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Date: Wed, 06 Nov 2002 13:36:00 -0000
From: Jan Hubicka <jh@suse.cz>
To: Gabriel Dos Reis <gdr@integrable-solutions.net>
Cc: Jan Hubicka <jh@suse.cz>, Richard Henderson <rth@redhat.com>,
	gcc-patches@gcc.gnu.org, aj@suse.de
Subject: Re: Simplify floating point conversions II
Message-ID: <20021106213652.GF1316@atrey.karlin.mff.cuni.cz>
References: <20021105171400.GX14655@kam.mff.cuni.cz> <20021105173800.GD20534@redhat.com> <20021106092310.GE22059@kam.mff.cuni.cz> <20021106175441.GZ22059@kam.mff.cuni.cz> <20021106180930.GA22066@redhat.com> <20021106211059.GB1316@atrey.karlin.mff.cuni.cz> <m365va2xfl.fsf@soliton.integrable-solutions.net>
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> Jan Hubicka <jh@suse.cz> writes:
> 
> | > On Wed, Nov 06, 2002 at 06:54:41PM +0100, Jan Hubicka wrote:
> | > > +      For fast math it would be safe probably to convert (float)sqrt(x)
> | > > +      into sqrt((float)x), but in strict mode the argument can overflow.  */
> | > 
> | > I don't believe this to be true.
> | 
> | What you don't believe?
> 
> Likew RTH, I, skeptical that your assertion is right.
> 
> | That in ffast-math we can do the transformation?
> 
> Do we really need to do that transformation?  That is is there any
> real evidence that it brings any real benefit?
> I would be reluctant to include it even in -funsafe-math.
I am not implementing that transformation, so I am not sure.
Doing the cases I do right now and I believe to be safe brings quite
considerable amount of matches in standard C 3d graphics code that does
a lot of float and some casts to double coming from implicit C stuff.

Honza
> 
> -- Gaby