Path: utzoo!mnetor!tmsoft!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!uunet!rbj
From: rbj@uunet.UU.NET (Root Boy Jim)
Newsgroups: comp.lang.perl
Subject: Even Parity Table Generation
Message-ID: <121817@uunet.UU.NET>
Date: 9 Feb 91 03:08:56 GMT
Organization: UUNET Communications Services, Falls Church, VA
Lines: 32

I needed an even parity table, so I decided to generate it recursively.
I thought people might be interested in my solution, and or
commenting on how it might be done better. And while I'm at it,
I hereby request another function: chr(), the opposite of ord().
Either that, or get rid of ord. Anyway, here it is:

print time,"\n"; &mkEven(7);
print time,"\n"; &prtEven;
print time,"\n"; exit(0);

sub mkEven # global %even (level)
{
    local($_,$k) = @_;
    $_ || return $even{"\0"} = "\0";            # bottom out
    &mkEven(--$_);                              # lower half
    $_ = 1 << $_;                               # next bit
    for $k (keys %even) {                       # key loop
        $even{pack('c',$_^ord($k))} =           # new key
            pack('c',128^$_^ord($even{$k}));    # new value
    }
}

sub prtEven
{
    for (sort keys(%even)) {
        printf("%x %x\n",ord($_),ord($even{$_}));
    }
}
-- 
	Root Boy Jim Cottrell <rbj@uunet.uu.net>
	I got a head full of ideas
	They're driving me insane