square.cu

#include <stdio.h>
#include <cuda.h>

// Kernel that executes on the CUDA device
__global__ void square_array(float *a, int N)
{
    int idx = blockIdx.x * blockDim.x + threadIdx.x;
    if (idx<N) a[idx] = a[idx] * a[idx];
}

// main routine that executes on the host
int main(void)
{
    float *a_h, *a_d;  // Pointer to host & device arrays
    const int N = 10;  // Number of elements in arrays
    size_t size = N * sizeof(float);
    a_h = (float *)malloc(size);        // Allocate array on host
    cudaMalloc((void **)&a_d, size);   // Allocate array on device
                                       // Initialize host array and copy it to CUDA device
    for (int i = 0; i<N; i++) a_h[i] = (float)i;
    cudaMemcpy(a_d, a_h, size, cudaMemcpyHostToDevice);
    // Do calculation on device:
    int block_size = 4;
    int n_blocks = N / block_size + (N%block_size == 0 ? 0 : 1);
    square_array << < n_blocks, block_size >> > (a_d, N);
    // Retrieve result from device and store it in host array
    cudaMemcpy(a_h, a_d, sizeof(float)*N, cudaMemcpyDeviceToHost);
    // Print results
    for (int i = 0; i<N; i++) printf("%d %f\n", i, a_h[i]);
    // Cleanup
    free(a_h); cudaFree(a_d);
}