--- guess-crc.pl	2008/09/29 16:28:49	12
+++ guess-crc.pl	2008/10/01 18:45:35	13
@@ -4,10 +4,29 @@
 #
 # 09/28/08 21:54:24 CEST Dobrica Pavlinusic <dpavlin@rot13.org>
 
+# CRC info from: http://stackoverflow.com/questions/149617/how-could-i-guess-a-checksum-algorithm
+# and from: http://www.geocities.com/SiliconValley/Pines/8659/crc.htm
+
+# LRC:    Polynomial=0x81; 8 bits; Normal; Initial=0; Final=as calculated
+# CRC16:  Polynomial=0xa001; 16 bits; Normal; Initial=0; Final=as calculated
+# CCITT:  Polynomial=0x1021; 16 bits; reverse; Initial=0xffff; Final=0x1d0f
+# Xmodem: Polynomial=0x1021; 16 bits; reverse; Initial=0; Final=0x1d0f
+# CRC32:  Polynomial=0xebd88320; 32 bits; Normal; Initial=0xffffffff; Final=inverted value
+# ZIP32:  Polynomial=0x04c11db7; 32 bits; Normal; Initial=0xffffffff; Final=as calculated
+
+# IPX:  Polynomial=0x8005; 16 bits; Reverse; Initial=0xffff; Final=as calculated
+# ISO 18000-6B: Polynomial=0x1021; 16 bits; Reverse; Initial=0xffff; Final=as calculated
+# ISO 18000-6C: Polynomial=0x1021; 16 bits; Reverse; Initial=0xffff; Final=as calculated
+#	Data must be padded with zeroes to make a multiple of 8 bits
+# ISO CRC5: Polynomial=custom; 5 bits; Reverse; Initial=0x9; Final=shifted left by 3 bits
+#   Data must be padded with zeroes to make a multiple of 8 bits
+# EPC class 1: Polynomial=custom 0x1021; 16 bits; Reverse; Initial=0xffff; Final=post processing of 16 zero bits
+
 use strict;
 
 use Digest::CRC qw(crc32 crc16 crcccitt crc crc8);
 use Data::Dump qw/dump/;
+use File::Slurp;
 
 my $debug = 1 if @ARGV;
 
@@ -17,11 +36,25 @@
 }
 
 my @check_polys = ( 0x0000 .. 0xffff );
-@check_polys = ( 32833, 43271, 32833, 43271, 19299, 35925, 47123, 49319, 56971 );
+#@check_polys = ( 32833, 43271, 32833, 43271, 19299, 35925, 47123, 49319, 56971 );	# crc16
+@check_polys = ( 31125, 53345, 11642, 24337, 51699, 55122, 15257 ); # ccitt
 
 my @check_offset = ( 0,1,2,3 );
 @check_offset = ( 1 ); # skip first, second always zero
 
+my @try_polys = (
+{ name => "CRC-16/CITT", width => 16, poly => 0x1021, init => 0xFFFF, refin => 0, refout => 0, xorout => 0x0000 },
+{ name => "XMODEM",      width => 16, poly => 0x8408, init => 0x0000, refin => 1, refout => 1, xorout => 0x0000 },
+{ name => "ARC",         width => 16, poly => 0x8005, init => 0x0000, refin => 1, refout => 1, xorout => 0x0000 },
+{ name => "CRC-16",      width => 16, poly => 0xA001, init => 0x0000, refin => 0, refout => 0, xorout => 0x0000 },
+);
+
+my @data = (
+'D5 00 05 04 00 11 8C 66',
+'D6 00 05 FE 00 05 FA 40',
+);
+#@data = read_file('all.out') if -e 'all.out';
+
 my $found_polys;
 
 sub check_crc {
@@ -31,29 +64,28 @@
 		#width=>16, init=>0,      xorout=>0, refout=>1, poly=>0x8005, refin=>1 # crc16
 		#0x8408,
 		#0xa001,
-		width=>16, init=>0, xorout=>0, refout=>1, poly=>$poly,refin=>1
-		#width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>$poly, refin=>0 # ccitt
+		#width=>16, init=>0, xorout=>0, refout=>1, poly=>$poly,refin=>1 # crc16
+		width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>$poly, refin=>0 # ccitt
 	);
 	$ctx->add( $bytes );
 	my $try = $ctx->digest;
-	my $str = pack('n*', $try);
-	warn "## check_crc( $poly, ",dump($bytes)," ) = ",dump( $str, $wanted ) if $debug;
-	return $str eq $wanted;
+	my $n = pack('n*', $try);
+	my $v = pack('n*', $try);
+	warn "## check_crc( $poly, ",dump($bytes)," ) = ",dump( $n, $v, $wanted ) if $debug;
+	return $n eq $wanted || $v eq $wanted;
 }
 
-foreach (
-'D5 00 05 04 00 11 8C 66',
-'D6 00 05 FE 00 05 FA 40',
-) {
+foreach ( @data ) {
+
 	my $hex = $_;
 	$hex =~ s/\s+//g;
 
 	my $bytes = pack('H*', substr($hex, 0, -4));
 
-	warn "?? guess crc ",substr($hex,-4);
+	print "?? guess crc ",substr($hex,-4),"\n";
 	my $crc   = pack('H4', substr($hex,-4));
 
-	warn "input $_ => ",dump( $bytes, $crc );
+	warn "input $_ => ",dump( $bytes, $crc ) if $debug;
 
 	foreach my $o ( @check_offset ) {
 		my $b = substr( $bytes, $o );