compression_alcomp.py

import math from fractions import Fraction class ArithmeticCoding: def encode(self, string, dic, dic2): l = len(string) for i in range(1, l): probnow = dic[string[:i]] prob = dic2[string[i-1: i+1]] dic[string[:i+1]] = (Fraction(probnow[0] + (probnow[1] - probnow[0]) * prob[0]), Fraction(probnow[0] + (probnow[1] - probnow[0]) * prob[1])) i = string print(i, dic[i], (dic[i][0] + (dic[i][1]-dic[i][0])/2)) return dic def bitrate(self, dic, string): print(float(dic[string][0]), float(dic[string][1])) return -math.log(dic[string][1] - dic[string][0], 2) def generatecode(self, groupes): str1 = '' for i in groupes: string = str(i[0]) index = i[1] while index: lo = 1 str2 = string while index >= lo * 2: str2 = str2 + str2 lo *= 2 index -= lo str1 = str1 + str2 return str1 if __name__ == '__main__': dicPro = {'0': (0, 1/2), '1': (1/2, 1)} dicMKV = {'00': (0, 63/64), '11': (1/64, 1), '10': (0, 1/64), '01': (63/64, 1)} a = ArithmeticCoding() string2 = a.generatecode(((0, 13), (1, 11), (0, 10), (1, 15), (0, 14), (1, 9))) #print(len(string2)) string1 = '00000111' newdic = a.encode(string1, dicPro, dicMKV) for i in newdic: print(i, (newdic[i][0], newdic[i][1])) i = string1 print(-math.log(float(newdic[i][1]) - float(newdic[i][0]), 2)) #print(a.bitrate(newdic, string1)) #print('\n')