From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2013-04-22T01:58:53+09:00
Subject: [ruby-core:54495] [ruby-trunk - Bug #8299] Minor error in float parsing


Issue #8299 has been updated by marcandre (Marc-Andre Lafortune).


Can anyone on [i386-mingw32] report which of the two following is false:

    [-1.1505945e-05].pack('G') != [-1.1505945000000001e-05].pack('G')
    "\xBE\xE8!5\n\x1D\x17A".unpack('G').first.to_s == "-1.1505945e-05"

If the first is false, then parsing is buggy and I presume you get:

    f = "\xBE\xE8!5\n\x1D\x17A".unpack('G').first
    f.to_s.to_f == f # => false, should be true for any float f (not NaN or inf).

If the second is false, then conversion to string is buggy and I imagine you will get:

    f = -1.1505945e-05
    g = -1.1505945000000001e-05
    f == g # => false
    f.to_s == g.to_s # => true (should be consistent for any floats f & g (not NaN))
----------------------------------------
Bug #8299: Minor error in float parsing
https://bugs.ruby-lang.org/issues/8299#change-38802

Author: bobjalex (Bob Alexander)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: trunk
Backport: 


I encountered a float that either parses [slightly] differently (or converts to string differently) in Ruby than it does in Python or Java. This looks like a  Ruby bug since the result "looks" incorrect.

It is easily reproduced by entering the magic number (-1.1505945E-5) into irb. It behaves the same in 2.0 and 1.9. I'm using Windows.

Below is an irb session that demonstrates. Also included are JRuby and Python trials that show better behavior.

This issue is not causing me any problems, but just in case someone there is interested in looking into it...

Bob

>ruby -v
ruby 2.0.0p0 (2013-02-24) [i386-mingw32]

>irb
irb(main):001:0> RUBY_VERSION
=> "2.0.0"
irb(main):002:0> -1.1505945E-5
=> -1.1505945000000001e-05

>ruby19 -v
ruby 1.9.3p392 (2013-02-22) [i386-mingw32]

>irb19
irb(main):001:0> RUBY_VERSION
=> "1.9.3"
irb(main):002:0> -1.1505945E-5
=> -1.1505945000000001e-05
irb(main):002:0>

>jirb
irb(main):001:0> -1.1505945E-5
=> -1.1505945e-05

>python
Python 2.7.4rc1 (default, Mar 24 2013, 14:34:32) [MSC v.1500 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> -1.1505945E-5
-1.1505945e-05
>>> repr(-1.1505945E-5)
'-1.1505945e-05'




-- 
http://bugs.ruby-lang.org/