Re: [PATCH] Make musl math depend less on libgcc builtins

[Szabolcs Nagy <nsz@port70.net>]

* Sergey Dmitrouk <sdmitrouk@accesssoftek.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..)