gistfile1.c

// set bcount somewhere above; assume 0 >= bcount <= 3:
// 
switch (bcount) {
 case 0: mbh = blockIdx.y*2;
         mbw=blockIdx.x*2;
         break;
 case 1: mbh = blockIdx.y*2;
         mbw=blockIdx.x*2+1;
         break;
 case 2: mbh = blockIdx.y*2+1;
         mbw=blockIdx.x*2;
         break;
 case 3: mbh = blockIdx.y*2+1;
         mbw=blockIdx.x*2+1;
         break;
 default: break;
}