Bitwise negation Post: 302117985

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Top Forums Shell Programming and Scripting Bitwise negation Post 302117985 by dLloydm on Thursday 17th of May 2007 01:37:45 PM

05-17-2007

Registered User

This has been very helpful. It reveals to me that UNIX is storing signed integer values just like most programming languages I am familiar with. The leading 1's for negative numbers would indicate that the highest order bit is a sign bit. Therefore 2#1010 is 10 and -2#1010 is -10 which would be represented as:
111....1110110 - depending on the bit size used.

Therefore I am suspecting the course is not correct when it claims ((~ 2#1001)) evaluates to 2#110, but that it actually evaluates to:
"-2#1010".

If UNIX used unsigned integers in this case then it would evaluate to a very large number depending on the bit size used. Something like 2#111...11110110. From your analysis I do not suspect this is the case.

There is one more thing I would like to verify. The course has the following question:
What do you think is the output of the following piece of code?
((x = 2#1101 & 2#110))
((y = ~x))
print - $y

The answer given is 11, as in decimal eleven or 2#1011.
From what I understand I think the answer should be -5 as in -2#101.

I plan to inform the course provider of these possible issues but I would like to make sure there is an issue. Thanks for your help.

dLloydm

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file::homedir::unix

File::HomeDir::Unix(3)					User Contributed Perl Documentation				    File::HomeDir::Unix(3)

NAME

       File::HomeDir::Unix - Find your home and other directories on legacy Unix

SYNOPSIS

	 use File::HomeDir;

	 # Find directories for the current user
	 $home	  = File::HomeDir->my_home;	   # /home/mylogin
	 $desktop = File::HomeDir->my_desktop;	   # All of these will...
	 $docs	  = File::HomeDir->my_documents;   # ...default to home...
	 $music   = File::HomeDir->my_music;	   # ...directory
	 $pics	  = File::HomeDir->my_pictures;    #
	 $videos  = File::HomeDir->my_videos;	   #
	 $data	  = File::HomeDir->my_data;	   #

DESCRIPTION

       This module provides implementations for determining common user directories.  In normal usage this module will always be used via
       File::HomeDir.

SUPPORT

       See the support section the main File::HomeDir module.

AUTHORS

       Adam Kennedy <adamk@cpan.org>

       Sean M. Burke <sburke@cpan.org>

SEE ALSO

       File::HomeDir, File::HomeDir::Win32 (legacy)

COPYRIGHT

       Copyright 2005 - 2011 Adam Kennedy.

       Some parts copyright 2000 Sean M. Burke.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

       The full text of the license can be found in the LICENSE file included with this module.

perl v5.16.3							    2012-10-19						    File::HomeDir::Unix(3)