GNU bug report logs - #5754
Bytecomp Arithmetic test failed

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Message #54 received at 5754 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Chong Yidong <cyd <at> stupidchicken.com>
Cc: Juri Linkov <juri <at> jurta.org>, 5754 <at> debbugs.gnu.org
Subject: Re: bug#5754: Bytecomp Arithmetic test failed
Date: Sun, 04 Apr 2010 10:05:03 +0200

Chong Yidong <cyd <at> stupidchicken.com> writes:

> The key is that if I compile Emacs with CFLAGS="-g", then
>
> (funcall
>  (byte-compile
>   (list 'lambda nil
> 	(quote (let ((a (expt 2 -1074)) (b 0.125)) (* a 8 b))))))
>
> returns 0.0.  If I compile Emacs with CFLAGS="-g -O2", then it returns
> 5e-324.
>
> It looks like this may be a compiler bug.

It's most likely the effect of excess precision, due to floating point
values being held in registers instead of reloaded from memory.  Try
-ffloat-store.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
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