Nested loop in GLSL causes driver crash.

[Aethanol]

Hello,

I'm trying to write an image fusion program in OpenGL/GLSL. At one point I need to calculate a cumulated histogram for a 7x7 pixel area. In fragment shader I'm trying to use a function:

float graythresh(float aArea[49])
  {
  float hist[256];
  for(int i = 0; i < 49; i++)
    hist[(int)(aArea[i]*255)]+= 1.0;
 
  for(int i = 0; i < 256; i++)
    hist[i] /= 49.0;
 
  for(int i = 255; i >= 0; i--)
    for(int j = 255; j >= 0; j--)
      if(j > i)
        hist[i] += hist[j];
 
  return 0.0;
  }

The last loop causes application crash and error "driver stopped responding". I tried using older drivers, and testing the application on different computer, nothing changed.

  for(int i = 255; i >= 0; i--)
    for(int j = i-1; j >= 0; j--)
        hist[i] += hist[j];

Gave same error. Is it even possible to this?

Thanks in Advance, any help will be appreciated.

(I'm using GeForce GT 420M, windows 7)