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Re: comparing floating point numbers

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BCFD36 <bcfd36@cruzio.com> writes:
>>> if (b == 0.0 && (a == 0.25 || a == -0.75))
>>
>> Comparing floating point numbers for equality is almost always a bug.
>> Only singular values like 0.0 are usually safe.
>
> Agreed. And anyone who made it past the 1st Intro to CS class would
> know that. I've no idea of the Original Poster's background so I
> wasn't going to speculate on his training. I'm pretty sure english is
> a 2nd language for him so what he asked and what he meant to ask were
> not quite the same. I can't fault someone for that.
>
> But, yes, comparing floats for equality is not a good thing.

... unless checking for the aforementioned "singular values", resulting
from simple assignment rather than calculation, and known to have a
representation that cannot suffer from precision loss etc.

The latter _is_ perfectly fine, which is why, for instance, a simplistic
compiler warning to complain about floating-point equality comparison
isn't so useful...

-miles

-- 
Brain, n. An apparatus with which we think we think.

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Thread

comparing floating point numbers Adam Majewski <adammaj1@o2.pl> - 2012-01-29 19:48 +0100
  Re: comparing floating point numbers BCFD36 <bcfd36@cruzio.com> - 2012-01-29 11:02 -0800
    Re: comparing floating point numbers "MikeWhy" <boat042-nospam@yahoo.com> - 2012-01-29 13:25 -0600
      Re: comparing floating point numbers "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2012-01-29 20:40 +0100
    Re: comparing floating point numbers Adam Majewski <adammaj1@o2.pl> - 2012-01-30 18:03 +0100
  Re: comparing floating point numbers Marcel Müller <news.5.maazl@spamgourmet.com> - 2012-01-29 21:34 +0100
    Re: comparing floating point numbers BCFD36 <bcfd36@cruzio.com> - 2012-01-29 14:55 -0800
      Re: comparing floating point numbers Miles Bader <miles@gnu.org> - 2012-01-30 11:48 +0900
        Re: comparing floating point numbers Juha Nieminen <nospam@thanks.invalid> - 2012-01-30 14:53 +0000
    Re: comparing floating point numbers scott@slp53.sl.home (Scott Lurndal) - 2012-01-30 17:22 +0000
      Re: comparing floating point numbers Robert Wessel <robertwessel2@yahoo.com> - 2012-01-30 13:55 -0600
      Re: comparing floating point numbers glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-13 01:56 +0000
  Re: comparing floating point numbers LR <lruss@superlink.net> - 2012-01-29 18:30 -0500
    Re: comparing floating point numbers Thomas Boell <tboell@domain.invalid> - 2012-01-30 16:29 +0100
  Re: comparing floating point numbers Christian Gollwitzer <auriocus@gmx.de> - 2012-01-30 08:07 +0100
    Re: comparing floating point numbers glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-13 01:59 +0000
  Re: comparing floating point numbers Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-01-30 06:26 -0800

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