g ++中缺少AVX日志内在函数（_mm256_log_ps） - 4.8？ [英] AVX log intrinsics (_mm256_log_ps) missing in g++-4.8?

问题描述

我试图在我的代码中使用一些AVX内在函数，并遇到了对数内在函数的砖墙。

I am trying to utilise some AVX intrinsics in my code and have run into a brick wall with the logarithm intrinsics.

使用英特尔Intrinsics指南v3.0.1 Linux，我看到内在的 _mm256_log_ps（__ m256）被列为immintrin.h的一部分，并且也支持我当前的arch。

Using the Intel Intrinsics Guide v3.0.1 for Linux, I see the intrinsic _mm256_log_ps(__m256) listed as being part of "immintrin.h" and also supported on my current arch.

但是试图编译这个简单的测试用例失败，error：'_mm256_log_ps'没有在这个范围内声明

However trying to compile this simple test case fails with "error: ‘_mm256_log_ps’ was not declared in this scope"

code> g ++ - 4.8 -march = native -mavx test.cpp

The example was compiled with g++-4.8 -march=native -mavx test.cpp

#include <immintrin.h>
int main()
{
        __m256 i;
        _mm256_log_ps(i);
}

我缺少一些基本的东西吗？ g ++是否支持某些内在函数，并且仅在icc中可用？

Am I missing something fundamental here? Are certain intrinsics not supported by g++ and only available in icc?

解决方案：此指令不是真正的内在，而是作为ICC的Intel SVML的一部分实现。 / p>

SOLVED: This instruction is not a true intrinsic but instead implemented as part of the Intel SVML for ICC.

推荐答案

如您对问题的评论中所示，该内在函数不映射到实际的AVX指令;它是对内在集的Intel扩展。该实现可能使用许多基本指令，因为对数不是微不足道的操作。

As indicated in the comments to your question, that intrinsic doesn't map to an actual AVX instruction; it is an Intel extension to the intrinsic set. The implementation likely uses many underlying instructions, as a logarithm isn't a trivial operation.

如果您想要使用非英特尔的编译器，但想要一个快速的对数实现，您可以查看此开源实现 sin（）， cos（）， exp（）和 log（）函数。它们基于之前具有相同功能的 SSE2版本。

If you'd like to use a non-Intel compiler but want a fast logarithm implementation, you might check out this open-source implementation of sin(), cos(), exp(), and log() functions using AVX. They are based on an earlier SSE2 version of the same functions.

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