correctness may occasionally “waste their time”, but two things to consider: 1) their judgement is no longer an issue, and 2) in the long run they have spent more time training their correctness muscles and are in better shape.
However this "bug" is still entirely within spec. The whole article hinges on "the 1,000 “significand” is out of range according to spec", but it really isn't. 999999 Bytes are indeed around 1000kB. Sure, calling it 1MB would be preferable, but saying 1000kB doesn't violate any rule, is perfectly acceptable according to SI (just like I can say 1000g or 1kg interchangeably), fulfills the task of being human readable, and in all the examples given in the task the code behaves as requested.
Sure, the code doesn't do exactly what the programmer wanted. But that doesn't necessarily make it incorrect.
Sure, the code doesn't do exactly what the programmer wanted. But that doesn't necessarily make it incorrect.
This reminds me of my favourite SO answer:
https://stackoverflow.com/a/40429822/864112
It boggles the mind that anyone could ever suggest this as a solution.
https://stackoverflow.com/a/40429822/864112
It boggles the mind that anyone could ever suggest this as a solution.
Wow. Nice comment...
> This is akin to answering "how do I bake a cake?" with "open up a bakery, walk inside, and ask for a cake"
Only it's more like answering "how much does this cake cost" by purchasing the cake and looking at the receipt.
> This is akin to answering "how do I bake a cake?" with "open up a bakery, walk inside, and ask for a cake"
Only it's more like answering "how much does this cake cost" by purchasing the cake and looking at the receipt.
You'd think that is so completely wrong that no competent programmer would ever do it...
Except the java.net.URL.equals and java.net.URL.hashcode methods do almost the same thing: they issue DNS requests (!)
"Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null."
See https://docs.oracle.com/en/java/javase/11/docs/api/java.base...
There is a bug raised[1], but it can't be fixed for backwards compatibility reasons.
I'll never forget this now, after debugging a very horrible and severe and very intermittent performance issue in some code over 20 years ago. A (slow) DNS resolver occasionally caused 1000x performance degradation on remote sites. That was horrible to work out.
[1] https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4434494
Except the java.net.URL.equals and java.net.URL.hashcode methods do almost the same thing: they issue DNS requests (!)
"Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null."
See https://docs.oracle.com/en/java/javase/11/docs/api/java.base...
There is a bug raised[1], but it can't be fixed for backwards compatibility reasons.
I'll never forget this now, after debugging a very horrible and severe and very intermittent performance issue in some code over 20 years ago. A (slow) DNS resolver occasionally caused 1000x performance degradation on remote sites. That was horrible to work out.
[1] https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4434494
I'm going to choose to believe that is a joke answer
Ew. Yikes. Wow, that's a special kind of special. The mind truly boggles. It had a score of 4 when I first checked it, but it looks like it got slashdotted by this thread/link and now it's -1 and probably still falling.
Good.
Good.
At the time I'm writing this, the answer got 3 upvotes, 13 downvotes and 1 delete vote since the link has been posted: https://stackoverflow.com/posts/40429822/timeline?filter=Wit...
TIL: that timeline feature is really neat! I don't see a way to get to it from the mobile UI though, will need to hunt around.
I'm intrigued, why?
I find multiple places where this is the most basic implementation.
https://realpython.com/python-requests/#query-string-paramet...
https://www.geeksforgeeks.org/get-post-requests-using-python...
etc
etc
The question was how to build a URL, not how to send off a request to it. The answer sends off a request and then inspects the response to see what URL was used. If you wanted to send off the request, inspecting the URL on the result is probably not useful. If you didn't want to send off the request, doing it this was is wasteful or even harmful.
Yes, but unless the answer was edited before the link to HN was posted, the user specifically said you should only do it if you _really_ intend to make a request, not just generate a url. It is conceivable you'd want to log the request or something and hence reference the url after the request call. Yeah, it is a bad answer to the question as stated, but it has a logic to it considering what might be the real motivation behind the question.
EDIT: Apparently the answer was edited by another user just recently making the clarification.
EDIT: Apparently the answer was edited by another user just recently making the clarification.
Interesting, thanks!
