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

Status changed from Rejected to Open
ruby -v set to trunk

naruse (Yui NARUSE) wrote:
> > 1) Float#to_s must be minimal while round-tripping. This is clearly not the case in the given examples.
> 
> If the given value cannot be represented by binary, it won't be minimal while round-tripping.

Sorry, I do not understand what you said. What I meant to say is ([ruby-core:30145]):

For any float f, the two following conditions should hold:
(1) f.to_s.to_f == f        (round trips)
(2) f.to_s.chop.to_f != f   (minimal)

The second condition is a simplification; if the string representation is in scientific notation, than the character to remove would be the one just before the "e". Also, if the string representation ends with ".0", then it is minimal.

> > 2) Float#to_s must be platform independent
> 
> double calculation itself is platform dependent.

Sorry, I should have specified "...on IEEE 754 platforms", which is the case for mgwin32, right?

> Moreover there's non IEEE-754 fp for example VAX.

We don't support VAX, as you wrote yourself in [ruby-core:42077], so how is this relevant exactly?
----------------------------------------
Bug #8299: Minor error in float parsing
https://bugs.ruby-lang.org/issues/8299#change-38801

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'




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