difference w.r.t time

difference w.r.t time

[Ankit Jain]

i want to know why these programs dont give the same
output

i am trying to do benchmarking. 1st program is using
malloc and another array

i am not taking the allocations into account. i am
just looking for for loop

i dont understand why they show diff. time

thanks

ankit
******************************************
PROGRAM 1

#include<stdlib.h>
#include<stdio.h>
#include<sys/time.h>
#define NR 4096 
#define NC 4096 
#define N  NR*NC

int main()
{
   unsigned long i,j,k,d=2;
   double cont2=0,cont1=0,mean=0;
   struct timeval start,end; 
   double *a;//,*a1;
   a1=malloc(sizeof(double)*N);

   k=0;
   for (i = 0; i < NR; i++)
     {
       for (j = 0; j < NC; j++)
         {
          *(a+i+j) = k;
           mean = mean+*(a+i+j);
         }
     }
    mean = mean/( (float)NR*(float) NC);
	gettimeofday(&start,NULL);

/* here is the 2d contrast module*/

   for (i = 0; i<(NR-d); i++)
      {
       for (j = 0; j<(NC-d); j++)
         {
          cont2  = cont2
+(*(a+i+d+j)-*(a+i+j))*(*(a+i+d+j)-*(a+i+j))+
                       
+(*(a+i+j+d)-*(a+i+j))*(*(a+i+j+d)-*(a+i+j));
         }
      } 
       cont2 = cont2/(mean*mean);
       printf("contrast :(2D) %f\n", cont2);

	gettimeofday(&end,NULL);
	printf("Time :%ld ",(-start.tv_sec + end.tv_sec));

return 0;
}


*********************************************
Program 2

#include<stdlib.h>
#include<stdio.h>

#define NR 4096
#define NC 4096
#define N  (NR*NC)

int main()
{
   unsigned long i,j,k,d=2;
   double cont2=0,cont1=0,mean=0;
   double a[NR][NC]={},a1[N]={};
  struct timeval start,end;
   k=0;
   for (i = 0; i < NR; i++)
     {
       for (j = 0; j < NC; j++)
        {
          a[i][j] = k;
          mean = mean+a[i][j];
	}
     }
    mean = mean/( (float)NR*(float) NC);
   gettimeofday(&start,NULL);
// here is the 2d contrast module

    for (i = 0; i<(NR-d); i++)
      {
       for (j = 0; j<(NC-d); j++)
         {
          cont2  = cont2
+(a[i+d][j]-a[i][j])*(a[i+d][j]-a[i][j])+
                       
+(a[i][j+d]-a[i][j])*(a[i][j+d]-a[i][j]);
         }
      } 
       cont2 = cont2/(mean*mean);
       printf("contrast :(2D) %f\n", cont2);

gettimeofday(&end,NULL);
printf("Time :%ld",end.tv_sec - start.tv_sec);
return 0;
}


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