Your parent poster makes the mistake that is rife among Python programmers, which is to assume that in a delightfully simple[0] language like Python, it's "obvious" what a given piece of code does even without explanation. Among people who don't delight in the poor taste of Python's design and have limited exposure to its standard library, of course, it's not always obvious what a given piece of code is doing despite the belief to the contrary, so there are plenty of people who aren't going to pick up on the fact that requests.get doesn't just construct a GET request for the caller, but instead constructs such a request and then goes out and performs it, too.
Shame about the hostile reaction from others towards your question. Keep asking questions (especially things that are presented without comment), and don't be afraid that doing so will make you look stupid or that you should feel like you should be punished for it.
0. https://blog.imgur.com/wp-content/uploads/2017/06/mocking.jp...
Shame about the hostile reaction from others towards your question. Keep asking questions (especially things that are presented without comment), and don't be afraid that doing so will make you look stupid or that you should feel like you should be punished for it.
0. https://blog.imgur.com/wp-content/uploads/2017/06/mocking.jp...
> Shame about the hostile reaction from others towards your question.
I agree that your parent is a good question that should have been well received, but, as far as I can tell, it was. Where do you see a hostile reaction? In fact the only hostility I see in this thread is what you directed at Python, which, in this context, seems unmotivated; it is surely true that one can write code in any language whose full import isn't immediately apparent. At the moment, the only other response to your parent is from hvdijk, saying (https://news.ycombinator.com/item?id=27534803):
> The question was how to build a URL, not how to send off a request to it. The answer sends off a request and then inspects the response to see what URL was used. If you wanted to send off the request, inspecting the URL on the result is probably not useful. If you didn't want to send off the request, doing it this was is wasteful or even harmful.
This seems like a response that takes the question seriously and addresses it clearly, just as it should.
I agree that your parent is a good question that should have been well received, but, as far as I can tell, it was. Where do you see a hostile reaction? In fact the only hostility I see in this thread is what you directed at Python, which, in this context, seems unmotivated; it is surely true that one can write code in any language whose full import isn't immediately apparent. At the moment, the only other response to your parent is from hvdijk, saying (https://news.ycombinator.com/item?id=27534803):
> The question was how to build a URL, not how to send off a request to it. The answer sends off a request and then inspects the response to see what URL was used. If you wanted to send off the request, inspecting the URL on the result is probably not useful. If you didn't want to send off the request, doing it this was is wasteful or even harmful.
This seems like a response that takes the question seriously and addresses it clearly, just as it should.
At the time I wrote the comment it was clearly not well-received, and the oblique opening remark from the person you're quoting is not the kind of response that addresses the question as it should.
That comment is, just like the downvotes the question received, precisely the sort of thing that discourages asking honest questions rather than welcoming them. Note that by the way it is written it, too, assumes that it is both obvious and understood that Python's request.get will "send off a request"—instead of merely building a request and returning it to you. Rather than just straightforwardly answering the question (by explaining what this part of the Python' standard library is actually doing—which is the relevant missing piece here, and which no one should be expected to know) the quoted comment ("The question was how to build a URL, not how to send off a request to it") pins the misunderstanding on the questioner by tacitly implying the questioner isn't paying attention to something else entirely different.
The comment, when considered in full and in context, actually has the effect of subtly discouraging/admonishing the questioner (and likeminded people with the same question) for failing to recognize something that is, to the sophomoric Python crowd, obvious and worthy of ridicule—which is what maest's thread was all about, by the way (and almost certainly why it got moderated).
That comment is, just like the downvotes the question received, precisely the sort of thing that discourages asking honest questions rather than welcoming them. Note that by the way it is written it, too, assumes that it is both obvious and understood that Python's request.get will "send off a request"—instead of merely building a request and returning it to you. Rather than just straightforwardly answering the question (by explaining what this part of the Python' standard library is actually doing—which is the relevant missing piece here, and which no one should be expected to know) the quoted comment ("The question was how to build a URL, not how to send off a request to it") pins the misunderstanding on the questioner by tacitly implying the questioner isn't paying attention to something else entirely different.
The comment, when considered in full and in context, actually has the effect of subtly discouraging/admonishing the questioner (and likeminded people with the same question) for failing to recognize something that is, to the sophomoric Python crowd, obvious and worthy of ridicule—which is what maest's thread was all about, by the way (and almost certainly why it got moderated).
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upvoted
Say what you want about the stability of the npm ecosystem, but if this were JS, a new SemVer patch release could be cut, and it would be fixed in thousands of code bases essentially instantly.
