GNU bug report logs - #11913
Unusual Emacs 24.1 arithmetic error (abs) on i386 machine

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Message #71 received at 11913 <at> debbugs.gnu.org (full text, mbox):

From: Rob Browning <rlb <at> defaultvalue.org>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 11913 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#11913: Unusual Emacs 24.1 arithmetic error (abs) on i386
	machine
Date: Mon, 16 Jul 2012 21:33:58 -0500

Rob Browning <rlb <at> defaultvalue.org> writes:

> Glenn Morris <rgm <at> gnu.org> writes:
>
>> But why does (abs 8.0) return an arithmetic error at all...?
>
> OK, at the moment, I believe the short answer is because fabs() is
> changing errno which triggers the default clause in IN_FLOAT() here:
>
>     default: arith_error (float_error_fn_name, float_error_arg);
>
> I've been told that this should be considered an Emacs bug because the
> effect of fabs() on errno is strictly undefined, and so fabs() is within
> its rights to do whatever it wants to the value.

For now, I'm going to deploy a patch in the Debian package that just
adds a DEB_IN_FLOAT_NOERRNO() that omits the errno checking, and then
uses that macro for the fabs() call.

Doing something with a similar result would probably be advisable.

Thanks for the help.
-- 
Rob Browning
rlb @defaultvalue.org and @debian.org
GPG as of 2002-11-03 14DD 432F AE39 534D B592 F9A0 25C8 D377 8C7E 73A4

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