From: Chris Shea <cmshea@...>
Date: 2007-04-18T06:20:12+09:00
Subject: Re: Bug in Float? (was: NaN Error)

On Apr 17, 12:41 pm, "Tim Pease" <tim.pe...@gmail.com> wrote:
> I ran across some peculiar behavior yesterday when working with large
> floating point values. Here is a small script that demonstrates the
> behavior. My question is, is this the expected behavior or is this a
> bug in Float?
>
> > cat float_bug.rb
>
> puts "ruby #{RUBY_VERSION} " +
>      "(#{RUBY_RELEASE_DATE} patchlevel #{RUBY_PATCHLEVEL}) " +
>      "[#{RUBY_PLATFORM}]"
>
> puts "Float::MAX = #{Float::MAX}"
> puts "1.0e+300 = #{1.0e+300}"
> puts "1.0e+301 = #{1.0e+301}"
> puts "1.0e+308 = #{1.0e+308}"
> puts "1.0e+700 = #{1.0e+700}"
>
> # EOF
>
> When I run this script on my Windows machine, it produces the output I
> would expect -- i.e. numbers above Float::MAX are "Infinity" and
> numbers below Float::MAX are valid floating point numbers.
>
> > ruby -w float_bug.rb
>
> ruby 1.8.5 (2006-12-25 patchlevel 12) [i386-cygwin]
> Float::MAX = 1.79769313486232e+308
> 1.0e+300 = 1.0e+300
> 1.0e+301 = 1.0e+301
> 1.0e+308 = 1.0e+308
> 1.0e+700 = Infinity
>
> Now, when I run the exact same script on a Solaris machine, some odd
> things start to happen
>
> > ruby -w float_bug.rb
>
> ruby 1.8.5 (2006-12-25 patchlevel 12) [sparc-solaris2.8]
> Float::MAX = 1.79769313486232e+308
> 1.0e+300 = 1.0e+300
> 1.0e+301 = NaN
> 1.0e+308 = NaN
> 1.0e+700 = 8.55180271847103e+116
>
> Whey are valid floats being treated as NaN?  Better yet, why does
> 1.0e+700 get evaluated to 8.5518027e+116?
>
> Once more on the Windows 1-click installed version of Ruby.
>
> > ruby -w float_bug.rb
>
> ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]
> Float::MAX = 1.79769313486232e+308
> 1.0e+300 = 1.0e+300
> 1.0e+301 = NaN
> 1.0e+308 = NaN
> 1.0e+700 = 1.0e+189
>
> Any thoughts on this one?  I encourage you to copy the float_bug.rb
> script and try it out for yourself.
>
> Blessings,
> TwP

On OS X 10.4.9

mvb:~ cms$ ruby float_bug.rb
ruby 1.8.6 (2007-03-13 patchlevel 0)
Float::MAX = 1.79769313486232e+308
1.0e+300 = 1.0e+300
1.0e+301 = NaN
1.0e+308 = NaN
1.0e+700 = 0.0

And my Xubuntu box (pre-RUBY_PATCHLEVEL apparently):

ruby 1.8.4 (2005-12-24)[i486-linux]
Float::MAX = 1.79769313486232e+308
1.0e+300 = 1.0e+300
1.0e+301 = 1.0e+301
1.0e+308 = 1.0e+308
1.0e+700 = 0.0