From: Yukihiro Matsumoto <matz@...>
Date: 2011-01-08T09:20:53+09:00
Subject: [ruby-core:34242] Re: [Ruby 1.9-Bug#4248][Open] r30483 might cause underflow

Hi,

In message "Re: [ruby-core:34218] [Ruby 1.9-Bug#4248][Open] r30483 might cause underflow"
    on Fri, 7 Jan 2011 21:21:00 +0900, Yusuke Endoh <redmine@ruby-lang.org> writes:

|Hi, matz (or Ray Chason) --
|
|http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=30483
|
|> Author: matz
|> Date: Fri Jan 7 00:17:06 2011 UTC (9 hours, 45 minutes ago)
|> Log Message:
|> * bignum.c (bigmul1_karatsuba): avoid overflow that make assertion
|>   fail in certain case.  this patch is contributed from Ray Chason
|>   <chasonr at gmail.com> in personal communication.
|
|
|I understand the possibility that zds may cause overflow, right?
|Do you have the "certain case", or can you disclose the "personal
|communication" ?

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)