tool to find correct byte for 8-bit XOR CRC

diff --git a/tools/xorcheck.py b/tools/xorcheck.py
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+++ b/tools/xorcheck.py
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+#!/usr/bin/python
+
+#  xorcheck.py - find xor values for 8-bit CRC
+# 
+#  Adam Laurie <adam@algroup.co.uk>
+#  http://rfidiot.org/
+# 
+#  This code is copyright (c) Adam Laurie, 2009, All rights reserved.
+#  For non-commercial use only, the following terms apply - for all other
+#  uses, please contact the author:
+#
+#    This code is free software; you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License as published by
+#    the Free Software Foundation; either version 2 of the License, or
+#    (at your option) any later version.
+#
+#    This code is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+
+import sys
+import os
+
+if(len(sys.argv) < 3):
+       print
+       print sys.argv[0] + ' - generate final byte for XOR CRC'
+       print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <CRC>'
+       print
+       print '\tSpecifying the bytes of a UID with a known CRC will generate the last byte value'
+       print '\tneeded to generate that CRC with a rolling XOR. All bytes should be specified in HEX.'
+       print
+       print 'Example:'
+       print
+       print '\txorcheck.py 04 00 80 64 ba'
+       print
+       print 'Should produce the output:'
+       print
+       print '\tTarget matched with Byte value: 5A'
+       print
+       os._exit(True)
+
+target= int(sys.argv[len(sys.argv) - 1],16)
+
+for candidate in range(256):
+       crc= 0x00
+       for i in range(len(sys.argv) - 2):
+               crc ^= int(sys.argv[i + 1],16)
+       crc ^= candidate
+       if (crc == target):
+               print
+               print 'Target matched with Byte value: %02X' % candidate
+               print
+