Re: powerpc(32) point/polygon regression failures on Debian Jessie

From: Christoph Berg <christoph(dot)berg(at)credativ(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: powerpc(32) point/polygon regression failures on Debian Jessie
Date: 2017-02-21 10:05:53
Message-ID: 20170221100553.6acj65iq374cgzc5@msg.credativ.de
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Re: To Tom Lane 2017-02-20 <20170220161556(dot)5ukosuj5o572b4rn(at)msg(dot)credativ(dot)de>
> I was compiling the program on jessie and on sid, and running the
> jessie binary on sid made it output the same as the sid binary, so the
> difference isn't in the binary, but in some system library.

Fwiw, the problem will be fixed in Jessie's glibc by backporting this update:

2015-02-12 Joseph Myers <joseph(at)codesourcery(dot)com>

[BZ #17964]
* sysdeps/powerpc/fpu/e_sqrt.c (__slow_ieee754_sqrt): Use
__builtin_fma instead of relying on contraction of a * b + c.

https://anonscm.debian.org/cgit/pkg-glibc/glibc.git/commit/?h=jessie&id=b26c084f6eba0057b1cd93e0caf424a1d06bd97e

(Upstream it's probably one of these, didn't dig deeper:
https://sourceware.org/git/?p=glibc.git&a=search&h=HEAD&st=commit&s=__builtin_fma)

Thanks for the input,
Christoph
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