src/string/strspn.c

   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 }