From: Samuel Lown <me@...>
Date: 2009-05-06T10:01:54+09:00
Subject: Unexpected BigDecimal rounding issue

Hi,

Some more not so fun rounding issues.

Using Floats:

>> ((30 / 1.16) * 1.16) == 30
=> true

Cool, so you'd think it would work with BigDecimal:

>> ((30 / BigDecimal("1.16")) * BigDecimal("1.16")) == 30
=> false
>> ((30 / BigDecimal("1.16")) * BigDecimal("1.16")).to_s
=> "30.0000000000000000000000002"

I'm clearly missing something here as I thought BigDecimal was supposed
to fix this type of thing.

Tested in:
ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0]
ruby 1.9.1p0 (2009-01-30 revision 21907) [i386-darwin9.6.0]

Can anyone offer an explanation?

Cheers, sam
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