ref: 693485e9c4eab63cf46f38783c2e5f8097ae2bc9
dir: /sys/src/libc/port/strcspn.c/
#include <u.h>
#include <libc.h>
#define N 256
long
strcspn(char *s, char *b)
{
char map[N], *os;
memset(map, 0, N);
for(;;) {
map[*(uchar*)b] = 1;
if(*b++ == 0)
break;
}
os = s;
while(map[*(uchar*)s++] == 0)
;
return s - os - 1;
}