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POFor nested loops with CUDA
 

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  1. POFor nested loops with CUDA
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    <p>I'm having a problem with some for nested loops that I have to convert from C/C++ into CUDA. Basically I have 4 for nested loops which are sharing the same array and making bit shift operations.</p> <pre><code>#define N 65536 // ---------------------------------------------------------------------------------- int a1,a2,a3,a4, i1,i2,i3,i4; int Bit4CBitmapLookUp[16] = {0, 1, 3, 3, 7, 7, 7, 7, 15, 15, 15, 15, 15, 15, 15, 15}; int _cBitmapLookupTable[N]; int s = 0; // index into the cBitmapLookupTable for (i1 = 0; i1 &lt; 16; i1++) { // first customer a1 = Bit4CBitmapLookUp[i1] &lt;&lt; 12; for (i2 = 0; i2 &lt; 16; i2++) { // second customer a2 = Bit4CBitmapLookUp[i2] &lt;&lt; 8; for (i3 = 0; i3 &lt; 16; i3++) { // third customer a3 = Bit4CBitmapLookUp[i3] &lt;&lt; 4; for (i4 = 0;i4 &lt; 16;i4++) { // fourth customer a4 = Bit4CBitmapLookUp[i4]; // now actually set the sBitmapLookupTable value _cBitmapLookupTable[s] = a1 | a2 | a3 | a4; s++; } // for i4 } // for i3 } // for i2 } // for i1 </code></pre> <p>This is the code that I should convert into CUDA. I tried different ways but everytime i having the wrong output. Here i post my version of CUDA conversion (the piece from kernel's part)</p> <pre><code>#define N 16 //---------------------------------------------------------------------------------- // index for the GPU int i1 = blockDim.x * blockIdx.x + threadIdx.x; int i2 = blockDim.y * blockIdx.y + threadIdx.y; int i3 = i1; int i4 = i2; __syncthreads(); for(i1 = i2 = 0; i1 &lt; N, i2 &lt; N; i1++, i2++) { // first customer a1 = Bit4CBitmapLookUp_device[i1] &lt;&lt; 12; // second customer a2 = Bit4CBitmapLookUp_device[i2] &lt;&lt; 8; for(i3 = i4 = 0; i3 &lt; N, i4 &lt; N; i3++, i4++){ // third customer a3 = Bit4CBitmapLookUp_device[i3] &lt;&lt; 4; // fourth customer a4 = Bit4CBitmapLookUp_device[i4]; // now actually set the sBitmapLookupTable value _cBitmapLookupTable[s] = a1 | a2 | a3 | a4; s++; } } </code></pre> <p>I'm brand new in CUDA and I'm still learning, but really i can't find a solution for those for nested loops. Thank you in advance.</p>
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    1. COHint: you're initializing the variables `i1`...`i4` to values that never get used.
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    2. COSee this -> http://stackoverflow.com/questions/5306117/cuda-kernel-nested-for-loop http://stackoverflow.com/questions/6479715/nested-loops-to-cuda http://stackoverflow.com/questions/9527026/cumulative-sum-in-two-dimensions-on-array-in-nested-loop-cuda-implementation
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