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 6size_t strspn(const char* s, const char* c) { 7 const char* a = s; 8 size_t byteset[32 / sizeof(size_t)] = {}; 9 10 if (!c[0]) 11 return 0; 12 if (!c[1]) { 13 for (; *s == *c; s++) 14 ; 15 return s - a; 16 } 17 18 for (; *c && BITOP(byteset, *(unsigned char*)c, |=); c++) 19 ; 20 for (; *s && BITOP(byteset, *(unsigned char*)s, &); s++) 21 ; 22 return s - a; 23} 24