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我有這樣的功能代碼:未對齊的對齊指針上的訪問?
bool interpolate(const Mat &im, float ofsx, float ofsy, float a11, float a12, float a21, float a22, Mat &res)
{
bool ret = false;
// input size (-1 for the safe bilinear interpolation)
const int width = im.cols-1;
const int height = im.rows-1;
// output size
const int halfWidth = res.cols >> 1;
const int halfHeight = res.rows >> 1;
float *out = res.ptr<float>(0);
const float *imptr = im.ptr<float>(0);
for (int j=-halfHeight; j<=halfHeight; ++j)
{
const float rx = ofsx + j * a12;
const float ry = ofsy + j * a22;
#pragma omp simd
for(int i=-halfWidth; i<=halfWidth; ++i, out++)
{
float wx = rx + i * a11;
float wy = ry + i * a21;
const int x = (int) floor(wx);
const int y = (int) floor(wy);
if (x >= 0 && y >= 0 && x < width && y < height)
{
// compute weights
wx -= x; wy -= y;
int rowOffset = y*im.cols;
int rowOffset1 = (y+1)*im.cols;
// bilinear interpolation
*out =
(1.0f - wy) * ((1.0f - wx) * imptr[rowOffset+x] + wx * imptr[rowOffset+x+1]) +
( wy) * ((1.0f - wx) * imptr[rowOffset1+x] + wx * imptr[rowOffset1+x+1]);
} else {
*out = 0;
ret = true; // touching boundary of the input
}
}
}
return ret;
}
這是與icpc
編譯代碼部分,以下選項:
INTEL_OPT=-O3 -simd -xCORE-AVX2 -parallel -qopenmp -fargument-noalias -ansi-alias -no-prec-div -fp-model fast=2 -fma -align -finline-functions
INTEL_PROFILE=-g -qopt-report=5 -Bdynamic -shared-intel -debug inline-debug-info -qopenmp-link dynamic -parallel-source-info=2 -ldl
在優化報告文件(.optr
)有這些行:
remark #15389: vectorization support: reference *out has unaligned access [ /home/luca/Dropbox/HKUST/CloudCache/cloudcache/CloudCache/Descriptors/hesaff/helpers.cpp(259,14) ]
remark #15389: vectorization support: reference *out has unaligned access [ /home/luca/Dropbox/HKUST/CloudCache/cloudcache/CloudCache/Descriptors/hesaff/helpers.cpp(263,14) ]
remark #15389: vectorization support: reference *out has unaligned access [ /home/luca/Dropbox/HKUST/CloudCache/cloudcache/CloudCache/Descriptors/hesaff/helpers.cpp(263,14) ]
線259和263是其中明顯out
值被改變的人。
據我所知,這意味着out
是unaligned(更多信息在這裏[https://software.intel.com/en-us/articles/fdiag15126]和here)。
但是,這已經很奇怪,因爲我發現它here,cv::Mat
對象已經對齊。但是,這可能是合法的,因爲編譯器會不知道對齊的...... 如果我專門分配out
作爲對齊指針,如果我添加下面一行然而出現的消息:
out = (float*) _mm_malloc(res.cols*res.rows*sizeof(float), 32);
這應該是足夠的告訴編譯器數據是對齊的。我錯了嗎?否則,我怎麼能告訴它,out
已經對齊?
謝謝您的回答。所以假設我使用的是一臺可以同時處理8個浮點元素的AVX2機器,我應該在一個迭代循環中計算8個值,然後在'for'子句中執行'out + = 8'嗎?如果我沒有錯,這是循環展開,這是由編譯器自動完成的。我錯過了什麼? – justHelloWorld
(你可以看看[this](http://stackoverflow.com/questions/43778590/ineffective-remainder-loop-in-my-code)的問題嗎?) – justHelloWorld