1#include <string.h>
 2
 3#define BITOP(a,b,op) \
 4 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
 5
 6size_t strcspn(const char *s, const char *c)
 7{
 8	const char *a = s;
 9	size_t byteset[32/sizeof(size_t)];
10
11	if (!c[0] || !c[1]) return __strchrnul(s, *c)-a;
12
13	memset(byteset, 0, sizeof byteset);
14	for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
15	for (; *s && !BITOP(byteset, *(unsigned char *)s, &); s++);
16	return s-a;
17}