From: Yusuke Endoh <redmine@...>
Date: 2011-01-09T01:44:09+09:00
Subject: [ruby-core:34259] [Ruby 1.9-Bug#4248][Rejected] r30483 might cause underflow

Issue #4248 has been updated by Yusuke Endoh.

Status changed from Open to Rejected

Hi,

2011/1/8 Yukihiro Matsumoto <matz@ruby-lang.org>:
> The following is the problem case given from Ray:
>
> def mul(len)
>   x = (1<<len) - 1
>   y = (1<<len) - 1
>   return x * y
> end
> puts '%X' % mul(2240)

Thank you.  I'll add a test case based on the code.


And, my suspicion was wrong; mrkn noted me that the patch does NOT
cause underflow since t3 = (xh+xl)*(yh+yl) >= xh*yh + xl*yl = t1 + t2.
So I'm withdrawing this ticket.  Sorry.

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
http://redmine.ruby-lang.org/issues/show/4248

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