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Groups > comp.lang.python > #29692

Re: Exact integer-valued floats

From Paul Rubin <no.email@nospam.invalid>
Newsgroups comp.lang.python
Subject Re: Exact integer-valued floats
References <505ca3e9$0$29981$c3e8da3$5496439d@news.astraweb.com>
Date 2012-09-21 15:23 -0700
Message-ID <7xzk4j6mmq.fsf@ruckus.brouhaha.com> (permalink)
Organization Nightsong/Fort GNOX

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Steven D'Aprano <steve+comp.lang.python@pearwood.info> writes:
> Have I got this right? Is there a way to work out the gap between one 
> float and the next?

Yes, 53-bit mantissa as people have mentioned.  That tells you what ints
can be exactly represented.  But, arithmetic in some situations can have
a 1-ulp error.  So I wonder if it's possible that if n is large enough,
you might have something like n+1==n even if the integers n and n+1 have
distinct floating point representations.

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Thread

Exact integer-valued floats Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-21 17:29 +0000
  Re: Exact integer-valued floats Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-21 12:13 -0600
  Re: Exact integer-valued floats Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-09-21 22:47 +0300
  Re: Exact integer-valued floats Nobody <nobody@nowhere.com> - 2012-09-21 20:59 +0100
  Re: Exact integer-valued floats Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-21 16:26 -0400
    Re: Exact integer-valued floats Hans Mulder <hansmu@xs4all.nl> - 2012-09-21 23:04 +0200
      Re: Exact integer-valued floats Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-21 20:54 -0400
  Re: Exact integer-valued floats Alister <alister.ware@ntlworld.com> - 2012-09-21 21:14 +0000
  Re: Exact integer-valued floats Paul Rubin <no.email@nospam.invalid> - 2012-09-21 15:23 -0700
    Re: Exact integer-valued floats Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-22 01:36 +0000
      Re: Exact integer-valued floats Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-22 01:01 -0400
        Re: Exact integer-valued floats Tim Roberts <timr@probo.com> - 2012-09-22 14:05 -0700
          Re: Exact integer-valued floats Dave Angel <d@davea.name> - 2012-09-22 19:06 -0400
            Re: Exact integer-valued floats Hans Mulder <hansmu@xs4all.nl> - 2012-09-23 09:45 +0200
          Re: Exact integer-valued floats wrw@mac.com - 2012-09-24 11:29 -0400
    Re: Exact integer-valued floats Nobody <nobody@nowhere.com> - 2012-09-22 11:19 +0100

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