GNU bug report logs - #19025
24.4; precision error when adding two floats

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Package: emacs;

Reported by: "Kevin W. Currey" <kevalier68 <at> hotmail.com>

Date: Wed, 12 Nov 2014 01:25:02 UTC

Severity: normal

Tags: notabug

Found in version 24.4

Done: Stefan Monnier <monnier <at> iro.umontreal.ca>

Bug is archived. No further changes may be made.

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From: Jay Belanger <jay.p.belanger <at> gmail.com>
To: 19025 <at> debbugs.gnu.org
Cc: jay.p.belanger <at> gmail.com
Subject: bug#19025: 24.4; precision error when adding two floats
Date: Tue, 11 Nov 2014 20:28:49 -0600

>> (message "%s" (+ 379.744 57.93))
>>
>> The above prints 437.67400000000004.  Same if I use 57.930, but if I
>> use 57.931 (below) I get the correct answer 437.675.
>>  
>> (message "%s" (+ 379.744 57.931))
>>
>> I was able to work around by using format:
>>  
>> (message "%s" (format "%f" (+ 379.744 57.93)))
>>
>> which prints 437.674000.
>>  
>> FYI, I can replicate the issue with Emacs 21.3.1.
>
> Isn't this an artifact of the nature of floating-point arithmetic, rather than
> an issue with Emacs per se?

Yes, although it probably wouldn't be a bad idea to point out this issue
in the Elisp documentation.
This bug report was last modified 10 years and 196 days ago.

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