Some helper functions (crc16 module dependency).

utils.py

@@ -0,0 +1,50 @@
+# -*- coding: utf-8 -*-
+'''
+    librfid - RFID EPC Class 1 Gen2 / ISO/IEC 18000-6C compliant library
+
+    Copyright (C) 2013  Entr'ouvert
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as
+    published by the Free Software Foundation, either version 3 of the
+    License, or (at your option) any later version.
+
+    This program 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 Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+    Helper functions
+'''
+
+
+import crc16
+from binascii import unhexlify
+
+from _exceptions import OverheadException
+
+
+def get_length_on_2_bytes(string):
+    length = len(string)
+    fmt = '%%0%dx' % (16 // 4)
+    return unhexlify(fmt % length)
+
+def get_integer_on_two_bytes(integer):
+    if integer > 65535:
+        raise OverheadException('Integer to big to be converted in a string '
+            'of two bytes')
+    fmt = '%%0%dx' % (16 // 4)
+    return unhexlify(fmt % integer)
+
+def get_crc_16_CCITT(string):
+    # Polynome x16 + x12 + x5 + 1, 0x1021
+    crc = crc16.crc16xmodem(string, 0xffff)
+    fmt = '%%0%dx' % (16 // 4)
+    return unhexlify(fmt % crc)
+
+def switch_big_to_little_indian(string):
+    return string[::-1]