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#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 strspn(const char *_s, const char *_c)
{
const unsigned char *s = _s;
const unsigned char *c = _c;
const unsigned char *a = s;
size_t byteset[32/sizeof(size_t)] = { 0 };
if (!c[0]) return 0;
if (!c[1]) {
for (; *s == *c; s++);
return s-a;
}
for (; *c && BITOP(byteset, *c, |=); c++);
for (; *s && BITOP(byteset, *s, &); s++);
return s-a;
}
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