Extracting ints and shorts from a structure using AVX?
I have a structure that contains a concatenation between various items and an AVX type to load all bytes into one load. My code looks like this:
#include <immintrin.h>
union S{
struct{
int32_t a;
int32_t b;
int16_t c;
int16_t d;
};
__m128i x;
}
I would like to use the AVX register to load data together and then separately extract the four members into local variables int32_t
and int16_t
.
How should I do it? I'm not sure how can I separate the data from each other when retrieving from the AVX register?
EDIT: Looking for answers in terms of GCC builtins.
EDIT2: updated the code to change the structure using union.
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You can extract 16-bit elements from __m128i
with _mm_extract_epi16
(requires SSE2):
int16_t v = _mm_extract_epi16 (v, 4); // extract element 4
For 32-bit elements use _mm_extract_epi32
(requires SSE4.1)
int32_t v = _mm_extract_epi32 (v, 0); // extract element 0
Assuming your structure is declared as:
union S{
struct{
int32_t a;
int32_t b;
int16_t c;
int16_t d;
};
__m128i x;
}
then you will extract the elements a, b, c, d like this:
S s = { { 1, 2, 3, 4 } };
__m128i v = _mm_loadu_si128((__m128i *)&s);
int32_t a = _mm_extract_epi32 (v, 0);
int32_t b = _mm_extract_epi32 (v, 1);
int16_t c = _mm_extract_epi16 (v, 4);
int16_t d = _mm_extract_epi16 (v, 5);
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