Matrix transpose

1. you have declared B1 and B2 as matrixes of int (then each element is 32 bit in size), but your assembler routine works on 16 bit values, then you should declare your matrixes as short
2. you get and set the matrixes at addresses B, B+8, B+12 and B+16; the right offsets are 0, 8, 16 and 24
3. after the first step you should load again the matrix B1 onto the mm1, mm2, mm3 and mm4 registers

#include <emmintrin.h>
#include <iostream>
#include <iomanip>

using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
   short B1[4][4]; // matrix to be transposed
   short B2[4][4]; // transposed matrix
   
   int n=0;
   for (int i = 0; i < 4; i++)
      for (int j = 0; j < 4; j++, n++)
         B1[i][j] = n;

   __asm{
      movq mm1, B1
      movq mm2, B1+8
      movq mm3, B1+16
      movq mm4, B1+24

      // Step one
      punpcklwd mm1, mm2
      punpcklwd mm3, mm4
      movq mm5, mm1
      punpckldq mm1, mm3
      punpckhdq mm5, mm3

      // Move result to B2 (first two rows)
      movq B2, mm1
      movq B2+8, mm5

      movq mm1, B1
      movq mm2, B1+8
      movq mm3, B1+16
      movq mm4, B1+24

      // Step two
      punpckhwd mm1, mm2
      punpckhwd mm3, mm4
      movq mm5, mm1
      punpckldq mm1, mm3
      punpckhdq mm5, mm3

      // Move result to B2 (last two lines)
      movq B2+16, mm1
      movq B2+24, mm5

      emms
   }


   for (int i = 0; i < 4; i++)
   {
      for (int j = 0; j < 4; j++)
         cout << B1[i][j] << " ";
      cout << endl;
   }

   cout << endl;

   for (int i = 0; i < 4; i++)
   {
      for (int j = 0; j < 4; j++)
         cout << B2[i][j] << " ";
      cout << endl;
   }

   return 0;
}</iomanip></iostream></emmintrin.h>