From: Markus <markus@...>
Date: 2004-09-01T14:06:48+09:00
Subject: Re: (Final) [PATCH] Subtle bug in bignum.c

>From what we've been able to determine (and I believe this is the
correct explanation) the problem only arises when garbage collection
occurs in the middle of the Bignum::& operation.  If you have more free
memory it may take many more passes for you to see the problem.

Another possibility: what version of Ruby are you running?

The doubled "{{" typo is very odd.  It was a single "{" in the original,
but you are correct, the "{" is doubled in the mail as received.

-- Markus

On Tue, 2004-08-31 at 19:49, "Pe単a, Botp" wrote:
> Markus [mailto:markus@reality.com] wrote:
> [snip]
> > Run the following script.  It should produce no output (and 
> > occasionally this is what happens).  But frequently, the 
> > values of a and b differ. 
> > This should not happen, but it does.  I have reproduced the 
> > problem on several different machines, running several 
> > different flavors of linux. 
> > 
> > 10.times {
> >     (0x10000..0x20000).each { |i|
> >         a = (i*-12345) & 0xFFFFFFFF
> >         b = (i*-12345) & 0xFFFFFFFF
> >         print "#{i.to_s(2)}  #{a.to_s(2)}  #{b.to_s(2)}\n" if a != b
> >         }
> >     }
> 
> I _cannot_ reproduce the problem (running winxp). I have run it and even
> looping it 10 times of your 10. Maybe I should loop more?
> 
> > 
> > A similar problem can b shown with bitwise-or
> > 
> > 
> > 10.times {
> >     (0x10000..0x20000).each { |i|
> >         a = (i*-12345) | 0
> >         b = (i*-12345) | 0
> >         print "#{i.to_s(2)}  #{a.to_s(2)}  #{{b.to_s(2)}\n" if a != b
> 
>                               small typo here ^^^^
> 
> 
> >         }
> >     }
> > 
> > 
> > But the problem does NOT occur with bitwise-xor:
> > 
> > 10.times {
> >     (0x10000..0x20000).each { |i|
> >         a = (i*-12345) ^ 0
> >         b = (i*-12345) ^ 0
> >         print "#{i.to_s(2)}  #{a.to_s(2)}  #{{b.to_s(2)}\n" if a != b
> 
>                               small typo here ^^^^
> 
> 
> 
> >         }
> >     }
> > [snip]
> > I used GCC 3.2.2 & 3.3.2 when compiling ruby, from otherwise 
> > unmodified 1.8.1 sources.  I looked in CVS and saw no post 
> > 1.8.1 changes that appeared relevant.
> >  
> > -- Markus (MQR) Roberts
> > 
> 
> kind regards -botp