使用Intel AVX从压缩双精度向量存储单个双精度 [英] Storing individual doubles from a packed double vector using Intel AVX

问题描述

我正在使用C内在函数编写英特尔AVX指令的代码.如果我有一个压缩的双矢量(__m256d)，那么将每个矢量存储到内存中不同位置的最有效方法(即最少的操作数)是什么(即，我需要将它们散开到另一个位置)使其不再包装的位置)?伪代码:

I'm writing code using the C intrinsics for Intel's AVX instructions. If I have a packed double vector (a __m256d), what would be the most efficient way (i.e. the least number of operations) to store each of them to a different place in memory (i.e. I need to fan them out to different locations such that they are no longer packed)? Pseudocode:

__m256d *src;
double *dst;
int dst_dist;
dst[0] = src[0];
dst[dst_dist] = src[1];
dst[2 * dst_dist] = src[2];
dst[3 * dst_dist] = src[3];

使用SSE，我可以使用_mm_storel_pi和_mm_storeh_pi内部函数对__m128类型执行此操作.我无法找到与AVX类似的任何东西，从而无法将单个64位片段存储到内存中.是否存在?

Using SSE, I could do this with __m128 types using the _mm_storel_pi and _mm_storeh_pi intrinsics. I've not been able to find anything similar for AVX that allows me to store the individual 64-bit pieces to memory. Does one exist?

推荐答案

您可以使用一些提取的解释器来做到这一点:(警告:未经测试)

You can do it with a couple of extract instrinsics: (warning: untested)

 __m256d src = ...  //  data

__m128d a = _mm256_extractf128_pd(src, 0);
__m128d b = _mm256_extractf128_pd(src, 1);

_mm_storel_pd(dst + 0*dst_dist, a);
_mm_storeh_pd(dst + 1*dst_dist, a);
_mm_storel_pd(dst + 2*dst_dist, b);
_mm_storeh_pd(dst + 3*dst_dist, b);

您想要的是AVX2中的收集/分散说明...但这还需要几年的时间.

What you want is the gather/scatter instructions in AVX2... But that's still a few years down the road.

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