par_lab4.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/timeb.h>

#define N 1000

int main() {
  double *a, *b, *c;
  int i, j, k;
  double mflop, sum;
  struct timeb ts, te;
  a = (double *)malloc(N*N*sizeof(double));
  if (a==NULL) { exit(1); }
  b = (double *)malloc(N*N*sizeof(double));
  if (b == NULL){free(a); exit(1);}
  c = (double *)malloc(N*N*sizeof(double));
  if (c == NULL){free(a); free(b); exit(1);}
  //b = &a[N*N];


  for (i=0;i<N*N;i++) {
    a[i] = 2.0;
    b[i] = 3.0;
    c[i] = b[i];
  }

  double b_cell = 3.0*2.0*N;
  ftime(&ts);
  //i*N + j
  //i + j*Ν
  // loop unrolling
  for (i=0;i<N;i+=4) {
    for (j=0;j<N;j++) {
      c[i*N + j] = b[j*N + i];
      c[i*(N + 1) + j ] = b[j*N + i + 1];
      c[i*(N + 2) + j ] = b[j*N + i + 2];
      c[i*(N + 3) + j ] = b[j*N + i + 3];
    }
  }

  // c is now b^T

  for(i = 0; i<N; i++){ // grammes tou a
    for(j = 0; j<N; j++){ // grammes toy c
      sum = 0.0; // b[i,j]
      for(k = 0; k<N; k++){
        sum += a[i*N + k]*c[j*N + k];
      }
      b[i*N + j] = sum;
    }
  }

  ftime(&te);

  for (i=0;i<N;i++) {
    for (j = 0; j<0; j++){
      if(b[i*N+j] != b_cell ) {
        printf("error\n");
        break;
      }
    }
  }
  free(a);
  free(b);
  free(c);
  int diff = (int) (1000.0 * (te.time - ts.time)
          + (te.millitm - ts.millitm));
  printf("Time in milliseconds:%d\n", diff);
  return 0;
}