From 0cee287283b3e867d6db404035ca1a0c055ecf5f Mon Sep 17 00:00:00 2001
From: Szymon Wojciechowski <szywoj3@st.amu.edu.pl>
Date: Wed, 20 Jun 2018 15:28:24 +0000
Subject: [PATCH] Dodaj 'crc16.py'

---
 crc16.py | 139 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 crc16.py

diff --git a/crc16.py b/crc16.py
new file mode 100644
index 0000000..bd75c00
--- /dev/null
+++ b/crc16.py
@@ -0,0 +1,139 @@
+import sys
+import ast
+import time
+from itertools import zip_longest
+
+class Polynomial:
+
+    def __init__(self, coef_list):
+        self.degree = len(coef_list) - 1
+        self.coefficients = coef_list
+
+    @staticmethod
+    def add(p1, p2):
+        result = []
+        f = p1.coefficients
+        g = p2.coefficients
+        if len(f) >= len(g):
+            result = f
+            for i in range(0, len(g)):
+                result[i] = f[i] + g[i]
+        else:
+            result = g
+            for i in range(0, len(f)):
+                result[i] = f[i] + g[i]
+        result = [x % int(n) for x in result]        
+        return Polynomial(result)             
+
+    @staticmethod
+    def multiply(p1, p2):
+        result = [0] * (p1.degree + p2.degree + 1)
+        f = p1.coefficients
+        g = p2.coefficients
+        for i in range(0, len(f)):
+            for j in range(0, len(g)):
+                result[i+j] += f[i] * g[j]
+        result = [x % int(n) for x in result]
+        return Polynomial(result)
+
+    @staticmethod
+    def divide(p1, p2):          
+        def inverse(x):
+            for i in range(1, int(n)):
+                r = (i * x) % int(n)
+                if r == 1:
+                    break
+            else:
+                raise ZeroDivisionError
+            return i       
+        if p1.degree < p2.degree:
+            return p1
+        f = p1.coefficients
+        g = p2.coefficients
+        g_lead_coef = g[-1]
+        g_deg = p2.degree
+        while len(f) >= len(g):
+            f_lead_coef = f[-1]
+            tmp_coef = f_lead_coef * inverse(g_lead_coef)
+            tmp_exp = len(f) - 1 - g_deg
+            tmp = []
+            for _ in range(tmp_exp):
+                tmp.append(0)
+            tmp.append(tmp_coef)
+            tmp_poly = Polynomial(tmp)
+            sub = Polynomial.multiply(p2, tmp_poly)
+            f = [x - y for x, y in zip(f, sub.coefficients)]
+            f = [x % int(n) for x in f]
+            while f and f[-1] == 0:
+                f.pop()
+        return Polynomial(f)
+
+
+n = 2
+
+
+def normalize_byte(data):
+    while len(data) != 8:
+        if len(data) < 8:
+            data = str(0) + data
+        else:
+            data.replace(data[0], '')
+    return data
+
+
+def encode(in_data):
+    data = in_data
+    data = list(data)
+    data_binary = [bin(ord(char)).replace('b', '') for char in data]
+    data_binary = [normalize_byte(byte) for byte in data_binary]
+    data_binary = [int(bit) for bit in list(''.join(data_binary))]
+    data_binary.reverse()
+
+    M = [0] * 16 + data_binary
+    L = [0] * (len(data_binary)) + [1] * 16
+    G = [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1]
+    FCS_poly = Polynomial.divide(Polynomial.add(Polynomial(M), Polynomial(L)), Polynomial(G))
+    FCS = FCS_poly.coefficients + [0] * (16 - len(FCS_poly.coefficients))
+
+    FCS.reverse()
+    data_binary.reverse()
+    data_binary = data_binary + FCS
+    data_binary = [data_binary[i:i+8] for i in range(0, len(data_binary), 8)]
+    data = [chr(int(''.join(map(str, byte)), 2)) for byte in data_binary]
+
+    return ''.join(data)
+
+
+def check_fcs(in_data):
+    data = in_data
+    data = list(data)
+    data_binary = [bin(ord(char)).replace('b', '') for char in data]
+    data_binary = [normalize_byte(byte) for byte in data_binary]
+    data_binary = [int(bit) for bit in list(''.join(data_binary))]
+    data_binary.reverse()
+
+    C = [0] * 16 + data_binary
+    L = [0] * len(data_binary) + [1] * 16
+    G = [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1]
+    S = Polynomial.divide(Polynomial.add(Polynomial(C), Polynomial(L)), Polynomial(G))
+
+    if S.coefficients == []:
+        return True
+
+    return False
+
+
+def main():
+    try:
+        if sys.argv[1] == '-e' or sys.argv[1] == '-encode':
+            print(encode(sys.argv[2]))
+        elif sys.argv[1] == '-c' or sys.argv[1] == '-check':
+            print(check_fcs(sys.argv[2]))
+        else:
+            raise IndexError
+    except IndexError:
+        print("To encode: python3 CRC16.py -e [argument]\nTo check FCS: python3 CRC16.py -c [argument]")
+
+
+if __name__ == "__main__":
+    main()