ref: 0092ca7b1aa047ca72d308c6f682097fd1f7c806
dir: /sys/src/ape/lib/ap/gen/memchr.c/
#include	<string.h>
void*
memchr(const void *ap, int c, size_t n)
{
	unsigned char *sp;
	sp = ap;
	c &= 0xFF;
	while(n > 0) {
		if(*sp++ == c)
			return sp-1;
		n--;
	}
	return 0;
}