ref: 6361c0a2f202ae56f70cb4a7e8b6f45d54abe1e8
dir: /sys/src/libc/port/strspn.c/
#include <u.h>
#include <libc.h>
#define N 256
long
strspn(char *s, char *b)
{
char map[N], *os;
memset(map, 0, N);
while(*b)
map[*(uchar *)b++] = 1;
os = s;
while(map[*(uchar *)s++])
;
return s - os - 1;
}