degree_count.cu

#include <stdio.h>
#include <cuda.h>
#define check( a ) \
{\
    if ( (a) != 0 ) {\
        printf("ERROR in %s : %d\n", __FILE__ , __LINE__ );\
        exit(0);\
    }\
}

__global__ void calculate_degree(int m, int* dev_edges, int* dev_nodes){
    int from = blockDim.x * blockIdx.x + threadIdx.x;
    int step = gridDim.x * blockDim.x;
    for (int i = from; i < m; i += step) {
        int prev = dev_edges[2 * i];
        int next = dev_edges[2 * i + 1];
        atomicAdd(dev_nodes + prev, 1);
        atomicAdd(dev_nodes + next, 1);
    }
}
int main(){
  int n = 4;
  int m = 5;
  int edges[] = {0, 1, 1, 2, 2, 3, 3, 1, 2, 0};
  int nodes[] = {0, 0, 0, 0};
  int* dev_edges;
  int* dev_nodes;
  check(cudaMalloc(&dev_edges, 2 * m * sizeof(int)));
  check(cudaMalloc(&dev_nodes, n * sizeof(int)));
  check(cudaMemcpy(dev_edges, edges, 2 * m * sizeof(int), cudaMemcpyHostToDevice));
  check(cudaMemcpy(dev_nodes, nodes, n * sizeof(int), cudaMemcpyHostToDevice));
  calculate_degree<<<1, 256>>>(m, dev_edges, dev_nodes);  
  check(cudaMemcpy(nodes, dev_nodes, n * sizeof(int), cudaMemcpyDeviceToHost));
  for (int i = 0; i < 4; i++) {
     printf("Node %d: degree %d\n", i, nodes[i]);
  }

}