AVX指令集

Mar 3rd, 2019 0

这里简要介绍AVX指令集的一些基本指令，可以通过调用C++的库函数实现SIMD。

历史

MME, 1996
SSE, 1999
AVX, 2008
AVX2, 2011

数据类型

Data Type	Description
`__m128`	128-bit vector containing 4 floats
`__m128d`	128-bit vector containing 2 doubles
`__m128i`	128-bit vector containing integers
`__m256`	256-bit vector containing 8 floats
`__m256d`	256-bit vector containing 4 doubles
`__m256i`	256-bit vector containing integers

integers can be chars, shorts, ints, or longs

函数命名规范(naming conventions)

_mm<bit_width>_<name>_<data_type>

<bit_width>: the return size, 128 - empty, 256 - 256
<name>: describes the operation performed by the intrinsic
<data_type>: the function’s primary arguments

Instructions	Description
ps	packed single-precision
pd	packed double-precision
epi8/epi16/epi32/epi64	signed integers
epu8/epu16/epu32/epu64	unsigned integers
si128/si256	unspecified vector
m128/m128i/m128d m256/m256i/m256d	input vector types

举例：_mm256_srlv_epi64 64-bit signed int -> 256-bit vector

完整例子

#include <immintrin.h>
#include <stdio.h>

int main() {

    /* Initialize the two argument vectors */
    __m256 evens = _mm256_set_ps(2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0);
    __m256 odds = _mm256_set_ps(1.0, 3.0, 5.0, 7.0, 9.0, 11.0, 13.0, 15.0);

    /* Compute the difference between the two vectors */
    __m256 result = _mm256_sub_ps(evens, odds);

    /* Display the elements of the result vector */
    float* f = (float*) &result; // type conversion
    printf("%f %f %f %f %f %f %f %f\n",
      f[0], f[1], f[2], f[3], f[4], f[5], f[6], f[7]);

    return 0;
}