From: Shyouhei Urabe <shyouhei@...>
Date: 2011-09-13T21:19:51+09:00
Subject: [ruby-core:39518] [Ruby 1.9 - Bug #4576] Range#step miss the last value, if end-exclusive and has float number


Issue #4576 has been updated by Shyouhei Urabe.


Vit Ondruch wrote:
> Shyouhei Urabe wrote:
> > Vit Ondruch wrote:
> > > Please first see the commit [1] and then tell me why the original test case should fail?
> > 
> > Because no one guarantees that it should pass.
> 
> It is a feature I guess, there is even test case for this unfortunately, so why should something pass on one platform and should not pass on another? That doesn't make sense.

It is a hardware issue.  So it is quite natural for one platform behaves differently than another.

> > > Actually it fails on i386 and succeeds on x86_64 which is a bit suspicious.
> > 
> > It is a clear sign that you are "dancing with floats".
> > 
> > As Tomoyoki Chikanaga says in note #note-2 of this issue I believe this is a "learn floating point number" kind of thig.
> 
> No, it is not ... the main difference is if the float comparison is done in memory or in registers. Each have different precision and it popups on i386.

Yes, I know.  And you cannot force your C compiler to use specific hardware (except by compiler flags).  Your patch is insufficient for your needs.  In fact, C lacks a way to specify how a floating number should be handled.
----------------------------------------
Bug #4576: Range#step miss the last value, if end-exclusive and has float number
http://redmine.ruby-lang.org/issues/4576

Author: Joey Zhou
Status: Closed
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: -


=begin
Hi, I find that:

* if: range.exclude_end? == true
* and: any one in [begin_obj, end_obj, step] is a true Float(f.to_i != f)
* and: unless begin_obj + step*int == end_obj
* then: the result will miss the last value.

for example:

 p (1...6.3).step.to_a # => [1.0, 2.0, 3.0, 4.0, 5.0], no 6.0
 p (1.1...6).step.to_a # => [1.1, 2.1, 3.1, 4.1], no 5.1
 p (1...6).step(1.1).to_a # => [1.0, 2.1, 3.2, 4.300000000000001], no 5.4

 p (1.0...6.6).step(1.9).to_a # => [1.0, 2.9], no 4.8
 p (1.0...6.7).step(1.9).to_a # => [1.0, 2.9, 4.8]
 p (1.0...6.8).step(1.9).to_a # => [1.0, 2.9, 4.8], no 6.7

Maybe the #step is ok on integers, but there's something wrong if the range is end-exclusive and contain float numbers.
=end



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