ref: 97bfd21a430fbac3267e12e5d67a92a7f5ced8a9
dir: /lib/c/src/strspn.c/
#include <string.h> #undef strspn size_t strspn(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) /* nothing */; if (*p == '\0') break; } return n; }