CUDAのblock,gridの計算をファイル出力してみる

#include "cuda_runtime.h"
#include "device_launch_parameters.h"

#include <stdio.h>
#include <stdlib.h>

///////////////////////////////////////////////
// GPU側 ////////////////////////////////////// 
__global__ void threadpos(
  unsigned char* c,
  const int width,
  const int height) {

  //アクセス法
  //このスレッドが担当する画素の位置を二次元座標で求める
  size_t xpos = blockIdx.x * blockDim.x + threadIdx.x;
  size_t ypos = blockIdx.y * blockDim.y + threadIdx.y;

  if (xpos >= width || ypos >= height)return;

  int pos = ypos * width + xpos;

  c[pos * 6 + 0] = blockIdx.x;
  c[pos * 6 + 1] = blockIdx.y;
  c[pos * 6 + 2] = threadIdx.x;
  c[pos * 6 + 3] = threadIdx.y;
  c[pos * 6 + 4] = xpos;
  c[pos * 6 + 5] = ypos;

}
/////

int main()
{
  int width = 10;
  int height = 10;
  int item = 6;


  // 最小単位 合計で512未満
  //5×5の領域に分けて計算する
  dim3 block(5, 5);

  //グリッド数
  dim3 grid(2, 2);

  unsigned char* p_cpu = new unsigned char[width*height*item];
  for (int i = 0; i < width*height*item; i++) {
    p_cpu[i] = 0;
  }

  unsigned char* p_gpu;//GPU側メモリ確保
  cudaMalloc((void**)&p_gpu, width*height * item);
  threadpos << <grid, block >> > (p_gpu, width,height);

  //GPU→CPU側へメモリコピー
  cudaMemcpy(p_cpu, p_gpu, width*height * item, cudaMemcpyDeviceToHost);
  cudaFree(p_gpu);

  
  ///////////////////////////////////////////////
  // 結果出力

  FILE* fpblock = fopen("block.txt", "w");
  FILE* fpthread = fopen("thread.txt", "w");
  FILE* fpxy = fopen("xy.txt", "w");
  for (size_t y = 0; y < height; y++) {
    for (size_t x = 0; x < width; x++) {
      int pos = y * width + x;

      fprintf(fpblock,"[%2d %2d]",
        p_cpu[pos * item + 0],
        p_cpu[pos * item + 1]
      );
      fprintf(fpthread, "[%2d %2d]",
        p_cpu[pos * item + 2],
        p_cpu[pos * item + 3]
      );
      fprintf(fpxy, "(%2d %2d)",
        p_cpu[pos * item + 4],
        p_cpu[pos * item + 5]
      );

    }
    fprintf(fpblock,"\n");
    fprintf(fpthread, "\n");
    fprintf(fpxy, "\n");
  }
  fclose(fpblock);
  fclose(fpthread);
  fclose(fpxy);

  delete[] p_cpu;

    return 0;
}