I like the way v8 handles this problem: https://github.com/v8/v8/blob/dc712da548c7fb433caed56af9a021...
seems that most comments here missed the end of the article , where he points to the "production ready" version of the solution, that is indeed very close to the original one, including a while loop.
> ..."production ready" version of the solution, that is indeed very close to the original one, including a while loop.
What's missing still is a comprehensive set of test cases to check against.
If such cases were spec'ed to go along with the original code, fthen at least one could have seen the applicability range and perhaps other people would have added some challenging corner cases (just as mentioned in the OP).
What's missing still is a comprehensive set of test cases to check against.
If such cases were spec'ed to go along with the original code, fthen at least one could have seen the applicability range and perhaps other people would have added some challenging corner cases (just as mentioned in the OP).
It's especially ironic given that this is about a StackOverflow code snippet that many people probably also copied without reading.
Neither is production ready because they have no code comments. And if ever there was code requiring comments, this is it.
This specific example is a good example why you should keep code as simple as possible, and why even "simple" math needs special care when testing (Because floats are not simple.)
When I'm explaining logarithms, I find it helps to relate it to the number of digits. This code is a good example of the concept: you don't need log, just convert the int to a string and check its length. A string with 1-3 digits is bytes, 4-6 is kb, etc.
> almost no branches
I wonder whether the author is suggesting that (potentially) nine branches is a small number, or they overlooked ternary expressions and function calls and are just counting the if statement.
I wonder whether the author is suggesting that (potentially) nine branches is a small number, or they overlooked ternary expressions and function calls and are just counting the if statement.
There are tons of branches in those log and pow calls. Programmers are lost in branch free religion.
It seems to me that the elegant solution would involve an instruction that returns the first non-zero bit of the number - but I don’t know if such a instruction exists in assembly.
Basically lzcnt or leading zero count on x86:
https://www.felixcloutier.com/x86/lzcnt
> It should be noted that on processors that do not support LZCNT, the instruction byte encoding is executed as BSR.
This. Boggles.
This. Boggles.
https://stackoverflow.com/a/43443701 - interesting - it seems to be a side effect of changing meaning of an instruction.
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Why are you writing code? The question was for a static method in Apache Commons, not your "I'm so clever" implementation. Think the reading comprehension is flawed.
(Of course, this static method exists in Apache Commons, going back at least 20 years. But the fellow "code golfers" of the author voted someone to the first answer who similarly had the irresistible urge to try to be very clever. It's a scourge on StackOverflow.)
(Of course, this static method exists in Apache Commons, going back at least 20 years. But the fellow "code golfers" of the author voted someone to the first answer who similarly had the irresistible urge to try to be very clever. It's a scourge on StackOverflow.)
I think that the answer is what I would expect based on the question title (which doesn’t mention Apache Commons, only Java), if I was another user searching for the solution to this problem. Maybe the question should have been renamed to indicate this, but as it stands, I do think a library-agnostic solution is more helpful to people finding the question than an answer which only works for Apache Commons.
Something about this comes off as amateurish. The obsession with minimization. Just use a switch statement. Now where is the bug going to hide? The solution doesn't need to generalize, there is only a small handful of different solutions. Just break them all out. It's more maintainable and readable and requires less thinking.
I don't know why you are being downvoted. The best solution here is for the author to admit using log was a bad idea and rewrite an entirely different version.
Coincidentally I had to write this today, and perplexingly none of the answers on that popular question seem to be as efficient and readable as what I wrote:
function prettyPrintBytesSI(x: number): string {
const magnitude = Math.abs(x)
if (magnitude < 1e3) return `${x} B`
else if (magnitude < 1e6) return `${x/1e3} kB`
else if (magnitude < 1e9) return `${x/1e6} MB`
else if (magnitude < 1e12) return `${x/1e9} GB`
else if (magnitude < 1e15) return `${x/1e12} TB`
else if (magnitude < 1e18) return `${x/1e15} PB`
else return `${x} B`
}Honestly. The code is fine.
This is for presenting stuff in a user interface. Who cares if you can find some weird edge case using MAX_LONG and MAX_DOUBLE which never will occur in practice.
This is for presenting stuff in a user interface. Who cares if you can find some weird edge case using MAX_LONG and MAX_DOUBLE which never will occur in practice.
Until it does.
