From: Corinna Vinschen <vinschen@redhat.com>
To: newlib@sourceware.org
Subject: Re: [PATCH] Don't call double rint from float powf.
Date: Tue, 12 Dec 2017 12:49:00 -0000 [thread overview]
Message-ID: <20171212124855.GA9113@calimero.vinschen.de> (raw)
In-Reply-To: <1bd39401-e1b2-5be6-4418-9e6a809964da@LGSInnovations.com>
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On Dec 11 19:37, Craig Howland wrote:
> On 12/11/2017 07:08 PM, Jim Wilson wrote:
> > This is the first patch of two to fix problems with the powf code. I haven't
> > written the other patch yet.
> >
> > For targets that have only single float support, such as RISC-V rv32imafc, a
> > program using powf ends up pulling in soft-float adddf3 and subdf3 routines.
> > These come from the double rint call, which should be float rintf instead.
> > This makes a significant difference in the size of the resulting program.
> >
> > I tested this with a simple testcase, with an rint function that calls abort
> > to verify that I'm testing the right code path. Compiling with
> > "gcc -fno-builtin" I get for the patched and unpatched newlib
> >
> > gamma02:2195$ ls -lt a.out*
> > -rwxrwxr-x 1 jimw jimw 47012 Dec 11 15:01 a.out
> > -rwxrwxr-x 1 jimw jimw 75680 Dec 11 14:46 a.out.unpatched
> > gamma02:2196$
> >
> > So the result with the patch is about 60% of the size without the patch. The
> > test program gives the correct result with the patch. I also ran the newlib
> > make check, which passed with no regression, but I see it doesn't do much
> > useful.
> >
> > newlib/
> > * libm/math/wf_pow.c (powf): Call rintf instead of rint.
> > ---
> > newlib/libm/math/wf_pow.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/newlib/libm/math/wf_pow.c b/newlib/libm/math/wf_pow.c
> > index be453558b..4ca0dc79d 100644
> > --- a/newlib/libm/math/wf_pow.c
> > +++ b/newlib/libm/math/wf_pow.c
> > @@ -127,11 +127,11 @@
> > if (_LIB_VERSION == _SVID_) {
> > exc.retval = HUGE;
> > y *= 0.5;
> > - if(x<0.0&&rint(y)!=y) exc.retval = -HUGE;
> > + if(x<0.0&&rintf(y)!=y) exc.retval = -HUGE;
> > } else {
> > exc.retval = HUGE_VAL;
> > y *= 0.5;
> > - if(x<0.0&&rint(y)!=y) exc.retval = -HUGE_VAL;
> > + if(x<0.0&&rintf(y)!=y) exc.retval = -HUGE_VAL;
> > }
> > if (_LIB_VERSION == _POSIX_)
> > errno = ERANGE;
> To be most rigorous, "0.0" on the same lines as the rintf() should be "0.0F"
> (as otherwise the comparison strictly should be done in double). (Not
> addressing the exact change you are making, but is the same class of fix and
> are on the same line of source code.)
Also, HUGE_VAL is double, so it should better be replaced with HUGE_VALF.
Thanks,
Corinna
--
Corinna Vinschen
Cygwin Maintainer
Red Hat
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next prev parent reply other threads:[~2017-12-12 12:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-12 0:14 Jim Wilson
2017-12-12 3:45 ` Craig Howland
2017-12-12 12:49 ` Corinna Vinschen [this message]
2017-12-12 18:14 ` Jim Wilson
2017-12-12 18:05 ` Jim Wilson
2017-12-12 19:00 ` Craig Howland
2017-12-12 19:39 ` [PATCH v2] " Jim Wilson
2017-12-13 10:35 ` Corinna Vinschen
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