ref: 8e56bd06b559b45d6a8544ae2b1f752a5b3da516
dir: /sys/src/ape/lib/ap/gen/strcspn.c/
#include <string.h>
#define N 256
size_t
strcspn(const char *s, const char *b)
{
char map[N], *os;
memset(map, 0, N);
for(;;) {
map[*(unsigned char*)b] = 1;
if(*b++ == 0)
break;
}
os = (char*)s;
while(map[*(unsigned char*)s++] == 0)
;
return s - os - 1;
}