dpack/packer_lzw.js

   1 /*
   2  * packer/unpacker code derived from JavaScript O Lait library (jsolait)
   3  * JavaScript O Lait library(jsolait): Copyright (c) 2003-2006 Jan-Klaas Kollhof, GNU LGPL v2.1+
   4  *
   5  * modified by Ketmar // Avalon Group
   6 */
   7 function LZWPack (str) {
   8   var dict = {};
   9   var data = (str+"").split("");
  10   var out = [];
  11   var currChar;
  12   var phrase = data[0];
  13   var code = 256;
  14
  15   for (var i = 1; i < data.length; i++) {
  16     currChar = data[i];
  17     if (dict[phrase+currChar] != null) phrase += currChar;
  18     else{
  19       out.push(phrase.length>1?dict[phrase]:phrase.charCodeAt(0));
  20       dict[phrase+currChar] = code;
  21       code++;
  22       phrase = currChar;
  23     }
  24   }
  25   out.push(phrase.length>1?dict[phrase]:phrase.charCodeAt(0));
  26
  27   var res = "";
  28
  29   function AddCode (c) {
  30     if (c >= 32 && c <= 126) {
  31       if (c == 34 || c == 92) res += '\\';
  32       res += String.fromCharCode(c);
  33     } else {
  34       var h = c.toString(16).toLowerCase();
  35       while (h.length < 2) h = "0"+h;
  36       if (h.length == 2) res += "\\x"+h;
  37       else {
  38         while (h.length < 4) h = "0"+h;
  39         res += "\\u"+h;
  40       }
  41     }
  42   }
  43
  44   for (var i = 0; i < out.length; i++) AddCode(out[i]);
  45   return res;
  46 }
  47
  48
  49 function LZWUnpack (str) {
  50   var dict = {};
  51   var data = (str+"").split("");
  52   var currChar = data[0];
  53   var oldPhrase = currChar;
  54   var out = [currChar];
  55   var code = 256;
  56   var phrase;
  57   for (var i = 1; i < data.length; i++) {
  58     var currCode = data[i].charCodeAt(0);
  59     if (currCode < 256) phrase = data[i];
  60     else phrase = dict[currCode]?dict[currCode]:(oldPhrase+currChar);
  61     out.push(phrase);
  62     currChar = phrase.charAt(0);
  63     dict[code] = oldPhrase+currChar;
  64     code++;
  65     oldPhrase = phrase;
  66   }
  67   var s = out.join("");
  68   var res = [];
  69   for (var f = 0; f < s.length; f++) res.push(s.charCodeAt(f));
  70   return res;
  71 }
  72
  73
  74 function PackArray (arr) {
  75   var s = "";
  76   for (var f = 0; f < arr.length; f++) s += String.fromCharCode(arr[f]);
  77   return LZWPack(s);
  78 }
  79
  80
  81 function DUnpackStr (s) {
  82   return LZWUnpack(s);
  83 }