fractal-mpi.cpp

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   *  Author: Martin Burtscher <burtscher@txstate.edu>                         
*/

#include <stdlib.h>
#include <stdio.h>
#include <malloc.h>
#include <assert.h>
#include <sys/time.h>
#include <mpi.h>

#include "writeBMP.hpp"

#define xMin 0.74395
#define xMax 0.74973
#define yMin 0.11321
#define yMax 0.11899

int main(int argc, char *argv[])
{
  int row, col, depth, width, maxdepth, local_width;
  double cx, cy, dx, dy, x, y, x2, y2;
  unsigned char *cnt;
  unsigned char *local_cnt;
  struct timeval start, end;
  int comm_sz, my_rank;
  double local_start, local_finish, local_elapsed, elapsed;
  int my_start, my_end;
  
  /* Initialize MPI Library and get # of processes/ assigned ranks */
  MPI_Init(NULL, NULL);
  MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);
  MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

  if (my_rank ==0){
    printf("Fractal v1.2\n");
    printf("There are %d processes available\n", comm_sz);}

  /* check command line */
  if (argc != 3) 
    {fprintf(stderr, "usage: %s edge_length max_depth\n", argv[0]); exit(-1);}
  width = atoi(argv[1]);
  if (width < 10) 
    {fprintf(stderr, "edge_length must be at least 10\n"); exit(-1);}
  maxdepth = atoi(argv[2]);
  if (maxdepth < 10) 
    {fprintf(stderr, "max_depth must be at least 10\n"); exit(-1);}

  /* width is an integer multiple of the # of processes */
  assert(width % comm_sz ==0);

  /* array for local computations*/
  local_cnt = (unsigned char *)malloc((width / comm_sz) * width * 
    sizeof(unsigned char));
  
  if (NULL == local_cnt) {
    fprintf(stderr, "could not allocate memory\n");
    exit(-1);
  }

  if(my_rank ==0){
    printf("computing %d by %d fractal with a maximum depth of %d\n", width, 
      width, maxdepth);

    /* allocate array for entire fractal */
    cnt = (unsigned char *)malloc(width * width * sizeof(unsigned char));
    if (cnt == NULL) 
      {fprintf(stderr, "could not allocate memory\n"); exit(-1);}
  }
  
  /* start time */
  MPI_Barrier(MPI_COMM_WORLD);
  if (my_rank ==0)
    gettimeofday(&start, NULL);

  local_width = width / comm_sz;

  /* compute fractal */
  dx = (xMax - xMin) / width;
  dy = (yMax - yMin) / width;
  my_start = my_rank * width / comm_sz;
  for (row = 0; row  < local_width; row++) {
    cy = yMin + (my_start + row) * dy;
    cx = xMin;
    local_width = width / comm_sz;
    for (col = 0; col < width; col++) { 
      cx = xMin + col *dy;
      x = -cx;
      y = -cy;
      depth = maxdepth;
      do {
        x2 = x * x;
        y2 = y * y;
        y = 2 * x * y - cy;
        x = x2 - y2 - cx;
        depth--;
      } while ((depth > 0) && ((x2 + y2) <= 5.0));
      local_cnt[row * width + col] = depth & 255; 
    }
  }

  MPI_Gather(local_cnt, (local_width * width), MPI_UNSIGNED_CHAR, cnt, 
    (local_width * width), MPI_UNSIGNED_CHAR, 0, MPI_COMM_WORLD); 

  if(my_rank ==0){
    gettimeofday(&end, NULL); /* end time */

    /* print time */
    printf("compute time: %.4f s\n", end.tv_sec + end.tv_usec / 
      1000000.0 - start.tv_sec - start.tv_usec / 1000000.0);

    /* verify result by writing it to a file */
    if (width <= 1024)
      WriteBMP(width, width, cnt, "fractal.bmp");

    if (cnt != NULL){
      free(cnt);
      cnt = NULL;
    }
  }
  
  if (local_cnt != NULL){
    free(local_cnt);
    local_cnt = NULL;
  }

  MPI_Finalize();
  return 0;
}