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36 lines
976 B
Perl
Executable File
36 lines
976 B
Perl
Executable File
#!/usr/bin/perl
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die("Usage: crc <HEX-MESSAGE> <CRC>\n") if(int(@ARGV) != 2);
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my $msg = $ARGV[0];
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$msg =~ s/ //g;
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my $des = $ARGV[1];
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$des =~ s/ //g;
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# FFFF: 77 72 statt 2c 7f
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# FFFF: 5C AC statt DC D9
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#for(my $ic = 0; $ic < 65536; $ic++) {
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for(my $ic = 0; $ic < 2; $ic++) {
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my $crc = ($ic == 0?0:0xffffffff);
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for(my $i = 0; $i < length($msg); $i += 2) {
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my $n = ord(pack('H*', substr($msg, $i, 2)));
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my $od = $n;
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for my $b (0..7) {
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my $crcbit = ($crc & 0x80000000) ? 1 : 0;
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my $databit = ($n & 0x80) ? 1 : 0;
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$crc <<= 1;
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$n <<= 1;
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$crc ^= 0x04C11DB7 if($crcbit != $databit);
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# printf("%3d.%d %02x CRC %x ($crcbit $databit)\n", $i/2, $b, $n, $crc);
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}
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# printf("%3d %02x CRC %02x %02x\n", $i/2, $od, ($crc&0xff00)>>8, $crc&0xff);
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}
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# print "$ic\n" if($ic % 10000 == 0);
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printf("%02x %02x\n",($crc&0xff00)>>8,$crc&0xff);
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print "got $ic\n"
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if(sprintf("%02x%02x",($crc&0xff00)>>8,$crc&0xff) eq $des);
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}
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