#!/usr/athena/bin/perl

use strict;

sub gray;

# get arguments
my $n = shift;
my $nstop = shift;

# defaults
$nstop = $n, $n = 0 if ($nstop == undef);
$nstop = 256 if ($nstop == undef);

# bounds check
$n = 0 if ($n < 0);
$nstop = 0 if ($nstop < 0);

print $n . "\t" . gray ($n++) . "\n" while ($n <= $nstop);

exit;

sub gray {
    
    my $n = shift;
    return ((2 * $n) ^ ($n));

}