Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #93443

Re: Bug in floating point multiplication

Path csiph.com!usenet.pasdenom.info!news.redatomik.org!newsfeed.xs4all.nl!newsfeed7.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path <python@mrabarnett.plus.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.006
X-Spam-Evidence '*H*': 0.99; '*S*': 0.00; 'cpython': 0.05; 'happen.': 0.09; 'reports.': 0.09; 'subject:skip:m 10': 0.09; 'python': 0.11; '2.7': 0.13; '(needed': 0.16; 'from:addr:mrabarnett.plus.com': 0.16; 'from:addr:python': 0.16; 'from:name:mrab': 0.16; 'message- id:@mrabarnett.plus.com': 0.16; 'passed.': 0.16; 'received:192.168.1.4': 0.16; 'received:84.93': 0.16; 'received:84.93.230': 0.16; 'reproduce': 0.16; 'wrote:': 0.16; 'runs': 0.18; 'windows': 0.20; 'aug': 0.20; 'do.': 0.22; '2008,': 0.22; 'title,': 0.22; 'bit': 0.23; 'feb': 0.23; 'dec': 0.23; 'header:In-Reply-To:1': 0.24; 'url:bugs': 0.24; 'header:User- Agent:1': 0.26; 'skip:( 20': 0.28; 'prints': 0.29; 'correct': 0.29; "can't": 0.32; 'anyone': 0.32; 'probably': 0.32; 'received:84': 0.32; 'url:python': 0.33; "d'aprano": 0.33; 'steven': 0.33; '(for': 0.34; 'to:addr:python-list': 0.35; 'reply.': 0.35; 'url:org': 0.36; 'so,': 0.37; 'should': 0.37; 'operating': 0.37; 'subject:: ': 0.37; 'version': 0.38; '2010,': 0.39; 'to:addr:python.org': 0.39; 'system.': 0.39; 'received:192': 0.39; 'your': 0.60; 'necessarily': 0.61; 'more': 0.62; 'mar': 0.65; 'reply': 0.67; '2.5.4': 0.84; '8.1': 0.84; '2013,': 0.91; '2014,': 0.91
X-CM-Score 0.00
X-CNFS-Analysis v=2.1 cv=OoyysHLt c=1 sm=1 tr=0 a=0nF1XD0wxitMEM03M9B4ZQ==:117 a=0nF1XD0wxitMEM03M9B4ZQ==:17 a=0Bzu9jTXAAAA:8 a=EBOSESyhAAAA:8 a=AGkejYDSTmIA:10 a=IkcTkHD0fZMA:10 a=8AHkEIZyAAAA:8 a=NDGeRcRBYTOruNnhotUA:9 a=QEXdDO2ut3YA:10
X-AUTH mrabarnett@:2500
Date Thu, 02 Jul 2015 17:20:27 +0100
From MRAB <python@mrabarnett.plus.com>
User-Agent Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0
MIME-Version 1.0
To python-list@python.org
Subject Re: Bug in floating point multiplication
References <55955048$0$1662$c3e8da3$5496439d@news.astraweb.com>
In-Reply-To <55955048$0$1662$c3e8da3$5496439d@news.astraweb.com>
Content-Type text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding 7bit
X-BeenThere python-list@python.org
X-Mailman-Version 2.1.20+
Precedence list
List-Id General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive <http://mail.python.org/pipermail/python-list/>
List-Post <mailto:python-list@python.org>
List-Help <mailto:python-list-request@python.org?subject=help>
List-Subscribe <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups comp.lang.python
Message-ID <mailman.257.1435854219.3674.python-list@python.org> (permalink)
Lines 50
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1435854219 news.xs4all.nl 2889 [2001:888:2000:d::a6]:33044
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:93443

Show key headers only | View raw

On 2015-07-02 15:52, Steven D'Aprano wrote:
> Despite the title, this is not one of the usual "Why can't Python do
> maths?" "bug" reports.
>
> Can anyone reproduce this behaviour? If so, please reply with the version of
> Python and your operating system. Printing sys.version will probably do.
>
>
> x = 1 - 1/2**53
> assert x == 0.9999999999999999
> for i in range(1, 1000000):
>      if int(i*x) == i:
>          print(i); break
>
>
> Using Jython and IronPython, the loop runs to completion. That is the
> correct behaviour, or so I am lead to believe. Using Python 2.6, 2.7 and
> 3.3 on Centos and Debian, it prints 2049 and breaks. That should not
> happen. If you can reproduce that (for any value of i, not necessarily
> 2049), please reply.
>
> See also http://bugs.python.org/issue24546 for more details.
>
These are all on Windows 8.1 with CPython from www.python.org.

With "x = 1 - 1.0/2**53" (needed for Python 2.x) they all passed.

