/*  ----------------------- *\
    Vector Addition example
\*  ----------------------- */

#include <stdio.h>
#include <cuda_runtime.h>

/* CUDA kernel */
__global__ void vectorAdd( const float *A, 
			   const float *B, 
			   float *C, 
			   int numElements) {

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

  if (i < numElements) {
    C[i] = A[i] + B[i];
  }
}

/* ----- main ----- */
int main(void) {

  // Error code to check return values for CUDA calls
  cudaError_t err = cudaSuccess;

  // Print the vector length to be used, and compute its size
  int numElements = 5000000;
  size_t size = numElements * sizeof(float);
  printf("[Vector addition of %d elements]\n", numElements);

  // Allocate the host input and output vectors 
  float *h_A = (float *)malloc(size);
  float *h_B = (float *)malloc(size);
  float *h_C = (float *)malloc(size);

  // Verify that allocations succeeded
  if (h_A == NULL || h_B == NULL || h_C == NULL) {
    fprintf(stderr, "Failed to allocate host vectors!\n");
    exit(EXIT_FAILURE);
  }

  // Initialize the host input vectors
  for (int i = 0; i < numElements; ++i){
    h_A[i] = rand()/(float)RAND_MAX;
    h_B[i] = rand()/(float)RAND_MAX;
  }

  // Allocate the device vectors
  float *d_A = NULL;
  err = cudaMalloc((void **)&d_A, size);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to allocate device vector A (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  float *d_B = NULL;
  err = cudaMalloc((void **)&d_B, size);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to allocate device vector B (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  float *d_C = NULL;
  err = cudaMalloc((void **)&d_C, size);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to allocate device vector C (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  // Copy the host input vectors A and B in host memory to the device input vectors in device memory
  printf("Copy input data from the host memory to the CUDA device\n");
  err = cudaMemcpy(d_A, h_A, size, cudaMemcpyHostToDevice);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to copy vector A from host to device (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }
  err = cudaMemcpy(d_B, h_B, size, cudaMemcpyHostToDevice);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to copy vector B from host to device (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  // Launch the Vector Add CUDA Kernel
  int threadsPerBlock = 256;
  int blocksPerGrid =(numElements + threadsPerBlock - 1) / threadsPerBlock;
  printf("CUDA kernel launch with %d blocks of %d threads\n", blocksPerGrid, threadsPerBlock);
  vectorAdd<<<blocksPerGrid, threadsPerBlock>>>(d_A, d_B, d_C, numElements);
  err = cudaGetLastError();
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to launch vectorAdd kernel (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  // Copy the device result vector in device memory to the host result vector
  // in host memory.
  printf("Copy output data from the CUDA device to the host memory\n");
  err = cudaMemcpy(h_C, d_C, size, cudaMemcpyDeviceToHost);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to copy vector C from device to host (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  // Verify that the result vector is correct
  for (int i = 0; i < numElements; ++i){
    if (fabs(h_A[i] + h_B[i] - h_C[i]) > 1e-5){
      fprintf(stderr, "Result verification failed at element %d!\n", i);
      exit(EXIT_FAILURE);
    }
  }

  // Free device global memory
  err = cudaFree(d_A);

  if (err != cudaSuccess){
    fprintf(stderr, "Failed to free device vector A (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }
  err = cudaFree(d_B);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to free device vector B (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }
  err = cudaFree(d_C);
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to free device vector C (error code %s)!\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  // Free host memory
  free(h_A);
  free(h_B);
  free(h_C);

  // Reset the device and exit
  err = cudaDeviceReset();
  if (err != cudaSuccess){
    fprintf(stderr, "Failed to deinitialize the device! error=%s\n", cudaGetErrorString(err));
    exit(EXIT_FAILURE);
  }

  printf("Done\n");
  return 0;
}