#define _DEFAULT_SOURCE#include <string.h>#define BITOP(a,b,op) \((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))size_t strcspn(const char *s, const char *c){const char *a = s;size_t byteset[32/sizeof(size_t)];if (!c[0] || !c[1]) return strchrnul(s, *c)-a;memset(byteset, 0, sizeof byteset);for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);for (; *s && !BITOP(byteset, *(unsigned char *)s, &); s++);return s-a;}