[ruby-core:54485] [Backport 200 - Backport #8299][Rejected] Minor error in float parsing

Issue #8299 has been updated by naruse (Yui NARUSE).

Status changed from Open to Rejected

marcandre (Marc-Andre Lafortune) wrote:
> Actually, this is a bug.
> 
> 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.

> 2) Float#to_s must be platform independent

double calculation itself is platform dependent.
see also x87 and if you want ruby for x86 to behave as x64 specify -msse2 -mfpmath=sse for gcc.
http://en.wikipedia.org/wiki/X87
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Backport #8299: Minor error in float parsing
https://bugs.ruby-lang.org/issues/8299#change-38791

Author: bobjalex (Bob Alexander)
Status: Rejected
Priority: Normal
Assignee: 
Category: 
Target version: 


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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