The original doesn't have types, but the modified version of humanReadableByteCount() uses a "long bytes" and as such will fail if the file size is (Long.MAX_VALUE+1) because it cannot even accept the correct size as its argument in the first place. Implementing these edge cases makes adds one more working case to 2^63 (2^64 if negative file sizes are valid) when the bigger problem is using the type "long" when files of that size are possible on the target system.
Readability and maintainability matters far more.
And no - the edge cannot occur as it would require a file / whatever to have that size.
And no - the edge cannot occur as it would require a file / whatever to have that size.
For example - what is the meaning of the parameter "si"?
I betcha that is going to give you more bugs than the edge cases discussed here.
I betcha that is going to give you more bugs than the edge cases discussed here.
The parameter "si" here stands for International System of Units, or SI for short [0].
0: https://en.wikipedia.org/wiki/International_System_of_Units#...
0: https://en.wikipedia.org/wiki/International_System_of_Units#...
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My top Stack Overflow answer of all time is a now rather dated two lines of JavaScript: how to tell if a variable is undefined. I posted this in 2010 and have been getting points for it steadily for a decade, now exceeding the amount I garnered from all other activities while actively using the site. I don’t do js anymore but from what I understand the answer hasn’t been accurate since 2016 or something.
The proposed solution is crazy. Logarithms are extremely expensive to compute. No way is this code more efficient than the loop it "replaced".
That there then are numeric stability issues and a pretty gross fudge factor is used to fix them worsens the situation. I would have a quiet word with any programmer I worked with that came up with this "solution".
That there then are numeric stability issues and a pretty gross fudge factor is used to fix them worsens the situation. I would have a quiet word with any programmer I worked with that came up with this "solution".
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Fun fact: The reason Safari/Chrome/Firefox had to freeze the MacOS version in the User-Agent string is because of a code-snippet from StackOverflow that assumed the version started with "10" that snuck its way all over the place, including the Unity web player and a major wordpress templete.
It disturbs me that the authors answer became the top answer. It didn’t have a loop but was less efficient than the already accepted answer, and worse, much more complicated for a human to read and understand. It seems we are always drawn to be clever, when perfection is found in simplicity.
Overkill. KISS. n counts moving the decimal left 3 places until there are <=3 digits left. Keep one place to the right.
"BKMGTPE". n==0 => 'B'; n==4 => 'T'.
810 has 3 digits. n==0, 810B.
999950 has 6 digits. n==1, you've got 999.9K
1100000 has 7 digits. n==2, 1.1M
1234567890 has 10 digits. n==3, 1.2G
"BKMGTPE". n==0 => 'B'; n==4 => 'T'.
810 has 3 digits. n==0, 810B.
999950 has 6 digits. n==1, you've got 999.9K
1100000 has 7 digits. n==2, 1.1M
1234567890 has 10 digits. n==3, 1.2G
Interesting how the same things crop up over time. I remember seeing this on HN when it was written in 2019 :)
https://news.ycombinator.com/item?id=21698619
Still, a good lesson!
https://news.ycombinator.com/item?id=21698619
Still, a good lesson!
What sticks out for me is that people don’t even rename functions when copypasting from SO.
I know everyone is on their high horse about copying code but if you were/are to copy code keeping it the same is super valuable because invertible when someone comes a long later googling it will take them to where it was copied from originally.
When I'm "inspired" by code from somewhere, I go ahead and put the URL in there in a comment
Reminds me of this article on roman numerals https://kevlinhenney.medium.com/out-of-control-97ed6efa2818
I must admit I smiled at seeing that I edited the question, back in the day. :) Can't say I remember the question, and didn't know it has that epic feature of being the most-copied. Cool!
You have to be a terrible programmer to even consider using a base 10 logarithm for this.
Their proposed improvement is also terrible, since it divides multiple times unnecessary, and checks for negativity multiple times unnecessarily.
The proper simple solution is of course a handwritten binary search with if-else blocks that starts with the most likely range, annotated with "likely" annotations, and a single division.
If this is the main task of the program for a while, and thus a large fraction of the cache can be dedicated to it, then solutions with large lookup tables are worth trying (obviously optimizing string formatting is also essential in this case).
This is why software is so often broken, there's a lot of incompetent people programming.
Their proposed improvement is also terrible, since it divides multiple times unnecessary, and checks for negativity multiple times unnecessarily.
