source: Dev/trunk/src/client/dojox/encoding/compression/lzw.js @ 533

define([
        "dojo/_base/lang",      // dojo.extend
        "../bits"
], function(lang, bits) {

        var lzw = lang.getObject("dojox.encoding.compression.lzw", true);

        var _bits = function(x){
                var w = 1;
                for(var v = 2; x >= v; v <<= 1, ++w);
                return w;
        };

        lzw.Encoder = function(n){
                this.size = n;
                this.init();
        };

        lang.extend(lzw.Encoder, {
                init: function(){
                        this.dict = {};
                        for(var i = 0; i < this.size; ++i){
                                this.dict[String.fromCharCode(i)] = i;
                        }
                        this.width = _bits(this.code = this.size);
                        this.p = "";
                },
                encode: function(value, stream){
                        var c = String.fromCharCode(value), p = this.p + c, r = 0;
                        // if already in the dictionary
                        if(p in this.dict){
                                this.p = p;
                                return r;
                        }
                        stream.putBits(this.dict[this.p], this.width);
                        // if we need to increase the code length
                        if((this.code & (this.code + 1)) == 0){
                                stream.putBits(this.code++, r = this.width++);
                        }
                        // add new string
                        this.dict[p] = this.code++;
                        this.p = c;
                        return r + this.width;
                },
                flush: function(stream){
                        if(this.p.length == 0){
                                return 0;
                        }
                        stream.putBits(this.dict[this.p], this.width);
                        this.p = "";
                        return this.width;
                }
        });

        lzw.Decoder = function(n){
                this.size = n;
                this.init();
        };

        lang.extend(lzw.Decoder, {
                init: function(){
                        this.codes = new Array(this.size);
                        for(var i = 0; i < this.size; ++i){
                                this.codes[i] = String.fromCharCode(i);
                        }
                        this.width = _bits(this.size);
                        this.p = -1;
                },
                decode: function(stream){
                        var c = stream.getBits(this.width), v;
                        if(c < this.codes.length){
                                v = this.codes[c];
                                if(this.p >= 0){
                                        this.codes.push(this.codes[this.p] + v.substr(0, 1));
                                }
                        }else{
                                if((c & (c + 1)) == 0){
                                        this.codes.push("");
                                        ++this.width;
                                        return "";
                                }
                                var x = this.codes[this.p];
                                v = x + x.substr(0, 1);
                                this.codes.push(v);
                        }
                        this.p = c;
                        return v;
                }
        });

        return lzw;
});