github.com/afumu/libc@v0.0.6/musl/src/string/strspn.c (about)

     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  }