1#define _GNU_SOURCE
2#include <string.h>
3
4#define BITOP(a,b,op) \
5 ((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
6
7size_t strcspn(const char *s, const char *c)
8{
9	const char *a = s;
10	size_t byteset[32/sizeof(size_t)];
11
12	if (!c[0] || !c[1]) return strchrnul(s, *c)-a;
13
14	memset(byteset, 0, sizeof byteset);
15	for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
16	for (; *s && !BITOP(byteset, *(unsigned char *)s, &); s++);
17	return s-a;
18}
19