Re: difference w.r.t time

[Muthukumar Ratty <muthu at iqmail dot net>]

Hi,
Again.... this is not relevant to gcc-help. You will get the same result
with any sane compiler. Please *on topic* questions only.

For your question, look at the assembly output.

thanks,
Muthu.



On Mon, 27 Sep 2004, Ankit Jain wrote:

> 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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