#!/usr/bin/perl -w

use strict;

package SCX::CRC;

our @crctable;

sub import {
	return if @crctable;

	my @table = (0x31);

	for my $i (1..7) {
		my $n = 2 * $table[-1];
		push @table, $n > 0xff ? ($n ^ 0x31) & 0xff: $n;
	}

	@crctable = (0x00);

#	print "Table = ", join(' ', map { sprintf("%02x", $_) } @table), "\n";

	for my $i (0x01 .. 0xff) {
		$crctable[$i] ^= $table[0] if $i & 0x01;
		$crctable[$i] ^= $table[1] if $i & 0x02;
		$crctable[$i] ^= $table[2] if $i & 0x04;
		$crctable[$i] ^= $table[3] if $i & 0x08;
		$crctable[$i] ^= $table[4] if $i & 0x10;
		$crctable[$i] ^= $table[5] if $i & 0x20;
		$crctable[$i] ^= $table[6] if $i & 0x40;
		$crctable[$i] ^= $table[7] if $i & 0x80;
	}

#	print "CRCtable = ", join(' ', map { sprintf("%02x", $_) } @crctable), "\n";
}

sub digest_str {
	my ($str) = @_;

	return digest(unpack("C*", $str));

}

sub digest {
	my (@bytes) = @_;

	my $res = 0;

	for my $byte (@bytes) {
		my $idx = $byte ^ $res;
		$res = $crctable[$idx];
	}

	return $res ^ 0xbb;
}

1;