From: Tim Pease <tim.pease@...>
Date: 2007-04-18T03:41:22+09:00
Subject: Bug in Float? (was: NaN Error)

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