Data commit

Task/LZW-compression/EMal/lzw-compression.emal

@@ -0,0 +1,40 @@
+fun compress = List by text uncompressed
+  Map dictionary = text%int[].with(256, <int i|text%int(chr(i) => i))
+  text w
+  List result = int[]
+  for each text c in uncompressed
+    text wc = w + c
+	if dictionary.has(wc)
+	  w = wc
+	else
+	  result.append(dictionary[w])
+	  dictionary.insert(wc, dictionary.length)
+	  w = c
+    end	
+  end
+  if not w.isEmpty() do result.append(dictionary[w]) end
+  return result
+end
+fun decompress = text by List compressed
+  Map dictionary = int%text[].with(256, <int i|int%text(i => chr(i)))
+  text w = chr(compressed[0])
+  text result = *w
+  for each int k in compressed.extract(1)
+    text entry
+    if dictionary.has(k)
+      entry = dictionary[k]
+    else if k == dictionary.length
+      entry = w + w[0]
+    else
+	  error(65, "Error decompressing")
+    end
+    result.append(entry)
+    dictionary.insert(dictionary.length, w + entry[0])
+    w = entry
+  end
+  return result
+end
+List compressed = compress("TOBEORNOTTOBEORTOBEORNOT")
+writeLine(compressed)
+text decompressed = decompress(compressed)
+writeLine(decompressed)