LZW compression: Difference between revisions

Content added Content deleted

Inline

@@ Line 1,751: / Line 1,751: @@
 =={{header|EMal}}==
 <syntaxhighlight lang="emal">
+type LzwCompression
-fun compress = List by text uncompressed
+fun compress ← List by text uncompressed
-  Map dictionary = text%int[].with(256, <int i|text%int(chr(i) => i))
+  List output ← int[]
-  text w
+  text working ← Text.empty
-  List result = int[]
+  Map symbolTable ← text%int[].with(256, <int i|text%int(chr(i) => i))
   for each text c in uncompressed
-    text wc = w + c
+    text augmented ← working + c
-	if dictionary.has(wc)
+	if symbolTable.has(augmented)
-	  w = wc
+	  working ← augmented
 	else
+	  symbolTable.insert(augmented, symbolTable.length)
-	  result.append(dictionary[w])
+	  int i ← symbolTable[working]
-	  dictionary.insert(wc, dictionary.length)
+	  output.append(i)
-	  w = c
+	  working ← c
-    end
+	end
   end
-  if not w.isEmpty() do result.append(dictionary[w]) end
+  if not working.isEmpty()
+    int i ← symbolTable[working]
-  return result
+	output.append(i)
-end
+  end
-fun decompress = text by List compressed
+  return output
-  Map dictionary = int%text[].with(256, <int i|int%text(i => chr(i)))
+end
-  text w = chr(compressed[0])
+fun decompress ← text by List compressed
-  text result = *w
+  Map symbolTable ← int%text[].with(256, <int i|int%text(i => chr(i)))
-  for each int k in compressed.extract(1)
+  text working ← symbolTable[compressed[0]]
-    text entry
+  text output ← *working
-    if dictionary.has(k)
+  for each int i in compressed.extract(1)
-      entry = dictionary[k]
+    text s
-    else if k == dictionary.length
+    if symbolTable.has(i)
-      entry = w + w[0]
+      s ← symbolTable[i]
+    else if i æ symbolTable.length # cScSc problem
+      s ← working + working[0]
     else
 	  error(65, "Error decompressing")
     end
-    result.append(entry)
+    output.append(s)
-    dictionary.insert(dictionary.length, w + entry[0])
+    symbolTable.insert(symbolTable.length, working + s[0])
-    w = entry
+    working ← s
   end
-  return result
+  return output
 end
 List compressed = compress("TOBEORNOTTOBEORTOBEORNOT")