Super simple single-header bitarray example in C

bitarray.h

// Simple bitarray example
// -----------------------
// Warning: no bounds checking
// Usually I'd use 'uint8_t' instead of an 'char' and 'size_t' instead of an 'int',
//  but this way it can be copied anywhere without worrying about includes.

static inline int bitarray_get(const char* bitarray, const int index) {
    return ((bitarray[index / 8]) >> (index % 8)) & 1;
}

static inline void bitarray_set1(char* bitarray, const int index) {
    bitarray[index / 8] |= (1 << (index % 8));
}

static inline void bitarray_set0(char* bitarray, const int index) {
    bitarray[index / 8] &= ~(1 << (index % 8));
}

// Note: the compiler is good at optimizing the bitwise math used in this example.
// 'bitarray_get' function would be optimized into something like this:
// return ((bitarray[index >> 3]) >> (index & 7)) & 1;
// This works on Clang and GCC even without optimizations disabled.