ref: b03ae0993b8b96e340e560f9f649fc6c8b2b8081
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;
}