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Date: Thu, 11 Sep 2014 16:11:23 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] Make musl math depend less on libgcc builtins
* Sergey Dmitrouk <sdmitrouk@...esssoftek.com> [2014-09-11 16:22:53 +0300]:
> Note that I'm performing tests in QEMU. vsqrt.f64 instruction returns
> NAN for NAN input and doesn't raise any exceptions ($fpscr register is
> unchanged). However I get INVALID exception after printing result with
> musl implementation of printf(), glibc doesn't raise any exceptions in
> printf(), but I'm not sure whether it's important, probably not.
nan printf should not raise invalid exceptino in musl either
musl checks for nan by if(y!=y) and my guess is that this is
incorrectly done by a signaling comparision
i checked on x86_64 and both clang and gcc get comparisions
wrong in the other direction: they use quite comparisions
when signaling is needed, eg
http://goo.gl/GsdpZA
(on a correct implementation ==, != are quiet, but <,>,<=,>=
raise invalid if any of the operands are nan, on x86_64 the
quiet instruction is ucomis* and the signaling one is comis*
and both gcc-4.9 and clang-3.4 seem to use ucomis* for all
relational operations, may be there is some compiler flag to
make them behave..)
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