Function fb_init

BeefRT/JEMalloc/include/jemalloc/internal/fb.h:17–21

    + ((nbits) % FB_GROUP_BITS == 0 ? 0 : 1))

static inline void
fb_init(fb_group_t *fb, size_t nbits) {
	size_t ngroups = FB_NGROUPS(nbits);
	memset(fb, 0, ngroups * sizeof(fb_group_t));
}

static inline bool
fb_empty(fb_group_t *fb, size_t nbits) {