The proper simple solution is of course a handwritten binary search with if-else blocks that starts with the most likely range, annotated with "likely" annotations, and a single division.
If this is the main task of the program for a while, and thus a large fraction of the cache can be dedicated to it, then solutions with large lookup tables are worth trying (obviously optimizing string formatting is also essential in this case).
This is why software is so often broken, there's a lot of incompetent people programming.
"You have to be a terrible programmer to even consider using a base 10 logarithm for this."
That's not a fair statement.
Good programmers are programmers who deliver value - who build robust, maintainable features in reasonable time that address user needs.
Whether or not you would quickly find the correct approach to this specific problem is a miniscule, pedantic detail in a giant ocean of programming skills and experiences.
That's not a fair statement.
Good programmers are programmers who deliver value - who build robust, maintainable features in reasonable time that address user needs.
Whether or not you would quickly find the correct approach to this specific problem is a miniscule, pedantic detail in a giant ocean of programming skills and experiences.
You are replying to a satirical comment, I think.
You may think that, but I’m partial to the ‘for-loop version’ that everybody and their dog can understand.
About the "terrible" aspect of it, to quote: "Granted it’s not very readable and log / pow probably makes it less efficient than other solutions. But there were no loops and almost no branching which I thought was pretty neat." No need to insult the author over it.
About your "proper simple solution": I don't think that's a good idea either. Based on your next paragraph, the version you suggest with the handwritten binary search and "likely" annotations is for the case where the code isn't performance critical: for where the code is performance critical, you suggest a different solution. If the code isn't performance critical, please do not turn it into an unreadable mess over what would become a negligible overall performance gain. Write it in a simple, obviously correct way, keep it boring, and you'll keep it stable; you can use the time you save on fixing bugs in your super optimised version on improving more critical parts of your program.
About your "proper simple solution": I don't think that's a good idea either. Based on your next paragraph, the version you suggest with the handwritten binary search and "likely" annotations is for the case where the code isn't performance critical: for where the code is performance critical, you suggest a different solution. If the code isn't performance critical, please do not turn it into an unreadable mess over what would become a negligible overall performance gain. Write it in a simple, obviously correct way, keep it boring, and you'll keep it stable; you can use the time you save on fixing bugs in your super optimised version on improving more critical parts of your program.
[deleted]
Wait. I always use logarithm for this kind of tasks, how exactly does it make me incompetent and terrible? This is literally what logarithm represents?
You're right, however I think they were going for a "branchless" version just to see if they could.
[deleted]
This is why it's a good idea to have a real integer type.
Isn't it impossible? Integers go arbitrarily large but computers don't.
It is possible within the limits of available memory on the computer. Rather than the usual limit of a fixed number of bits.
I've ironically found that big integer libraries sometimes optimize math routines more than string conversion. This was quite annoying for me when I optimized the factorial function in Ruby, and found that generating the string was my bottleneck. I then optimized that as well. :-)
I've ironically found that big integer libraries sometimes optimize math routines more than string conversion. This was quite annoying for me when I optimized the factorial function in Ruby, and found that generating the string was my bottleneck. I then optimized that as well. :-)
They can go large enough for anything that matters.
A quick Google says there's an estimate of 10^78 to 10^82 atoms in the universe. That number would be able to be stored in well under 300 bits.
A quick Google says there's an estimate of 10^78 to 10^82 atoms in the universe. That number would be able to be stored in well under 300 bits.
Universe is tiny compared to mathematics and software, even simply RSA keys are already 2048bit.
Lots of problems suffer from 'combinatorial explosion' [1].
I recently learned about the Archimedes's cattle problem, the solution is of order 10^206544 [2]
[1] https://en.wikipedia.org/wiki/Combinatorial_explosion
[2] https://en.wikipedia.org/wiki/Archimedes%27s_cattle_problem
Lots of problems suffer from 'combinatorial explosion' [1].
I recently learned about the Archimedes's cattle problem, the solution is of order 10^206544 [2]
[1] https://en.wikipedia.org/wiki/Combinatorial_explosion
[2] https://en.wikipedia.org/wiki/Archimedes%27s_cattle_problem
10^206544 would still be less than 8 kB. You could store it on an Atari cartridge!
Computers also go arbitrarily large. Not infinite, but arbitrarily large.
