strspn.c raw

   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  
   6  size_t strspn(const char *s, const char *c)
   7  {
   8  	const char *a = s;
   9  	size_t byteset[32/sizeof(size_t)] = { 0 };
  10  
  11  	if (!c[0]) return 0;
  12  	if (!c[1]) {
  13  		for (; *s == *c; s++);
  14  		return s-a;
  15  	}
  16  
  17  	for (; *c && BITOP(byteset, *(unsigned char *)c, |=); c++);
  18  	for (; *s && BITOP(byteset, *(unsigned char *)s, &); s++);
  19  	return s-a;
  20  }
  21