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88 lines
1.9 KiB
JavaScript
88 lines
1.9 KiB
JavaScript
15 years ago
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dojo.provide("dojox.encoding.compression.lzw");
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dojo.require("dojox.encoding.bits");
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(function(){
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var _bits = function(x){
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var w = 1;
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for(var v = 2; x >= v; v <<= 1, ++w);
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return w;
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};
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dojox.encoding.compression.lzw.Encoder = function(n){
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this.size = n;
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this.init();
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};
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dojo.extend(dojox.encoding.compression.lzw.Encoder, {
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init: function(){
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this.dict = {};
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for(var i = 0; i < this.size; ++i){
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this.dict[String.fromCharCode(i)] = i;
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}
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this.width = _bits(this.code = this.size);
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this.p = "";
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},
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encode: function(value, stream){
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var c = String.fromCharCode(value), p = this.p + c, r = 0;
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// if already in the dictionary
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if(p in this.dict){
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this.p = p;
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return r;
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}
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stream.putBits(this.dict[this.p], this.width);
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// if we need to increase the code length
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if((this.code & (this.code + 1)) == 0){
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stream.putBits(this.code++, r = this.width++);
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}
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// add new string
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this.dict[p] = this.code++;
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this.p = c;
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return r + this.width;
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},
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flush: function(stream){
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if(this.p.length == 0){
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return 0;
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}
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stream.putBits(this.dict[this.p], this.width);
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this.p = "";
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return this.width;
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}
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});
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dojox.encoding.compression.lzw.Decoder = function(n){
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this.size = n;
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this.init();
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};
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dojo.extend(dojox.encoding.compression.lzw.Decoder, {
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init: function(){
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this.codes = new Array(this.size);
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for(var i = 0; i < this.size; ++i){
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this.codes[i] = String.fromCharCode(i);
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}
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this.width = _bits(this.size);
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this.p = -1;
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},
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decode: function(stream){
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var c = stream.getBits(this.width), v;
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if(c < this.codes.length){
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v = this.codes[c];
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if(this.p >= 0){
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this.codes.push(this.codes[this.p] + v.substr(0, 1));
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}
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}else{
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if((c & (c + 1)) == 0){
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this.codes.push("");
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++this.width;
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return "";
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}
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var x = this.codes[this.p];
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v = x + x.substr(0, 1);
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this.codes.push(v);
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}
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this.p = c;
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return v;
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}
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});
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})();
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