There is an extension library BigDecimal (part of Ruby 1.8)
_http://docs.warhead.org.uk/pkg-docs/ruby18/bigdecimal_en.html_
(http://docs.warhead.org.uk/pkg-docs/ruby18/bigdecimal_en.html)
which should work:
require "BigDecimal.rb"
a=Infinity
b=-Infinity