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From: markb@agora.rain.com (Mark Biggar)
Newsgroups: comp.lang.perl
Subject: Re: Calculating XOR checksums? Fast splitting?
Message-ID: <1991Jun4.022321.5332@agora.rain.com>
Date: 4 Jun 91 02:23:21 GMT
References: <GNB.91Jun3135656@leo.bby.oz.au>
Organization: Open Communications Forum
Lines: 21

In article <GNB.91Jun3135656@leo.bby.oz.au> gnb@bby.oz.au (Gregory N. Bond) writes:
>Given a string, what is the fastest way to calculate the XOR of all
>bytes?  here is what I used:
>
>    $bcc = 0;
>    grep ($bcc ^= $_, unpack("C" x length($sc_data), $sc_data));

try folding the string in half.  Assumeing ther is a vec() in the program
somewhere the following should work:

$i = length($sc_data);
while ($j = int(($i+1)/2)) {
	($sc_data, $a) = unpack("A$j A$j", $sc_data);
	$sc_data ^= $a;
	$i = $j;
}

--
Perl's maternal uncle
Mark Biggar
markb@agora.rain.com