ref: a314e313bdd65f8f588cc3188df4b215443c03d7
dir: /lib/c/strcspn.c/
#include <string.h>
#undef strcspn
size_t
strcspn(const char *s1, const char *s2)
{
size_t n;
int c;
const char *p;
for (n = 0; c = *s1++; ++n) {
for (p = s2; *p && *p != c; ++p)
;
if (*p == c)
break;
}
return n;
}