git.pond.sub.org Git - eow/blob - static/dojo-release-1.1.1/dojox/encoding/compression/lzw.js

   1 if(!dojo._hasResource["dojox.encoding.compression.lzw"]){ //_hasResource checks added by build. Do not use _hasResource directly in your code.
   2 dojo._hasResource["dojox.encoding.compression.lzw"] = true;
   3 dojo.provide("dojox.encoding.compression.lzw");
   4 dojo.require("dojox.encoding.bits");
   5
   6 (function(){
   7         var _bits = function(x){
   8                 var w = 1;
   9                 for(var v = 2; x >= v; v <<= 1, ++w);
  10                 return w;
  11         };
  12
  13         dojox.encoding.compression.lzw.Encoder = function(n){
  14                 this.size = n;
  15                 this.init();
  16         };
  17
  18         dojo.extend(dojox.encoding.compression.lzw.Encoder, {
  19                 init: function(){
  20                         this.dict = {};
  21                         for(var i = 0; i < this.size; ++i){
  22                                 this.dict[String.fromCharCode(i)] = i;
  23                         }
  24                         this.width = _bits(this.code = this.size);
  25                         this.p = "";
  26                 },
  27                 encode: function(value, stream){
  28                         var c = String.fromCharCode(value), p = this.p + c, r = 0;
  29                         // if already in the dictionary
  30                         if(p in this.dict){
  31                                 this.p = p;
  32                                 return r;
  33                         }
  34                         stream.putBits(this.dict[this.p], this.width);
  35                         // if we need to increase the code length
  36                         if((this.code & (this.code + 1)) == 0){
  37                                 stream.putBits(this.code++, r = this.width++);
  38                         }
  39                         // add new string
  40                         this.dict[p] = this.code++;
  41                         this.p = c;
  42                         return r + this.width;
  43                 },
  44                 flush: function(stream){
  45                         if(this.p.length == 0){
  46                                 return 0;
  47                         }
  48                         stream.putBits(this.dict[this.p], this.width);
  49                         this.p = "";
  50                         return this.width;
  51                 }
  52         });
  53
  54         dojox.encoding.compression.lzw.Decoder = function(n){
  55                 this.size = n;
  56                 this.init();
  57         };
  58
  59         dojo.extend(dojox.encoding.compression.lzw.Decoder, {
  60                 init: function(){
  61                         this.codes = new Array(this.size);
  62                         for(var i = 0; i < this.size; ++i){
  63                                 this.codes[i] = String.fromCharCode(i);
  64                         }
  65                         this.width = _bits(this.size);
  66                         this.p = -1;
  67                 },
  68                 decode: function(stream){
  69                         var c = stream.getBits(this.width), v;
  70                         if(c < this.codes.length){
  71                                 v = this.codes[c];
  72                                 if(this.p >= 0){
  73                                         this.codes.push(this.codes[this.p] + v.substr(0, 1));
  74                                 }
  75                         }else{
  76                                 if((c & (c + 1)) == 0){
  77                                         this.codes.push("");
  78                                         ++this.width;
  79                                         return "";
  80                                 }
  81                                 var x = this.codes[this.p];
  82                                 v = x + x.substr(0, 1);
  83                                 this.codes.push(v);
  84                         }
  85                         this.p = c;
  86                         return v;
  87                 }
  88         });
  89 })();
  90
  91 }