#include <cuda.h>
// kernel
__global__ void sub1(float* fx, float* fy, float* fe) {
#define BLOCK (512)
int t = threadIdx.x; // builtin
int b = blockIdx.x; // builtin
float e;
__shared__ float se[BLOCK];
__shared__ float sx[BLOCK];
__shared__ float sy[BLOCK+2];
// copy from device to processor memory
sx[t] = fx[BLOCK*b+t];
sy[t] = fy[BLOCK*b+t];
if (t<2)
sy[t+BLOCK] = fy[BLOCK*b+t+BLOCK];
__syncthreads();
// do computation
sx[t] += ( sy[t+2] + sy[t] )*.5;
e = sy[t+1] * sy[t+1];
// copy to device memory
fx[BLOCK*b+t] = sx[t];
// reduction
se[t] = e;
__syncthreads();
if (t<256) {
se[t] += se[t+256];
__syncthreads();
}
if (t<128) {
se[t] += se[t+128];
__syncthreads();
}
if (t<64) {
se[t] += se[t+64];
__syncthreads();
}
if (t<32) { // warp size
se[t] += se[t+32];
se[t] += se[t+16];
se[t] += se[t+8];
se[t] += se[t+4];
se[t] += se[t+2];
se[t] += se[t+1];
}
if (t==0)
fe[b] = se[0];
}
int main(int argc, char *argv[]) {
int n = ...;
float *x, *y;
x = new float[n+1];
y = new float[n+1];
... // fill x, y
// allocate GPU memory
float *fx, *fy, *fe;
cudaMalloc((void**)&fx, (n-1+2) * sizeof(float));
cudaMalloc((void**)&fy, (n-1+2) * sizeof(float));
cudaMalloc((void**)&fe, (n-1+2)/BLOCK * sizeof(float));
float *de = new float[(n-1+2)/BLOCK];
// copy to GPU memory
cudaMemcpy(fx+1, &x[1],
(n-1) * sizeof(float), cudaMemcpyHostToDevice);
cudaMemcpy(fy, &y[1-1],
(n-1+2) * sizeof(float), cudaMemcpyHostToDevice);
dim3 dimBlock(BLOCK, 1, 1);
dim3 dimGrid((n-1+2)/BLOCK, 1, 1);
float e = 0;
// call GPU
sub1<<<dimGrid, dimBlock>>>(fx, fy, fe);
// copy to host memory
cudaMemcpy(fx+1, &x[1], (n-1) * sizeof(float),
cudaMemcpyDeviceToHost);
cudaMemcpy(fe, &de[1-1], (n-1+2)/BLOCK * sizeof(float),
cudaMemcpyDeviceToHost);
// release GPU memory
cudaFree(fe);
cudaFree(fy);
cudaFree(fx);
float e_local = 0;
for (int i=0; i<(n-1+2)/BLOCK; ++i)
e_local += de[i];
e += e_local;
delete[] de;
... // output x, e
delete[] x, y;
return 0;
}
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