Memory access

Hello,
I create a small test program, which is intend to rotate a memory map for 90
degrees.

void Test()
{
#define DX 480
#define DY 640
  WORD *dst,*src;
  src = new WORD[DX*DY];
  dst = new WORD[DX*DY];

  int pxm=DX;
  int pym=DY;
  for(int i=0;i<100;i++) {
    for(int py=0;py<pym;py++) {
      WORD *p1=dst+(py*DX);
      WORD const *p2=src+(pym-py-1);
      for(int px=0; px<pxm; px++) {
        if(px<DY && py<DX) {
          *p1=*p2;
        }
        p1++;
        p2+=DY;
      }
    }
  }
  delete [] dst;
  delete [] src;
}

The problem this is running very slow on Toradex Colibri PXA270 linux
version 2.6.27.
It takes 18seconds to finish it.
If I just replace line *p1=*p2 with *p1=0xff, it takes 490ms.
So my assumpation is that reading of "random" memory is very slow.
I there a way to speed-up such "random" reading?

Many thanks
Erazem