From: "Shot (Piotr Szotkowski)" <shot@...>
Date: 2007-12-01T01:08:26+09:00
Subject: Re: Bizarre Floating point errors in Ruby? Serious bug?

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MenTaLguY:

> On Thu, 29 Nov 2007 06:03:21 +0900, "Shot (Piotr Szotkowski)" <shot@hot.p=
l> wrote:

>> space.ship.traveller@gmail.com:

>>> >>> print (-140.14 * 100)
>>> -14014.0

>>> Well, actually this is the correct answer.... i.e. the result we are
>>> looking for if we were using real math. But, it is not the correct
>>> way to round 14013.999999, which is the actual value that we get with
>>> floating point math...

>> Why isn=E2=80=99t it? I might have learned basic math years ago, but to
>> me -14013.999999 rounded to one decimal place is exactly -14014.0
>> (it=E2=80=99s also -14014.00 when rounded to two decimal places, as well=
 as
>> -14014 when rounded to integers).

> This comes up a lot, and I guess the thing that most people have
> a hard time wrapping their heads around here is the fact that floating
> point numbers don't obey the laws of basic math -- not exactly.

Just to clarify =E2=80=93 I wasn=E2=80=99t writing anyhing about the ramifi=
cations of
IEEE 754, I was just pointing out that -14014.0 *is* the proper rounded
version of -14013.999999, so there=E2=80=99s no bug in how Ruby rounds the
IEEE 754 floats.

For anyone finding this thread in their pursuit of =E2=80=98but *why* Ruby
floats seem broken sometimes?=E2=80=99, a good starting point might be
this Wikipedia entry: http://en.wikipedia.org/wiki/IEEE_754-1985

-- Shot (=E2=80=98that=E2=80=99s no bug, it=E2=80=99s a spac^H^H^H^H^Hn IEE=
E float!=E2=80=99)
--=20
 <Black_Dog> "^\\([^ ()]+\\)\\(([0-9]+\\),\\([0-9]+\\))"
 <Black_Dog> gotta love regexps
<Bl1tz|work> it looks like some elaborate Japanese smiley
<Bl1tz|work> like "your parents just found out you've been
             slacking in class and you also have the flu"

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