Question

I made a kernel:

__kernel void square(                                                       
   __global uchar* input,                                             
   __global uchar* output,                                           
   const unsigned int count)                                       
{                                                                      
   int i = get_global_id(0);                                           
   if(i < count)                                                      
       output[i] = input[i] * input[i];                                
}; 

The output from my program is, input matrix and output listed. I see that all work items evaluated to val*val % 256. Why ?

Found 1 platform(s).
OutData from Write and Read:
0
[91, 2, 79, 179, 52, 205, 236, 8;
  181, 239, 26, 248, 207, 218, 45, 183;
  158, 101, 102, 18, 118, 68, 210, 139;
  198, 207, 211, 181, 162, 197, 191, 196;
  40, 7, 243, 230, 45, 6, 48, 173;
  242, 125, 175, 90, 63, 90, 22, 112;
  221, 167, 224, 113, 208, 123, 214, 35;
  229, 6, 143, 138, 98, 81, 118, 187;
  167, 140, 218, 178, 23, 43, 133, 154;
  150, 76, 101, 8, 38, 238, 84, 47]
[89, 4, 97, 41, 144, 41, 144, 64;
  249, 33, 164, 64, 97, 164, 233, 209;
  132, 217, 164, 68, 100, 16, 68, 121;
  36, 97, 233, 249, 132, 153, 129, 16;
  64, 49, 169, 164, 233, 36, 0, 233;
  196, 9, 161, 164, 129, 164, 228, 0;
  201, 241, 0, 225, 0, 25, 228, 201;
  217, 36, 225, 100, 132, 161, 100, 153;
  241, 144, 164, 196, 17, 57, 25, 164;
  228, 144, 217, 64, 164, 68, 144, 161]


OutData from Write and Read:
8913
Succed
Press any key to continue . . .

Answer 1

The answer is that the operation overflows on the GPU and when using uchar type, 256 becomes 0 again and the cycle continues.