From: noreply@...
Date: 2006-10-25T22:59:37+09:00
Subject: [ ruby-Bugs-6314 ] Bitwise inversion of 32 bit numbers with most significant bit set results in overflow

Bugs item #6314, was opened at 2006-10-25 08:59
You can respond by visiting: 
http://rubyforge.org/tracker/?func=detail&atid=1698&aid=6314&group_id=426

Category: Core
Group: 1.9.x
Status: Open
Resolution: None
Priority: 3
Submitted By: Ian Roddis (ian_roddis)
Assigned to: Nobody (None)
Summary: Bitwise inversion of 32 bit numbers with most significant bit set results in overflow

Initial Comment:
Tested using nightly snapshot and 1.8.5 stable:

# ./ruby -v
ruby 1.9.0 (2006-10-23) [i686-linux]
#./ruby -e 'a= "7fffff00".hex ; b= "ffffff00".hex ; printf "%b => %b\n", a, ~a ; printf "%b => %b\n", b, ~b'
1111111111111111111111100000000 => ..10000000000000000000000011111111
11111111111111111111111100000000 => ..1

Case 1: A number with bit 32 (most significant) not set. No overflow.
Case 2: A number with bit 32 set. Overflow observed.

This may be caused by the right-shifting of a VALUE type (unsigned long) during the inversion process.

Workaround: use XOR 0xffffffff instead.

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You can respond by visiting: 
http://rubyforge.org/tracker/?func=detail&atid=1698&aid=6314&group_id=426