Begrudgingly Choosing CBOR over MessagePack(taylor.town)

    // For each representative native type...
    cbor_read_t cbor_read_float(struct cbor *ctx, float *f);

    // And there is a generic number handling:
    struct cbor_num {
        int sign; // -1, 0 or 1
        int base; // 10 or 16
        int exponent;
        const char *digits;
        size_t digits_len;
    };
    cbor_read_t cbor_read_number(struct cbor *ctx, struct cbor_num *num);

    // And then someone will define the following on top of cbor_read_number:
    cbor_read_t my_cbor_read_mpz(struct cbor *ctx, mpz_t num);