I have two vectors of 4 integers each and I'd like to use a SIMD command to compare them (say generate a result vector where each entry is 0 or 1 according to the result of the comparison).
Then, I'd like to compare the result vector to a vector of 4 zeros and only if they're equal do something.
Do you know what SIMD commands I can use to do it?
To compare two SIMD vectors:
#include <stdint.h>
#include <xmmintrin.h>
int32_t __attribute__ ((aligned(16))) vector1[4] = { 1, 2, 3, 4 };
int32_t __attribute__ ((aligned(16))) vector2[4] = { 1, 2, 2, 2 };
int32_t __attribute__ ((aligned(16))) result[4];
__m128i v1 = _mm_load_si128((__m128i *)vector1);
__m128i v2 = _mm_load_si128((__m128i *)vector2);
__m128i vcmp = _mm_cmpeq_epi32(v1, v2);
_mm_store_si128((__m128i *)result, vcmp);
Notes:
vector1
, vector2
, result
all need to be 16 byte aligned{ -1, -1, 0, 0 }
for above code example)UPDATE
If you just want a single Boolean result for the case where all 4 elements match then you can do it like this:
#include <stdint.h>
#include <xmmintrin.h>
int32_t __attribute__ ((aligned(16))) vector1[4] = { 1, 2, 3, 4 };
int32_t __attribute__ ((aligned(16))) vector2[4] = { 1, 2, 2, 2 };
__m128i v1 = _mm_load_si128((__m128i *)vector1);
__m128i v2 = _mm_load_si128((__m128i *)vector2);
__m128i vcmp = _mm_cmpeq_epi32(v1, v2);
uint16_t mask = _mm_movemask_epi8(vcmp);
int result = (mask == 0xffff);