2.5.4 (r254:67916, Dec 23 2008, 15:19:34) [MSC v.1400 64 bit (AMD64)]
2.5.2 (r252:60911, Feb 21 2008, 13:11:45) [MSC v.1310 32 bit (Intel)]
2.6.6 (r266:84297, Aug 24 2010, 18:13:38) [MSC v.1500 64 bit (AMD64)]
2.6.5 (r265:79096, Mar 19 2010, 21:48:26) [MSC v.1500 32 bit (Intel)]
2.7.7 (default, Jun  1 2014, 14:21:57) [MSC v.1500 64 bit (AMD64)]
2.7.7 (default, Jun  1 2014, 14:17:13) [MSC v.1500 32 bit (Intel)]
3.1.4 (default, Jun 12 2011, 14:16:16) [MSC v.1500 64 bit (AMD64)]
3.1.4 (default, Jun 12 2011, 15:05:44) [MSC v.1500 32 bit (Intel)]
3.2.5 (default, May 15 2013, 23:07:10) [MSC v.1500 64 bit (AMD64)]
3.2.3 (default, Apr 11 2012, 07:15:24) [MSC v.1500 32 bit (Intel)]
3.3.5 (v3.3.5:62cf4e77f785, Mar  9 2014, 10:35:05) [MSC v.1600 64 bit 
(AMD64)]
3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit 
(Intel)]
3.4.2 (v3.4.2:ab2c023a9432, Oct  6 2014, 22:16:31) [MSC v.1600 64 bit 
(AMD64)]
3.4.2 (v3.4.2:ab2c023a9432, Oct  6 2014, 22:15:05) [MSC v.1600 32 bit 
(Intel)]
3.5.0b2 (v3.5.0b2:7a088af5615b, May 31 2015, 06:22:19) [MSC v.1900 64 
bit (AMD64)]
3.5.0b2 (v3.5.0b2:7a088af5615b, May 31 2015, 06:08:44) [MSC v.1900 32 
bit (Intel)]

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Bug in floating point multiplication Steven D'Aprano <steve@pearwood.info> - 2015-07-03 00:52 +1000
  Re: Bug in floating point multiplication Michael Poeltl <michael.poeltl@univie.ac.at> - 2015-07-02 17:10 +0200
  Re: Bug in floating point multiplication Chris Angelico <rosuav@gmail.com> - 2015-07-03 01:21 +1000
  Re: Bug in floating point multiplication Robin Becker <robin@reportlab.com> - 2015-07-02 16:24 +0100
  Re: Bug in floating point multiplication Paul Rubin <no.email@nospam.invalid> - 2015-07-02 08:26 -0700
    Re: Bug in floating point multiplication Chris Angelico <rosuav@gmail.com> - 2015-07-03 01:34 +1000
      Re: Bug in floating point multiplication Steven D'Aprano <steve@pearwood.info> - 2015-07-03 01:41 +1000
    Re: Bug in floating point multiplication Ian Kelly <ian.g.kelly@gmail.com> - 2015-07-02 09:38 -0600
  Re: Bug in floating point multiplication Vincent Vande Vyvre <vincent.vande.vyvre@telenet.be> - 2015-07-02 17:15 +0200
  Re: Bug in floating point multiplication Ian Kelly <ian.g.kelly@gmail.com> - 2015-07-02 09:28 -0600
  Re: Bug in floating point multiplication Robin Becker <robin@reportlab.com> - 2015-07-02 16:29 +0100
  Re: Bug in floating point multiplication Ian Kelly <ian.g.kelly@gmail.com> - 2015-07-02 09:32 -0600
  Re: Bug in floating point multiplication Steven D'Aprano <steve@pearwood.info> - 2015-07-03 01:42 +1000
  Re: Bug in floating point multiplication duncan smith <buzzard@invalid.invalid> - 2015-07-02 17:08 +0100
  Re: Bug in floating point multiplication MRAB <python@mrabarnett.plus.com> - 2015-07-02 17:20 +0100
  Re: Bug in floating point multiplication Tim Chase <python.list@tim.thechases.com> - 2015-07-02 11:59 -0500
  Re: Bug in floating point multiplication Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2015-07-02 19:49 +0200
    Re: Bug in floating point multiplication Ned Deily <nad@acm.org> - 2015-07-02 22:07 -0700
      Re: Bug in floating point multiplication Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2015-07-03 18:27 +0200
  Re: Bug in floating point multiplication Laurent Pointal <laurent.pointal@free.fr> - 2015-07-02 23:12 +0200
  Re: Bug in floating point multiplication Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-07-03 16:13 +0100
  Re: Bug in floating point multiplication Laura Creighton <lac@openend.se> - 2015-07-05 00:54 +0200
  Re: Bug in floating point multiplication Peter Otten <__peter__@web.de> - 2015-07-05 09:38 +0200

csiph-web