Help Needed for gcc on Linux x86_64

satyaakam goswami satyaakam@gmail.com
Thu May 18 10:30:00 GMT 2006


do you see these performance issue on any specific processors ?? as in
Intel or AMD...

Satya

On 5/18/06, Ashwani Bhat <ashwanib@cadence.com> wrote:
> On Linux 64 bit platform, gcc shows poor performance for pow() function
> when the first argument is very close to 1. To reproduce the issue, just
> create a simple c file case.c
>
> Contents of case.c
> ==================
> #include <stdio.h>
> #include <math.h>
>
> int main(){
>     double x;
>     int i;
>     for( i=1; i<10000; i++ ) {
>         x = pow( 1.0000000000000002, 1.5 );
>     }
>     printf( "x = %1.30f\n", x );
> }
>
> then compile it
> % gcc -lm -m64 case.c -o case
> % ./case
>
> Notes
> 1. gcc option -ffast-math does not help here
> 2. if compiled with "-m32" instead of "-m64", then the calculation is
> fast.
>
> Can you please help me here .. I have tried it with gcc -v3.2.3, 3.4.2,
> 4.1.0. But results are same.
>
>
> Thanks and regards,
> ------------------------------
> Ashwani Bhat
> /Grid Common Tools Team
> ashwanib@cadence.com
> ------------------------------------------
>



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