From: William James <w_a_x_man@...>
Date: 2007-09-01T07:05:05+09:00
Subject: Re: 0.06 == 0.06 returns false in Ruby?

On Aug 31, 1:25 am, Michael Ulm <michael....@isis-papyrus.com> wrote:

> 2 Always use
>   (x-y).abs < (x.abs + y.abs) * Float::EPSILON)
>   as a test for equality.
>
>   Better than the first proposal, but won't work if the rounding error
>   gets too large after a complex computation.
>   In addition, (1) and (2) suffer from the problem that x==y and y==z do
>   not imply x==z.

How about
  (a - b).abs / [a, b].map{|x| a.abs}.min < Float::EPSILON
?

def eq( a, b )
  (a - b).abs / [a, b].map{|x| a.abs}.min < Float::EPSILON
end

DATA.each{|s|
  strings = s.chomp.split(";")
  floats = strings.map{|s| eval(s) }
  puts strings.join( " == " ) +
    " : #{floats[0]==floats[1]}  #{ eq( *floats ) }"
}

__END__
(0.05+0.01);0.06
(0.34+0.01);0.35
9.123456789;9.1234567891
9.123456789012345;9.1234567890123451
9.12345678901234e-9;9.123456789012341e-9

=== output ===
(0.05+0.01) == 0.06 : false  true
(0.34+0.01) == 0.35 : false  true
9.123456789 == 9.1234567891 : false  false
9.123456789012345 == 9.1234567890123451 : false  true
9.12345678901234e-9 == 9.123456789012341e-9 : false  true