A real number type could be bounded by the amount of RAM you have.
A real number type could be bounded by the amount of RAM you have.
You can use disk storage too. And network storage.
Does Math.log really faster than simple loop with just a couple of iterations after JIT compilation?
> Granted it’s not very readable and log / pow probably makes it less efficient than other solutions
When the author started introducing all the calculations to figure out if the printed version would round up, my first thought was, why not just look at the printed version? Print it as %.1f, then chop off anything past the period and re-parse it as an integer. Now you can trivially tell if it rounded up past the threshold and you need to bump the suffix.
Wouldn't it be cool if you could call stack overflow answers directly from your code?
You can, it's called NPM
Shows how much people enjoy writing code (puzzle solving) and hate writing unit tests.
At the very least, the loop based code could be cleaned up significantly.
previous discussion: https://news.ycombinator.com/item?id=21698619
Update title: this is from 2019
is it reasonable to assume a strong correlation between "copied code" and number of upvotes? #trolling #kiddingnotkidding
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So it's not flawed (it does compute the correct result).
The author just thinks a completely unreadable (but supposedly faster) variant using logarithms is "better" than the simple loop used in the original snippet?
Write your code for junior devs in their first week at your company, not for academic journals.
The author just thinks a completely unreadable (but supposedly faster) variant using logarithms is "better" than the simple loop used in the original snippet?
Write your code for junior devs in their first week at your company, not for academic journals.
I think you might have misread the post. His logarithm code became the most used snippet and had the bug.
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His code snippet had rounding errors on the boundaries towards the next unit.
However he notes:
> FWIW, all 22 answers posted, including the ones using Apache Commons and Android libraries, had this bug (or a variation of it) at the time of writing this article.
However he notes:
> FWIW, all 22 answers posted, including the ones using Apache Commons and Android libraries, had this bug (or a variation of it) at the time of writing this article.
Sibling commenters have already pointed out that you seem to have misread the post, but tbh I found it quite confusing to follow myslf, so here's a summary:
- the first answer posted on SO was a simple loop
- the author posted a 2nd (supposedly faster but less readable) answer. The author didn't think this answer was better than the loop, but it seems the community did and it became accepted (and extremely popular). THIS is the version that was buggy.
The author later went back and fixed their own buggy version.
So yes there's an argument to be made that the very first simple loop was better, but that's orthogonal to the point of the story.
- the first answer posted on SO was a simple loop
- the author posted a 2nd (supposedly faster but less readable) answer. The author didn't think this answer was better than the loop, but it seems the community did and it became accepted (and extremely popular). THIS is the version that was buggy.
The author later went back and fixed their own buggy version.
So yes there's an argument to be made that the very first simple loop was better, but that's orthogonal to the point of the story.
Can you please read the article all the way before commenting next time?
The log approach _is_ the most copied snippet.
The log approach _is_ the most copied snippet.
> Write your code for junior devs in their first week at your company, not for academic journals.
Hard and fast rules about coding style are silly. There's a time and place for clever code, and there's a time and place for verbose and straightforward code.
I write performance-critical code. Juniors shouldn't be mucking about there, because it's performance critical. I also write non-performance-critical code with some effort. I write that stuff for the juniors.
When writing for academic journals, it looks like the stuff I write for juniors. I'll drop a hint here or there so experts can reproduce less-obvious optimizations.
Hard and fast rules about coding style are silly. There's a time and place for clever code, and there's a time and place for verbose and straightforward code.
I write performance-critical code. Juniors shouldn't be mucking about there, because it's performance critical. I also write non-performance-critical code with some effort. I write that stuff for the juniors.
When writing for academic journals, it looks like the stuff I write for juniors. I'll drop a hint here or there so experts can reproduce less-obvious optimizations.
He ends the blog post with this: "Personally I would not copy this snippet into production code."
He isn't trying to get people to use the log version.
He isn't trying to get people to use the log version.
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You should almost _always_ focus on code readability and simplicity over inventiveness and cleverness.
Very few people I have encountered have complained about code being 'too simple' or 'too readable', but the opposite happens on a near daily/weekly basis.
Write comments, use a for loop, avoid global state, keep your nesting limited to 2-3 levels, be kind to your junior devs.
Very few people I have encountered have complained about code being 'too simple' or 'too readable', but the opposite happens on a near daily/weekly basis.
