Moving code around to help my understanding. file names most probably wrong right now but will update when understand it better

conversions.py

@@ -0,0 +1,59 @@
+###############################################################
+
+# Copyright (C) 2015 Junzi Sun (TU Delft)
+
+# This program 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 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# the polynominal generattor code for CRC
+import math
+
+GENERATOR = "1111111111111010000001001"
+
+def hex2bin(hexstr):
+    """Convert a hexdecimal string to binary string, with zero fillings. """
+    scale = 16
+    num_of_bits = len(hexstr) * math.log(scale, 2)
+    binstr = bin(int(hexstr, scale))[2:].zfill(int(num_of_bits))
+    return binstr
+
+def bin2int(binstr):
+    """Convert a binary string to integer. """
+    return int(binstr, 2)
+
+def crc(msg, encode=False):
+    """Mode-S Cyclic Redundancy Check
+    Detect if bit error occurs in the Mode-S message
+    Args:
+        msg (string): 28 bytes hexadecimal message string
+        encode (bool): True to encode the date only and return the checksum
+    Returns:
+        string: message checksum, or partity bits (encoder)
+    """
+
+    msgbin = list(hex2bin(msg))
+
+    if encode:
+        msgbin[-24:] = ['0'] * 24
+
+    # loop all bits, except last 24 piraty bits
+    for i in range(len(msgbin)-24):
+        # if 1, perform modulo 2 multiplication,
+        if msgbin[i] == '1':
+            for j in range(len(GENERATOR)):
+                # modulo 2 multiplication = XOR
+                msgbin[i+j] = str((int(msgbin[i+j]) ^ int(GENERATOR[j])))
+
+    # last 24 bits
+    reminder = ''.join(msgbin[-24:])
+    return reminder