ref: d9cfe3ba586178478b6d89751132b7767b7e17af
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; }