SSE中的比较操作

Posted 2023-02-16

【中文标题】SSE中的比较操作

【英文标题】：Comparison operation in SSE

【发布时间】：2014-10-16 10:37:35

【问题描述】：

我是 SSE 编码的新手。我想为我的算法编写一个 SSE 代码。我想把下面的 C 代码转换成 SSE 代码。

for(int i=1;i<height;i++)

    for(int j=1;j<width;j++)
    
        int index = 0;
        if(input[width*i + j]<=input[width*(i-1)+(j-1)])) index += 0x80;
        if(input[width*i + j]<=input[width*(i-1)+(j  )])) index += 0x40;
        if(input[width*i + j]<=input[width*(i-1)+(j+1)])) index += 0x20;
        if(input[width*i + j]<=input[width*(i  )+(j-1)])) index += 0x10;
        if(input[width*i + j]<=input[width*(i  )+(j+1)])) index += 0x08;
        if(input[width*i + j]<=input[width*(i+1)+(j-1)])) index += 0x04;
        if(input[width*i + j]<=input[width*(i+1)+(j  )])) index += 0x02;
        if(input[width*i + j]<=input[width*(i+1)+(j+1)])) index ++;
        output[width*(i-1)+(j-1)] = index;

    

这是我的 SSE 代码：

unsigned char *dst_d = outputbuffer
float *CT_image_0 = inputbuffer;
float *CT_image_1 = CT_image_0 + width;
float *CT_image_2 = CT_image_1 + width; 
for(int i=1;i<height;i++)

    for(int j=1;j<width;j+=4)
    

      __m128 CT_current_00 = _mm_loadu_ps((CT_image_0+j-1));
      __m128 CT_current_10 = _mm_loadu_ps((CT_image_1+j-1));
      __m128 CT_current_20 = _mm_loadu_ps((CT_image_2+j-1));

      __m128 CT_current_01 = _mm_loadu_ps(((CT_image_0+1)+j-1));
      __m128 CT_current_11 = _mm_loadu_ps(((CT_image_1+1)+j-1));
      __m128 CT_current_21 = _mm_loadu_ps(((CT_image_2+1)+j-1));

      __m128 CT_current_02 = _mm_loadu_ps(((CT_image_0+2)+j-1));
      __m128 CT_current_12 = _mm_loadu_ps(((CT_image_1+2)+j-1));
      __m128 CT_current_22 = _mm_loadu_ps(((CT_image_2+2)+j-1));

      __m128 val    =  CT_current_11;

      //Below I tried to write the SSE instruction but that was wrong :( 
      //--How I can do index + ...operation with this _mm_cmple_ss return value ????
      __m128 sample6= _mm_cmple_ss(val,CT_current_00);
       sample6 += _mm_cmple_ss(val,CT_current_01);
       sample6 += _mm_cmple_ss(val,CT_current_02);
       sample6 += _mm_cmple_ss(val,CT_current_10);
       sample6 +=_mm_cmple_ss(val,CT_current_12);
       sample6 +=_mm_cmple_ss(val,CT_current_20);
       sample6 +=_mm_cmple_ss(val,CT_current_21);
       sample6 +=_mm_cmple_ss(val,CT_current_22);
    
    CT_image_0 +=width;
    CT_image_1 +=width;
    CT_image_2 +=width;
    dst_d += (width-2);

我打破了我的头并尝试（作为一个外行）使用 if 条件......请给我一些想法？？？

【参考方案1】：

需要工作的部分显然是这样的：

  __m128 sample6= _mm_cmple_ss(val,CT_current_00);
   sample6 += _mm_cmple_ss(val,CT_current_01);
   sample6 += _mm_cmple_ss(val,CT_current_02);
   sample6 += _mm_cmple_ss(val,CT_current_10);
   sample6 +=_mm_cmple_ss(val,CT_current_12);
   sample6 +=_mm_cmple_ss(val,CT_current_20);
   sample6 +=_mm_cmple_ss(val,CT_current_21);
   sample6 +=_mm_cmple_ss(val,CT_current_22);

您需要将所有比较结果组合成一组标志，例如像这样：

   __m128i out = _mm_setzero_si128();                // init output flags to all zeroes
   __m128i test;

   test = _mm_cmple_ss(val, CT_current_00);          // compare
   test = _mm_and_si128(test, _mm_set1_epi32(0x80)); // mask all but required flag
   out = _mm_or_si128(out, test);                    // merge flags to output mask
   test = _mm_cmple_ss(val, CT_current_01);
   test = _mm_and_si128(test, _mm_set1_epi32(0x40));
   out = _mm_or_si128(out, test);
   // ... repeat for each offset and flag value
   // ... then finally extract 4 bytes from `out`
   // ... and store at output[width*(i-1)+(j-1)]

【参考方案2】：

我不知道 SSE 是什么代码，但您很可能希望运行一个/或某种组合 CT_current 变量组合成一个字符串数组，然后将它们与前面提到的（通过您的代码）连接到一个列表中, CT=** 规范（其中 CT** 是您之后放置的所有内容）；为了迭代回您打印到的 _m128，然后如您所知，您可以在完成后进行两次迭代。

祝你好运。