Find the first non-repeated character in a string

get_first_unique_char.c

#include <stdlib.h>

unsigned char* get_first_unique_char(unsigned char* str, const int len) {
	int pos[256] __attribute__ ((__aligned__(64))), i, p;
	if (str == NULL || len <= 0)
		return NULL;
	for (i=0; i<256; i++)
		pos[i] = -1;
	for (i=0; i<len; i++)
		pos[str[i]] = ( pos[str[i]] == -1 ? i : -2 );
	for (i=0, p=len; i<256; i++)
		p = ( pos[i] >= 0 && pos[i] < p ? pos[i] : p );
	return p==len ? NULL : str+p;
}