From: Heesob Park <phasis@...>
Date: 2009-03-07T13:15:36+09:00
Subject: Re: 2000-1992.2 - is this a known bug?

Hi,

2009/3/7 Christopher Dicely <cmdicely@gmail.com>:
> 2009/3/6 S2 <some.r@ndom.mail.invalid.net>:
>> ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
>>
>>>> 2000-1992.2
>> => 7.79999999999995
>>
>>
>
> The use of inexact floating point numbers by default in Ruby (which
> follows C and most, but not all, other programming languages) is a
> design choice, not a bug. One might dispute whether or not its a good
> design choice (personally, I prefer Scheme's numeric tower and exact
> numbers by default with conversion to inexact numbers only when an
> inexact operation is applied to an exact number or an explicit
> designation of an inexact number is given), but its a point about
> which people could debate endlessly, and since BigDecimal is at least
> in the standard library, its not a matter of whether Ruby can do exact
> math, but just how verbose the code is to do it.
>
> ex:
>
> require 'bigdecimal'
> require 'bigdecimal/math'
>
> class BigDecimal
>  # BigDecimal.to_s is ugly
>  def pretty
>    digits, magnitude = to_s.split('.')[1].split('E')
>    magnitude=magnitude.to_i
>    digits.insert(0,'0'*[(1-magnitude),0].max)
>    digits.insert([magnitude,1].min,'.')
>  end
> end
>
> include BigMath
>
> (2000-BigDecimal('1992.2')).pretty
> => "7.8"
>
Why not use BigDecimal.to_s('F') ?

Refer to http://www.ruby-doc.org/stdlib/libdoc/bigdecimal/rdoc/classes/BigDecimal.html#M000032


Regards,

Park Heesob