Write comments, use a for loop, avoid global state, keep your nesting limited to 2-3 levels, be kind to your junior devs.
Floating point is really really hard to get right, especially if you want the numbers to be stable. Which begs the question, why the heck does JavaScript, the most used language in the world, not have an integer type? Sure, there's BigInt but that's quite clunky to use. I know it's virtually impossible to add by now, but I'd love a integer type for all my bit twiddling, byte munching needs.
I just feel if you have bit twiddling, byte munching needs JavaScript shouldn't be the language of choice. Doing that is a rather rare edge case and if you're doing it for performance reasons, working in Javascript is the much bigger performance problem.
If you're already using JavaScript for some other reasons but occasionally have bit twiddling, byte munching needs, then trying to do that in JavaScript makes perfect sense. Is it the fastest option? No. But according to https://benchmarksgame-team.pages.debian.net/benchmarksgame/... it is generally within a factor of 4-5 of C++.
For an application area where this applies, consider a web-based game. Using JavaScript keeps you from shipping another application. But occasionally you may have bit twiddling and/or byte munching needs. Which you need to do in JavaScript.
For an application area where this applies, consider a web-based game. Using JavaScript keeps you from shipping another application. But occasionally you may have bit twiddling and/or byte munching needs. Which you need to do in JavaScript.
My point wasn't to say you should never do byte manipulation in Javascript, but that for these rare edge cases the existing capabilities without a native int are fine and if you would really need the native int rather than some equivalent work around (which I assume is most likely due to performance considerations) a faster language is the better approach. A webgame might be able to use wasm for that.
That may be true but another case where floating point should be avoided is with money. Now think about all the times a web developer innocuously used a JS number to represent a price. I wouldn’t be surprised if floating point errors affected billions of dollars of transactions.
The author's lookup table is incorrect.
The question being answered clearly wanted base2 engineering prefix units, rather than the standard base10 engineering prefix units.
suffixes = [ "EB", "PB", "TB", "GB", "MB", "KB", "B" ]
magnitudes = [ 2^60, 2^50, 2^40, 2^30, 2^20, 2^10, 2^0 ] // Pseudocode, also 64 bit integers required. (Compilers might assume unsigned 32 for int)
The question being answered clearly wanted base2 engineering prefix units, rather than the standard base10 engineering prefix units.
suffixes = [ "EB", "PB", "TB", "GB", "MB", "KB", "B" ]
magnitudes = [ 2^60, 2^50, 2^40, 2^30, 2^20, 2^10, 2^0 ] // Pseudocode, also 64 bit integers required. (Compilers might assume unsigned 32 for int)
That is not the author's code. That is pseudocode for one of the example answers that he is improving on.
The author's code gives an option for the units:
int unit = si ? 1000 : 1024;
The author's code gives an option for the units:
int unit = si ? 1000 : 1024;
If you do this you should add an 'i' to the prefixes to denote that you mean the binary notation. e.g: kiB, MiB, GiB, TiB, etc
That code snippet is explicitly introduced in the article as not the author's.
I think this shows an example of a big problem with StackOverflow compared to its initial vision. I remember listening to Jeff and Joel's podcast, and hearing the vision of applying the Wikipedia model to tech Q&A. The idea was that answers would continue to improve over time.
For the most part, they don't. I'm not quite sure if it's an issue of incentives or culture. Probably some of both. I think that having a person's name attached to their answer, along with a visible score really gives a sense of ownership. As a result, other people don't feel enabled to come along and tweak the answer to improve it.
Then, once an answer is listed at the top, it is given more opportunity for upvotes, so other improved answers don't seem to bubble up. This is a larger issue with most websites that sort by ratings. Generally they sort items based on the total number of votes, including hacker news itself. Instead, to measure the quality of an item, we should look at the number of votes, divided by the number of views. It may be tough to measure the number of views of an item, but we should be able to get a rough estimate based on the position on a page, for example.
If the top comment on a HN discussion is getting 100 views in a minute and 10 upvotes, but the 10th comment down gets 20 views and 5 upvotes, the 10th comment is likely a better quality comment. It should be sorted above the top ranked comment! There would still need to be some smoothing and promotion of new comments to get them enough views to measure their quality as well.
Such a policy on StackOverflow would also help newer, but better answers sort to the top.