ref: f510f5f6eaa66e5f6a399f6bc4fa7091e00a6151
dir: /bitvector.h/
uint32_t *bitvector_resize(uint32_t *b, uint64_t oldsz, uint64_t newsz, int initzero);
#define bitvector_new(n, initzero) bitvector_resize(nil, 0, (n), (initzero))
#define bitvector_nwords(nbits) (((uint64_t)(nbits)+31)>>5)
#define bitvector_get(b, n) (b[(n)>>5] & (1U<<((n)&31)))
#define bitvector_set(b, n) do{ \
b[(n)>>5] |= 1U<<((n)&31); \
}while(0)
#define bitvector_reset(b, n) do{ \
b[(n)>>5] &= ~(1U<<((n)&31)); \
}while(0)