向MMX内联汇编中的数组元素添加常量

问题描述

如何为每个数组元素添加一个常量?
请参见下面的代码段:

How do I add a constant to each array elements?
See code snippet below:

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include "xmmintrin.h"
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
    int x[4][4]={1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4}; //source or input
    int y[4][4];//destination or output
    int b[4] ={5,5,5,5};// constant
    int f0,f1,f2,f3;
    __asm
    {
    mov eax,x
    mov ecx,b
    mov edi,y
        //stage one
    movq mm0,[eax]
    movq mm7,[ecx]
    paddw mm0,mm7
    movq [f0],mm0
    movq mm1,[eax+8]
    paddw mm1,mm7
    movq [f1],mm1
    movq mm2,[eax+16]
    paddw mm2,mm7
    movq [f2],mm2
    movq mm3,[eax+24]
    paddw mm3,mm7
    movq [f3],mm3
    //stage two

    movq mm0,[f0]
    psraw mm0,6
    movq [edi],mm0
    movq mm1,[f1]
    psraw mm1,6
    movq [edi+8],mm1
    movq mm2,[f2]
    psraw mm2,6
    movq [edi+16],mm2
    movq mm3,[f3]
    psraw mm3,6
    movq [edi+24],mm3

    }
for (int i = 0; i < 4; i++)
       {
          for (int j = 0; j < 4; j++)
             cout << y[i][j] << " ";
          cout << endl;
       }
    return 0;
}

推荐答案

int _tmain(int argc, _TCHAR* argv[])
{
    int x[4][4]={1,2,3,4,2,2,2,2,3,3,3,3,4,4,4,4}; //source or input
    int y[4][4];//destination or output
    int b[4] ={5,5,5,5}; // constant
    //int f0,f1,f2,f3;

    __asm
    {
        push    esi
        push    edi
        push    ebx

        lea     esi, x
        lea     edi, y
        lea     edx, b
        //stage one

        mov     eax, 4
        mov     ebx, eax        ; mov   ebx, 1st dim size
_loop_00:
        mov     ecx, eax        ; mov   ecx, 2nd dim size
_loop_01:
        movd    mm0, [edx]
        movd    mm1, [esi]
        paddd   mm0, mm1
        ; psraw mm0, 6           ; // stage two
        movd    [edi], mm0
        add     esi, eax
        add     edi, eax
        loop    _loop_01
        add     edx, eax
        dec     ebx
        jnz     _loop_00

        //stage two
        // ???

        pop     ebx
        pop     edi
        pop     esi
    }

    _mm_empty();

    for (int i = 0; i < 4; i++)
    {
        for (int j = 0; j < 4; j++)
            cout << y[i][j] << " ";
        cout << endl;
    }
    return 0;
}

我不明白第二阶段.我将其注释掉是因为它产生的所有0都具有如此小的值. :-)如果需要进行算术移位，则可以取消注释行; psraw mm0，6".

您还可以通过ebx和ecx更改数组大小.我已使用eax寄存器，因为所有常量值均等于4，以进行优化(在这种情况下).

顺便说一句，我已经使用MMX代表您问题的标题.在不使用MMX指令集的情况下，将有一些更优化的方式(仅使用x86).因为数组元素是"int"(即32位)，所以我认为使用64位MMX寄存器不会带来任何收益.

I didn''t understand stage two. I commented it out because it yields all 0 with such small values. :-) If you need to do arithmetic shift, you can un-comment line "; psraw mm0, 6".

You can also change array sizes by ebx and ecx. I''ve used eax register as all constant values equal 4 for optimization (in this particular case).

BTW, I''ve used MMX on behalf of your question''s title. There would be some more optimized (using only x86) way of doing this without using MMX instruction set. Because array elements are "int" (that is, 32 bits), I think, there is no gain by using 64 bits MMX registers.

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