cuda做点乘

#include "cuda_runtime.h"
#include "cublas_v2.h"
#include "time.h"
#include <iostream>

using namespace std;

#define imin(a,b) (a<b?a:b)
const int N = 31 * 1024;
const int threadsPerBlock = 256;
const int blocksperGrid = imin(32, (N + threadsPerBlock - 1) / threadsPerBlock);


__global__ void dot(float *a, float *b, float *c)
{
__shared__ float cache[threadsPerBlock];
int tid = threadIdx.x + blockIdx.x*blockDim.x;
int cacheIndex = threadIdx.x;


float temp = 0;
while (tid<N)
{
temp += a[tid] * b[tid];
tid += blockDim.x*gridDim.x;


}
cache[cacheIndex] = temp;
__syncthreads();


int i = blockDim.x / 2;
while (i!=0)
{
if (cacheIndex < i)
cache[cacheIndex] += cache[cacheIndex + i];
__syncthreads();
i /= 2;
}
if (cacheIndex == 0)
c[blockIdx.x] = cache[0];
}
int main(void)
{
float *a, *b, c, *partial_c;
float *dev_a, *dev_b, *dev_partial_c;


//在CPU上分配内存
a = (float*)malloc(N*sizeof(float));
b = (float*)malloc(N*sizeof(float));
partial_c = (float*)malloc(blocksperGrid*sizeof(float));


//在GPU上分配内存
cudaMalloc((void**)&dev_a, N*sizeof(float));
cudaMalloc((void**)&dev_b, N*sizeof(float));
cudaMalloc((void**)&dev_partial_c, blocksperGrid*sizeof(float));


for (int i = 0; i < N; i++)
{
a[i] = i;
b[i] = i * 2;
}
cudaMemcpy(dev_a, a, N*sizeof(float), cudaMemcpyHostToDevice);
cudaMemcpy(dev_b, b, N*sizeof(float), cudaMemcpyHostToDevice);
dot <<<blocksperGrid, threadsPerBlock>>>(dev_a, dev_b, dev_partial_c);
cudaMemcpy(partial_c, dev_partial_c, blocksperGrid*sizeof(float), cudaMemcpyDeviceToHost);
c = 0;
for (int i = 0; i < blocksperGrid; i++)
{
c += partial_c[i];
}
cout << c << endl;
cudaFree(dev_a);
cudaFree(dev_b);
cudaFree(dev_partial_c);


free(a);
free(b);
free(partial_c);








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