Re: Clang as default compiler November 4th

On Sat, Sep 15, 2012 at 7:30 AM, Tijl Coosemans <tijl_at_coosemans.org> wrote:

> On 15-09-2012 16:09, Roman Divacky wrote:
> > Is this correct?
> >
> > lev ~$ ./cos 1.23456789e20
> > 6.031937e-01
> > -9.629173e-02
> > 2.814722e-01
>
> Yes, that's what the libm call returns.
>
>



Linux z 3.5.3-1.fc17.x86_64 #1 SMP Wed Aug 29 18:46:34 UTC 2012 x86_64
x86_64 x86_64 GNU/Linux

clang version 3.0 (tags/RELEASE_30/final)
Target: x86_64-redhat-linux-gnu
Thread model: posix


Output of the initial program is the following :

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

int
main( int argc, char **argv ) {
        double d = strtod( argv[ 1 ], NULL );

        printf( " cos : %e\n", ( double ) cos( d ));
        printf( "cosf : %e\n", ( double ) cosf( d ));
        printf( "cosl : %e\n", ( double ) cosl( d ));
        return( 0 );
}


cos : 2.814722e-01
cosf : -9.629173e-02
cosl : 7.738403e-01


.......................................................


Output of the following program is different :


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

int
main( int argc, char **argv ) {
        double d ;
        double two_pi ;
        double f ;
        double v ;

    two_pi = 2 * 3.14159265358979323846 ;
        d = strtod( argv[ 1 ], NULL );

    f = floor ( d / two_pi ) ;
        v = d - f * two_pi ;

        printf( "  given : %e\n", ( double ) d );
        printf( "  multiplier : %e\n", ( double ) f );
        printf( "reduced : %e\n", ( double ) v );


        printf( " cos ( %e ) : %e\n", d , ( double ) cos( d ));
        printf( "cosf ( %e ) : %e\n", d , ( double ) cosf( d ));
        printf( "cosl ( %e ) : %e\n", d , ( double ) cosl( d ));


        printf( " cos ( %e ) : %e\n", v , ( double ) cos( v ));
        printf( "cosf ( %e ) : %e\n", v , ( double ) cosf( v ));
        printf( "cosl ( %e ) : %e\n", v , ( double ) cosl( v ));


    return( 0 );
}


  given : 1.234568e+20
  multiplier : 1.964876e+19
reduced : 1.638400e+04


 cos ( 1.234568e+20 ) : 2.814722e-01
cosf ( 1.234568e+20 ) : -9.629173e-02
cosl ( 1.234568e+20 ) : 7.738403e-01

 cos ( 1.638400e+04 ) : -8.285342e-01
cosf ( 1.638400e+04 ) : -8.285342e-01
cosl ( 1.638400e+04 ) : -8.285342e-01

.......................................................

Reduction of argument once more did NOT change results :



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

int
main( int argc, char **argv ) {
        double d ;
        double two_pi ;
        double f ;
        double v ;
        double g ;
        double w ;


    two_pi = 2 * 3.14159265358979323846 ;
        d = strtod( argv[ 1 ], NULL );


        printf( "     given : %e\n", ( double ) d );


        printf( " cos ( %e ) : %e\n", d , ( double ) cos( d ));
        printf( "cosf ( %e ) : %e\n", d , ( double ) cosf( d ));
        printf( "cosl ( %e ) : %e\n", d , ( double ) cosl( d ));


    f = floor ( d / two_pi ) ;
        v = d - f * two_pi ;

        printf( "multiplier : %e\n", ( double ) f );
        printf( "   reduced : %e\n", ( double ) v );


        printf( " cos ( %e ) : %e\n", v , ( double ) cos( v ));
        printf( "cosf ( %e ) : %e\n", v , ( double ) cosf( v ));
        printf( "cosl ( %e ) : %e\n", v , ( double ) cosl( v ));


    g = floor ( v / two_pi ) ;
        w = v - g * two_pi ;

        printf( "multiplier : %e\n", ( double ) g );
        printf( "   reduced : %e\n", ( double ) w );


        printf( " cos ( %e ) : %e\n", w , ( double ) cos( w ));
        printf( "cosf ( %e ) : %e\n", w , ( double ) cosf( w ));
        printf( "cosl ( %e ) : %e\n", w , ( double ) cosl( w ));


    return( 0 );
}



     given : 1.234568e+20
 cos ( 1.234568e+20 ) : 2.814722e-01
cosf ( 1.234568e+20 ) : -9.629173e-02
cosl ( 1.234568e+20 ) : 7.738403e-01

multiplier : 1.964876e+19
   reduced : 1.638400e+04
 cos ( 1.638400e+04 ) : -8.285342e-01
cosf ( 1.638400e+04 ) : -8.285342e-01
cosl ( 1.638400e+04 ) : -8.285342e-01

multiplier : 2.607000e+03
   reduced : 3.735904e+00
 cos ( 3.735904e+00 ) : -8.285342e-01
cosf ( 3.735904e+00 ) : -8.285342e-01
cosl ( 3.735904e+00 ) : -8.285342e-01


.......................................................



Thank you very much .

Mehmet Erol Sanliturk