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#include "cuda_runtime.h"

#include "device_launch_parameters.h"

#include <stdio.h>

#define BlockSize  2

#define ThreadSize 10

#define ArraySize (BlockSize*ThreadSize)

__global__ void shared(int* a) //running on device

{

     __shared__ int x[ThreadSize]; //shared in the same block

     int i = blockIdx.x*ThreadSize+threadIdx.x;

     x[threadIdx.x] = a[i]; //copy global to shared memory

     if (threadIdx.x < ThreadSize/2) {

         x[threadIdx.x] = x[threadIdx.x + 1];

     }

     a[i] = x[threadIdx.x];

}

int main() //running on host

{

     int host_a[ArraySize], host_b[ArraySize]; //memory in host

     int *dev_a = 0; //global memory on device

     cudaSetDevice(0); //select a device

     // init array values

     for (int i = 0; i < ArraySize; i++) {

         host_a[i] = i;

         printf("a[%d]=%d ", i, host_a[i]);

         if (i%ThreadSize == ThreadSize-1) printf("\n");

     }

     printf("\n");

     // init device memory array values

     cudaMalloc((void**)&dev_a, ArraySize * sizeof(int));

     cudaMemcpy(dev_a, host_a, ArraySize * sizeof(int), cudaMemcpyHostToDevice);

     // running kernel in parallel

     shared << < BlockSize, ThreadSize >> > (dev_a);

     //copy result back

     cudaMemcpy(host_b, dev_a, ArraySize * sizeof(int), cudaMemcpyDeviceToHost);

     //   waits for the kernel to finish,

     cudaDeviceSynchronize();

     //output

     for (int i = 0; i < ArraySize; i++) {

         printf("b[%d]=%d ", i, host_b[i]);

         if (i%ThreadSize == ThreadSize-1) printf("\n");

     }

     printf("\n");

     getchar(); //wait keypressed

     return 0;

}