initial commit

python/hamming.py

@@ -0,0 +1,75 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+"""
+This module provides encoding and decoding functions for Hamming codes
+
+(C) 2022 Louis Heredero  louis.heredero@edu.vs.ch
+"""
+
+class HammingError(Exception):
+    pass
+
+def encode(data, blocksize=7):
+    result = []
+    datasize = blocksize-blocksize.bit_length()
+    data = list(map(int, data))
+    if len(data) % datasize:
+        raise HammingError(f"Length of data is not a multiple of {datasize}")
+
+    nblocks = int(len(data)/datasize)
+
+    for b in range(nblocks):
+        for i in range(blocksize):
+            # Power of 2
+            if (i+1)&i == 0 or i == 0:
+                result.append(0)
+
+            else:
+                result.append(data.pop(0))
+
+        for i in range(blocksize.bit_length()):
+            p = 1 << i
+            c = sum([result[b*blocksize+j] for j in range(blocksize) if (j+1)&p])
+            if c%2:
+                result[b*blocksize+p-1] = 1
+
+    return "".join(list(map(str, result)))
+
+def decode(data, blocksize=7):
+    result = []
+    datasize = blocksize-blocksize.bit_length()
+    data = list(map(int, data))
+    if len(data) % blocksize:
+        raise HammingError(f"Length of data is not a multiple of {blocksize}")
+
+    nblocks = int(len(data)/blocksize)
+    errors = 0
+
+    for b in range(nblocks):
+        pos = 0
+        for i in range(blocksize.bit_length()):
+            p = 1 << i
+            c = sum([data[b*blocksize+j] for j in range(blocksize) if (j+1)&p])
+            if c%2:
+                pos |= p
+
+        if pos != 0:
+            if pos > blocksize:
+                raise HammingError("Too many errors")
+                return
+
+            errors += 1
+            data[b*blocksize+pos-1] = 1-data[b*blocksize+pos-1]
+
+        for i in range(1, blocksize):
+            if (i+1)&i != 0:
+                result.append(data[b*blocksize+i])
+    
+    return "".join(list(map(str, result))), errors
+
+if __name__ == "__main__":
+    #print("10011010")
+    print(encode("10011010"))
+    #print(decode("011100101010"))
+    print(decode("00110011011010101101001010101011010101010111001100110011"))
+    print(decode("01000011011010101100001010101011110101000111001100111011"))