RE: [Dev-C++] speed test

[Ioannis V. <no...@ho...>]

> -----Original Message-----
> From: dev...@li... 
> [mailto:dev...@li...] On Behalf 
> Of mo...@ju...
> Sent: Friday, August 16, 2002 8:02 AM
> To: dev...@li...
> Subject: [Dev-C++] speed test
> 
> 
> Running the program below in Dev-C++, Version 4, took between 
> 209 and 235
> seconds on my system.  I don't know why the running times 
> vary, but even
> taking the fastest time of 209 seconds, it compares unfavorably with a
> similar program compiled (36 seconds) or interpreted  (55 seconds) in
> QBasic 4 .  


Did you printed the result after every x++ inside the for loop in QB?



> 
> Does Dev-C++ really produce such leisurely code?  Or can the 
> program be
> speeded up?


Of course it can. Printing in console is slow (the time cost of a
function call, etc).



>  
> Allan
> 
> // This program prints (1) integers 1 to 1,000,000
> //                                (2) starting & ending times
> //======================================================
> #include <stdio.h>
> #include <stdlib.h> 
> #include <time.h>
> 
> int main(int argc, char *argv[])

Theese arguments are not needed.


> {
> struct tm *ptr;
> time_t loc_time;
> long int x;
> 
> loc_time  = time(NULL);


No accurate results with this method.



> ptr = localtime(&loc_time);
> 
> for (x = 1;x <= 1000000;x++)
>         printf("%d ",x);


Here you have 100000 function calls for printing in the console.


> 
> printf("\nStarting time is ");
> printf(asctime(ptr));
> 
> loc_time =  time(NULL);
> ptr = localtime(&loc_time);
> printf("\nEnding time is ");
> printf(asctime(ptr), "\n");
> 
> system ("PAUSE");
> 
> return 0;
> }


A better program:


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

int main()
{
 clock_t t1, t2;

 long int x;

 t1=clock();

 for (x = 1; x <= 1000000;x++)
     ;
     
 printf("%ld\n", x);

 t2=clock();

 printf("\n\nProcessor time: %lu", (unsigned long)t2-t1);
 printf("\nIn seconds: %f\n\n", (double)(t2-t1)/CLOCKS_PER_SEC);

 system ("PAUSE");

 return 0;
}



The above prints the final value of x only.



Using MINGW GCC 3.1 with optimizations:


gcc temp.c -o temp -ansi -pedantic-errors -Wall
-fexpensive-optimizations -O3 -ffloat-store -mcpu=pentiumpro


C:\c>temp
1000001


Processor time: 0
In seconds: 0.000000

Press any key to continue . . .



Here obviously the compiler performed an optimisation with which he saw
the final result of the loop and avoided the loop completely.


Running the GCC 3.1 without the optimisation switches:


C:\c>gcc temp.c -o temp -ansi -pedantic-errors -Wall

C:\c>temp
1000001


Processor time: 10
In seconds: 0.010000

Press any key to continue . . .



Here it performed the loop and it took it 10 msec (something similar
will happen with Dev-C++ eith optimisations off).


In summary, your time cost was imposed due to 1000000 function calls to
printf().



Ioannis

* Ioannis Vranos
* Programming pages: http://www.noicys.cjb.net
* Alternative URL: http://run.to/noicys