GNU bug report logs - #5114
23.1.50; (string-to-number (number-to-string most-positive-fixnum))

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Package: emacs;

Reported by: Helmut Eller <eller.helmut <at> gmail.com>

Date: Thu, 3 Dec 2009 15:05:07 UTC

Severity: normal

Tags: fixed

Fixed in version 24.1

Done: Lars Magne Ingebrigtsen <larsi <at> gnus.org>

Bug is archived. No further changes may be made.

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Message #10 received at 5114 <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 5114 <at> debbugs.gnu.org
Subject: Re: bug#5114: 23.1.50; (string-to-number (number-to-string most-positive-fixnum))
Date: Thu, 03 Dec 2009 15:52:16 -0500

> (setq x (string-to-number (number-to-string most-positive-fixnum)))
> (= most-positive-fixnum x) => nil
   
> x is 2305843009213693440 but it should be most-positive-fixnum
> which is 2305843009213693951.

> The test
> (= most-positive-fixnum 
>    (string-to-number (number-to-string most-positive-fixnum)))
> seems to work as expected on 32-bit machines but not so on 64 bit.

Indeed, it passes through a floating point conversion, so there's only
abour 52 bit of precesion.


        Stefan
This bug report was last modified 13 years and 290 days ago.

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