Date: Tue, 18 Sep 2012 16:23:31 +0200 From: Tijl Coosemans <tijl@coosemans.org> To: Mehmet Erol Sanliturk <m.e.sanliturk@gmail.com> Cc: toolchain@freebsd.org, current@freebsd.org Subject: Re: Clang as default compiler November 4th Message-ID: <505883E3.3050103@coosemans.org> In-Reply-To: <CAOgwaMvtSXoGCYnX%2BA3DzMffXo6mhHk=EWWO=1k7SWuAiH21xg@mail.gmail.com> 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>
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On 15-09-2012 17:39, Mehmet Erol Sanliturk wrote:
> On Sat, Sep 15, 2012 at 7:30 AM, Tijl Coosemans <tijl@coosemans.org> wr=
ote:=20
>> 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.=20
>=20
> 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
>=20
> clang version 3.0 (tags/RELEASE_30/final)
> Target: x86_64-redhat-linux-gnu
> Thread model: posix
>=20
>=20
> Output of the initial program is the following :
>=20
> #include <math.h>
> #include <stdio.h>
> #include <stdlib.h>
>=20
> int
> main( int argc, char **argv ) {
> double d =3D strtod( argv[ 1 ], NULL );
>=20
> printf( " cos : %e\n", ( double ) cos( d ));
> printf( "cosf : %e\n", ( double ) cosf( d ));
> printf( "cosl : %e\n", ( double ) cosl( d ));
> return( 0 );
> }
>=20
>=20
> 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>
>=20
> int
> main( int argc, char **argv ) {
> double d ;
> double two_pi ;
> double f ;
> double v ;
>=20
> two_pi =3D 2 * 3.14159265358979323846 ;
> d =3D strtod( argv[ 1 ], NULL );
>=20
> f =3D floor ( d / two_pi ) ;
> v =3D d - f * two_pi ;
=2E..this is a poor way to compute a remainder. Try to use fmod() or
remainder() instead.
> printf( " given : %e\n", ( double ) d );
> printf( " multiplier : %e\n", ( double ) f );
> printf( "reduced : %e\n", ( double ) v );
>=20
>=20
> 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 ));
>=20
>=20
> 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 ));
>=20
>=20
> return( 0 );
> }
>=20
>=20
> given : 1.234568e+20
> multiplier : 1.964876e+19
> reduced : 1.638400e+04
>=20
>=20
> cos ( 1.234568e+20 ) : 2.814722e-01
> cosf ( 1.234568e+20 ) : -9.629173e-02
> cosl ( 1.234568e+20 ) : 7.738403e-01
>=20
> cos ( 1.638400e+04 ) : -8.285342e-01
> cosf ( 1.638400e+04 ) : -8.285342e-01
> cosl ( 1.638400e+04 ) : -8.285342e-01
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