gistfile1.c

#include <emmintrin.h>
#include <stdio.h>
#include <string.h>

int count(const __m128i *string1, const __m128i *string2, int size)
{
	const int inner_count = 255;
	int max_loop;
	int i, j, r;
	__m128i acc8, acc32, acc32hi, s1, s2, equal, partial, zero;
	
	r = 0;
	max_loop = size/inner_count*inner_count;
	acc32 = zero = _mm_setzero_si128();
	
	for (i = 0; i < max_loop; i = j) {
		acc8 = _mm_set1_epi8(0);
		
		for (j = i; j < i+inner_count; j++) {
			equal = _mm_cmpeq_epi8(string1[j], string2[j]);
			acc8 = _mm_sub_epi8(acc8, equal);
		}
		
		partial = _mm_sad_epu8(acc8, zero);
		acc32 = _mm_add_epi32(acc32, partial);
	}
	
	acc32hi = _mm_srli_si128(acc32, 8);
	acc32 = _mm_add_epi32(acc32, acc32hi);
	r = _mm_cvtsi128_si32(acc32);
	
	return r;		
}

int count_simple(const char *string1, const char *string2, int size)
{
	int r = 0;
	int i;
	for (i = 0; i < size; i++) {
		r += (string1[i] == string2[i]);
	}
	
	return r;
}

#define size 255*1024
union aligned {
	char s[size];
	__m128i v[size/16];
};

int main(void)
{
	union aligned a, b;
		
	FILE *f1 = fopen("data1", "r");
	FILE *f2 = fopen("data2", "r");
	if (fread(a.s, size, 1, f1) < 1)
		return -1;
	if (fread(b.s, size, 1, f2) < 1)
		return -1;
	fclose(f1);
	fclose(f2);
	
	printf("%d\n", count(a.v, b.v, size/16));
	printf("%d\n", count_simple(a.s, b.s, size));
	return 0;
}