如何分配16byte内存对齐的数据 [英] How to allocate 16byte memory aligned data
问题描述
我想实现在一张code对,我需要我的一维数组是16字节的存储对齐SSE矢量化。不过,我已经尝试了几种办法来分配16byte内存对齐的数据,但它最终被4字节的内存对齐。
I am trying to implement SSE vectorization on a piece of code for which I need my 1D array to be 16 byte memory aligned. However, I have tried several ways to allocate 16byte memory aligned data but it ends up being 4byte memory aligned.
我与英特尔编译器国际刑事法院的工作。
这是一个示例code我与测试:
I have to work with the Intel icc compiler. This is a sample code I am testing with:
#include <stdio.h>
#include <stdlib.h>
void error(char *str)
{
printf("Error:%s\n",str);
exit(-1);
}
int main()
{
int i;
//float *A=NULL;
float *A = (float*) memalign(16,20*sizeof(float));
//align
// if (posix_memalign((void **)&A, 16, 20*sizeof(void*)) != 0)
// error("Cannot align");
for(i = 0; i < 20; i++)
printf("&A[%d] = %p\n",i,&A[i]);
free(A);
return 0;
}
这是输出我得到:
&A[0] = 0x11fe010
&A[1] = 0x11fe014
&A[2] = 0x11fe018
&A[3] = 0x11fe01c
&A[4] = 0x11fe020
&A[5] = 0x11fe024
&A[6] = 0x11fe028
&A[7] = 0x11fe02c
&A[8] = 0x11fe030
&A[9] = 0x11fe034
&A[10] = 0x11fe038
&A[11] = 0x11fe03c
&A[12] = 0x11fe040
&A[13] = 0x11fe044
&A[14] = 0x11fe048
&A[15] = 0x11fe04c
&A[16] = 0x11fe050
&A[17] = 0x11fe054
&A[18] = 0x11fe058
&A[19] = 0x11fe05c
这是4字节对齐每次,我都用了memalign可,POSIX memalign可。由于我在Linux上工作,我不能用_mm_malloc无论是我可以用_aligned_malloc。
我得到一个内存破坏错误,当我尝试使用_aligned_attribute(这是适用于单独的gcc我认为)。
It is 4byte aligned everytime, i have used both memalign, posix memalign. Since I am working on Linux, I cannot use _mm_malloc neither can I use _aligned_malloc. I get a memory corruption error when I try to use _aligned_attribute (which is suitable for gcc alone I think).
谁能帮助我准确地生成16byte对齐内存在Linux平台上的ICC数据。
Can anyone assist me in accurately generating 16byte memory aligned data for icc on linux platform.
推荐答案
在分配的内存是对齐的16字节。请参阅:结果&安培; A [0] = 0x11fe010
结果
但在浮动
,每个元素都是4个字节,所以第二个是4字节对齐。结果
The memory you allocate is 16-byte aligned. See:
&A[0] = 0x11fe010
But in an array of float
, each element is 4 bytes, so the second is 4-byte aligned.
您可以使用结构数组,每个包含一个单一的浮动,与对齐
属性:
You can use an array of structures, each containing a single float, with the aligned
attribute:
struct x {
float y;
} __attribute__((aligned(16)));
struct x *A = memalign(...);
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