2w4nn46ep1zz4

hw2/bebey.md

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+

hw2/lzw_decoder.py

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+import math
+from sys import argv
+
+if len(argv) == 1:
+    print('Usage: python ' + argv[0] + ' inp_file [out_file]')
+    exit(-1)
+
+with open(argv[1], 'rb') as inp_file:
+    enc_str = inp_file.read()
+
+byte_cnt = 0
+dictionary = {i: [i] for i in range(256)}
+out = b''
+
+with open(argv[2] if len(argv) == 3 else argv[1][:-4], 'wb') as out_file:
+    cur_str, cur_sl = dictionary[enc_str[0]], 0
+    out_file.write(bytes(cur_str))
+    prev_str = cur_str
+    for entry in enc_str[1:]:
+        byte_cnt += 1
+        cur_sl = cur_sl + entry * 256 ** (byte_cnt - 1)
+        if byte_cnt < math.ceil(math.log2(len(dictionary) + 1) / 8):
+            continue
+        byte_cnt = 0
+        try:
+            dictionary[cur_sl]
+        except KeyError:
+            dictionary[len(dictionary)] = prev_str + [prev_str[0]]
+        cur_str, cur_sl = dictionary[cur_sl], 0
+        out_file.write(bytes(cur_str))
+        if prev_str + cur_str[:1] not in dictionary.values():
+            dictionary[len(dictionary)] = prev_str + cur_str[:1]
+        prev_str = cur_str