From: "Peña, Botp" <botp@...>
Date: 2004-09-01T11:49:12+09:00
Subject: Re: (Final) [PATCH] Subtle bug in bignum.c

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