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Message-ID: <20190227201608.GH21289@port70.net>
Date: Wed, 27 Feb 2019 21:16:09 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: FE Exception triggered by comparison
* Alexander Monakov <amonakov@...ras.ru> [2019-02-27 22:48:02 +0300]:
> On Wed, 27 Feb 2019, Rich Felker wrote:
> > Ideally the compiler would be able to recognize portable (within IEEE)
> > patterns for floating point representation examination and optimize
> > them if there's a more efficient way to be able to do it for a
> > particular machine.
>
> There's a difference for sNaN operands: the bit-test version obviously
> is not going to raise "invalid", while comparing the fpu register with
> itself will. So I'm afraid the compiler wouldn't do that for x86 (but
> could for targets where an suitable instruction is available).
using -fsignaling-nan is extremely rare, by default the transformation
is valid (but maybe tricky anyway).
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