From: "Peña, Botp" <botp@...>
Date: 2007-06-22T12:03:28+09:00
Subject: Re: Ruby doesn't know how to multiply

From: Michael W. Ryder [mailto:_mwryder@worldnet.att.net] :
# My simple calculator is more precise for some math operations than my 
# expensive PC.  Maybe we need to implement something like 
# General Decimal 
# Arithmetic which is available for C++ and Java at 
# http://www2.hursley.ibm.com/decimal/ in Ruby.  It may be as simple as 
# writing wrappers for the operations, I haven't had to time to look 
# closer at the package.

have you tried bigdecimal?

irb(main):001:0> require 'bigdecimal'
=> true
irb(main):002:0> a=BigDecimal("14.95")
=> #<BigDecimal:2867a5c,'0.1495E2',8(8)>
irb(main):003:0> b=BigDecimal("0.6")
=> #<BigDecimal:28614b8,'0.6E0',4(8)>
irb(main):004:0> c=BigDecimal("8.97")
=> #<BigDecimal:28e47b4,'0.897E1',8(8)>
irb(main):005:0> d=BigDecimal("8.970000001")
=> #<BigDecimal:28dffe8,'0.8970000001E1',16(16)>
irb(main):006:0> a*b == c
=> true
irb(main):007:0> a*b == d
=> false
irb(main):008:0> c == 8.97
=> true

bigdecimal notation is very handy for calculator-like applications since the raw input usually is of type string.

kind regards -botp