How to implement a bitset in C?

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CCAN has a bitset implementation you can use: http://ccan.ozlabs.org/info/jbitset.html

But if you do end up implementing it yourself (for instance if you don’t like the dependencies on that package), you should use an array of ints and use the native size of the computer architecture:

#define WORD_BITS (8 * sizeof(unsigned int))

unsigned int * bitarray = (int *)calloc(size / 8 + 1, sizeof(unsigned int));

static inline void setIndex(unsigned int * bitarray, size_t idx) {
    bitarray[idx / WORD_BITS] |= (1 << (idx % WORD_BITS));
}

Don’t use a specific size (e.g. with uint64 or uint32), let the computer use what it wants to use and adapt to that using sizeof.

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