[ruby-core:56236] [ruby-trunk - Bug #8697] Fixnum complement operator issue

Issue #8697 has been updated by mame (Yusuke Endoh).


=begin
I guess you mistake "the ones' complement of a binary number" for "the ones' complement system".
The former is a kind of operation for the binary representation of a number, no matter what the number itself is.
The latter gives a mapping that corresponds the binary representations to mathematical numbers.

> See related articles on Wikipedia: ((<One's complement|URL:http://en.wikipedia.org/wiki/Ones%27_complement>))

Actually it says:

> The ones' complement of a binary number is defined as the value obtained by inverting all the bits in the binary representation of the number

For example, the bit pattern of +0 is "all 0s" in both ones' and twos' complement systems.
By the definition above, applying the ones' complement to +0 yields a number whose binary representation is "all 1s".

This number that has "all 1" bit pattern represents -0 in ones' complement system, and -1 in twos' complement system.
Ruby's Integer uses twos' complement system.

Even without knowledge of it, "the ones' complement of 0 is -1", is very common phrase in the computer science.  There is nothing wrong in both the implementation and documentation of Fixnum#~.
=end
----------------------------------------
Bug #8697: Fixnum complement operator issue
https://bugs.ruby-lang.org/issues/8697#change-40726

Author: torimus (Torimus GL)
Status: Feedback
Priority: Normal
Assignee: 
Category: core
Target version: current: 2.1.0
ruby -v: 1.9.3p448
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


=begin
By the ((<documentation|URL:http://www.ruby-doc.org/core-2.0/Fixnum.html#method-i-7E>)), bitwise complement operator ((*~*)) to Fixnum instance should do ((*one's complement*)) with just flipping all bits. In fact, current implementation does ((*two's complement*)) due to or-ing with FIXNUM_FLAG, which is defined as 1.

Either fix the documentation or the fix_rev function implementation.
Affected versions: both 1.9.3 and 2.0.0
=end



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