Date: Tue, 18 Sep 2012 09:20:05 -0700 From: Mehmet Erol Sanliturk <m.e.sanliturk@gmail.com> To: Tijl Coosemans <tijl@coosemans.org> Cc: toolchain@freebsd.org, current@freebsd.org Subject: Re: Clang as default compiler November 4th Message-ID: <CAOgwaMtxXtFLtxsk=vqSF6_5P5EZ-gEYp3ru0epTGSMTbEpZ1Q@mail.gmail.com> In-Reply-To: <505883E3.3050103@coosemans.org> References: <504F5101.8090906@FreeBSD.org> <505101C3.70203@freebsd.org> <20120913020833.GA8255@troutmask.apl.washington.edu> <1347550332.1110.108.camel@revolution.hippie.lan> <20120913161024.GA13846@troutmask.apl.washington.edu> <20120914202319.GB5244@lor.one-eyed-alien.net> <20120915001808.GA70215@troutmask.apl.washington.edu> <20120915010600.GA70426@troutmask.apl.washington.edu> <20120915124809.GA10939@freebsd.org> <50548736.9030203@coosemans.org> <20120915140933.GA17801@freebsd.org> <505490FB.2000807@coosemans.org> <CAOgwaMvtSXoGCYnX%2BA3DzMffXo6mhHk=EWWO=1k7SWuAiH21xg@mail.gmail.com> <505883E3.3050103@coosemans.org>
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On Tue, Sep 18, 2012 at 7:23 AM, Tijl Coosemans <tijl@coosemans.org> wrote:
> On 15-09-2012 17:39, Mehmet Erol Sanliturk wrote:
> > On Sat, Sep 15, 2012 at 7:30 AM, Tijl Coosemans <tijl@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
>
> This is probably because SSE instructions are used on amd64.
>
> > Output of the following program is different :
>
> The reason is that...
>
> > #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 ;
>
> ...this is a poor way to compute a remainder. Try to use fmod() or
> remainder() instead.
>
My C knowledge is NOT very well . Thanks .
>
> > 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
>
>
My intention was to check whether there is a difference between Clang
compiled programs in different operating systems .
The GCC output is as follows :
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
cc (GCC) 4.7.0 20120507 (Red Hat 4.7.0-5)
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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
This shows that GCC is NOT better than Clang .
Thank you very much .
Mehmet Erol Sanliturk
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