--- guess-crc.pl	2008/09/28 22:17:22	11
+++ guess-crc.pl	2008/09/29 16:28:49	12
@@ -9,13 +9,37 @@
 use Digest::CRC qw(crc32 crc16 crcccitt crc crc8);
 use Data::Dump qw/dump/;
 
+my $debug = 1 if @ARGV;
+
 sub hex2b {
 	my $hex = shift;
 	return map { hex($_) } split(/\s+/, $hex);
 }
 
-my @poly;
-# ( 32833, 43271, 32833, 43271, 19299, 35925, 47123, 49319, 56971 );
+my @check_polys = ( 0x0000 .. 0xffff );
+@check_polys = ( 32833, 43271, 32833, 43271, 19299, 35925, 47123, 49319, 56971 );
+
+my @check_offset = ( 0,1,2,3 );
+@check_offset = ( 1 ); # skip first, second always zero
+
+my $found_polys;
+
+sub check_crc {
+	my ( $poly, $bytes, $wanted ) = @_;
+	my $ctx = Digest::CRC->new(
+		#width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>0x1021, refin=>0 # ccitt
+		#width=>16, init=>0,      xorout=>0, refout=>1, poly=>0x8005, refin=>1 # crc16
+		#0x8408,
+		#0xa001,
+		width=>16, init=>0, xorout=>0, refout=>1, poly=>$poly,refin=>1
+		#width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>$poly, refin=>0 # ccitt
+	);
+	$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;
+}
 
 foreach (
 'D5 00 05 04 00 11 8C 66',
@@ -26,37 +50,24 @@
 
 	my $bytes = pack('H*', substr($hex, 0, -4));
 
-	warn "?? crc ",substr($hex,-4);
+	warn "?? guess crc ",substr($hex,-4);
 	my $crc   = pack('H4', substr($hex,-4));
 
 	warn "input $_ => ",dump( $bytes, $crc );
 
-	foreach my $o ( 0,1,2,3 ) {
+	foreach my $o ( @check_offset ) {
 		my $b = substr( $bytes, $o );
 
-		foreach my $poly ( 0x0000 .. 0xffff ) {
+		foreach my $poly ( @check_polys ) {
 
 			print "## poly $poly\n" if $poly % 1000 == 0;
 
-			my $ctx = Digest::CRC->new(
-				#width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>0x1021, refin=>0 # ccitt
-				#width=>16, init=>0,      xorout=>0, refout=>1, poly=>0x8005, refin=>1 # crc16
-				#0x8408,
-				#0xa001,
-				width=>16, init=>0, xorout=>0, refout=>1, poly=>$poly,refin=>1
-			);
-			$ctx->add( $b );
-			my $try = $ctx->digest;
-
-			my $v = pack('v*', $try);
-			my $n = pack('n*', $try);
-
-			if ( $v eq $crc or $n eq $crc ) {
-				warn "HIT: $o poly: $poly ",dump( $crc, $v, $n );
-				push @poly, $poly;
+			if ( check_crc( $poly, $b, $crc ) ) {
+				warn "HIT: $o poly: $poly\n";
+				$found_polys->{$poly}->{$o}++;
 			}
 		}
 	}
 }
 
-print "FOUND poly = ", dump( @poly );
+print "FOUND polys = ", dump( $found_polys );