Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!lfcs!ajcd
From: ajcd@lfcs.ed.ac.uk (Angus Duggan)
Newsgroups: comp.lang.perl
Subject: Strange behaviour with | & ^ and associative arrays
Summary: perl bug when mixing bitwise operators and associative arrays
Keywords: perl, associative arrays, bitwise operators
Message-ID: <2957@castle.ed.ac.uk>
Date: 21 Mar 90 12:13:59 GMT
Reply-To: ajcd@lfcs.ed.ac.uk (Angus Duggan)
Organization: Laboratory for the Foundations of Computer Science, University of Edinburgh
Lines: 42

I've come across a problem which occurs when mixing bitwise operators with
associative array components; if the numeric value of an associative array
component is negative, it is converted to zero when the expression is
evaluated. The same thing does *not* happen for other arithmetic operators.
This also affects the bitwise assignment operators |=, &=, and ^= (I think;
last two untested). Try the script:

	#!/usr/local/bin/perl
	$fonts{"cmr10",300} = 1;
	# Correct values printed by following statement
	print STDOUT "Values are ", $fonts{"cmr10",300}, ",",
				    $fonts{"cmr10",300} - 0, ",",
				    $fonts{"cmr10",300} & 1, ",",
				    $fonts{"cmr10",300} | 0, "\n";
        $fonts{"cmr10",300} = -1;
	# Incorrect values printed by following statement
        print STDOUT "Values are ", $fonts{"cmr10",300}, ",",
				    $fonts{"cmr10",300} - 0, ",",
				    $fonts{"cmr10",300} & 1, ",",
				    $fonts{"cmr10",300} | 0, "\n";

The output of this script is:
	Values are 1,1,1,1
	Values are -1,-1,0,0

The second line should read:
	Values are -1,-1,1,-1

perl -v prints:
	$Header: perly.c,v 3.0.1.4 90/02/28 18:06:41 lwall Locked $
	Patch level: 15

This is being run on a Sun 3/50 with SunOS 4.0.?

In the instance in which it occurred, I can use || instead of |, but I'd
prefer not to. Anyone other workarounds welcome.

Angus
==
Angus Duggan, Department of Computer Science,	| #include <stddisclaimer.h>
University of Edinburgh, JCMB,			| USENET: ajcd@lfcs.ed.ac.uk
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