# include  <stdio.h> 

int main ( );
void loadArrays ( int n, float *a_cpu, float *b_cpu );
__global__ void add_vectors ( float *a_gpu, float *b_gpu, float *c_gpu );

int main ( ) 
{
  float *a_cpu;
  float *a_gpu;
  float *b_cpu;
  float *b_gpu;
  float *c_cpu;
  float *c_gpu;
  int i;
  int memsize;
  int n; 

  printf ( "\n" );
  printf ( "VECADD:\n" );
  printf ( "  CUDA/C version.\n" );
  printf ( "  Transfer vectors A and B to GPU, compute sum C.\n" );
//
//  Set size of vectors;
//
  n = 10;
//
//  Allocate A and B on the CPU.
//
  memsize = n * sizeof ( float );
  a_cpu = ( float * ) malloc ( memsize );
  b_cpu = ( float * ) malloc ( memsize );
//
// Load A and B with random floats.
//
  loadArrays ( n, a_cpu, b_cpu );
//
// Allocate memory on the GPU.
//
  cudaMalloc ( ( void** ) &a_gpu, memsize ); 
  cudaMalloc ( ( void** ) &b_gpu, memsize ); 
  cudaMalloc ( ( void** ) &c_gpu, memsize ); 
//
// Copy a_gpu <= a_cpu, from host to device.
//
  cudaMemcpy ( a_gpu, a_cpu, memsize, cudaMemcpyHostToDevice );
// 
// Copy b_gpu <= b_cpu, from host to device.
//
  cudaMemcpy ( b_gpu, b_cpu, memsize, cudaMemcpyHostToDevice );
//
// Launch the kernel on the device.
// 
  add_vectors <<< 1, n >>> ( a_gpu, b_gpu, c_gpu ); 
//
// Copy c_cpu <= c_gpu from device to host.
//
  c_cpu = ( float * ) malloc ( memsize );
  cudaMemcpy ( c_cpu, c_gpu, memsize, cudaMemcpyDeviceToHost ); 
//
// Print the results.
//
  printf ( "\n" );
  printf ( "   i     A[i]      B[i]     C[i]=A[i]+B[i]\n" );
  printf ( "\n" );
  for ( i = 0; i < n && i < 10; i++ ) 
  {
    printf ( "  %2d  %8.2f  %8.2f  %8.2f\n", i, a_cpu[i], b_cpu[i], c_cpu[i] );
  }
//
//  Free CPU memory.
//
  free ( a_cpu );
  free ( b_cpu );
  free ( c_cpu );
// 
// Free GPU memory.
//
  cudaFree ( a_gpu ); 
  cudaFree ( b_gpu ); 
  cudaFree ( c_gpu ); 
//
//  Terminate.
//
  printf ( "\n" );
  printf ( "VECADD:\n" );
  printf ( "  Normal end of execution.\n" );

  return 0;
}

void loadArrays ( int n, float *a_cpu, float *b_cpu )
{
  int i;

  srand ( 1 );

  for ( i = 0; i < n; i++ )
  {
    a_cpu[i] = ( float ) rand ( ) / ( ( float ) RAND_MAX / 100 );
    b_cpu[i] = ( float ) rand ( ) / ( ( float ) RAND_MAX / 100 );
  }

  return;
}
__global__ void add_vectors ( float *a_gpu, float *b_gpu, float *c_gpu ) 
{
//
// threadIdx.x is a built-in variable provided by CUDA at runtime.
//
  int i = threadIdx.x; 

  c_gpu[i] = a_gpu[i] + b_gpu[i]; 

  return;
}