ref: 8289cfc5ecbb7c27b71861be511701bf94f91f23
dir: /sys/src/libc/port/memchr.c/
#include	<u.h>
#include	<libc.h>
void*
memchr(void *ap, int c, usize n)
{
	uchar *sp;
	sp = ap;
	c &= 0xFF;
	while(n > 0) {
		if(*sp++ == c)
			return sp-1;
		n--;
	}
	return 0;
}