[483] | 1 | define([ |
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| 2 | "dojo/_base/lang", // dojo.extend |
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| 3 | "../bits" |
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| 4 | ], function(lang, bits) { |
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| 5 | |
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| 6 | var lzw = lang.getObject("dojox.encoding.compression.lzw", true); |
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| 7 | |
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| 8 | var _bits = function(x){ |
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| 9 | var w = 1; |
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| 10 | for(var v = 2; x >= v; v <<= 1, ++w); |
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| 11 | return w; |
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| 12 | }; |
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| 13 | |
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| 14 | lzw.Encoder = function(n){ |
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| 15 | this.size = n; |
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| 16 | this.init(); |
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| 17 | }; |
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| 18 | |
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| 19 | lang.extend(lzw.Encoder, { |
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| 20 | init: function(){ |
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| 21 | this.dict = {}; |
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| 22 | for(var i = 0; i < this.size; ++i){ |
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| 23 | this.dict[String.fromCharCode(i)] = i; |
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| 24 | } |
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| 25 | this.width = _bits(this.code = this.size); |
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| 26 | this.p = ""; |
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| 27 | }, |
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| 28 | encode: function(value, stream){ |
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| 29 | var c = String.fromCharCode(value), p = this.p + c, r = 0; |
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| 30 | // if already in the dictionary |
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| 31 | if(p in this.dict){ |
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| 32 | this.p = p; |
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| 33 | return r; |
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| 34 | } |
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| 35 | stream.putBits(this.dict[this.p], this.width); |
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| 36 | // if we need to increase the code length |
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| 37 | if((this.code & (this.code + 1)) == 0){ |
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| 38 | stream.putBits(this.code++, r = this.width++); |
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| 39 | } |
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| 40 | // add new string |
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| 41 | this.dict[p] = this.code++; |
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| 42 | this.p = c; |
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| 43 | return r + this.width; |
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| 44 | }, |
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| 45 | flush: function(stream){ |
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| 46 | if(this.p.length == 0){ |
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| 47 | return 0; |
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| 48 | } |
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| 49 | stream.putBits(this.dict[this.p], this.width); |
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| 50 | this.p = ""; |
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| 51 | return this.width; |
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| 52 | } |
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| 53 | }); |
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| 54 | |
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| 55 | lzw.Decoder = function(n){ |
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| 56 | this.size = n; |
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| 57 | this.init(); |
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| 58 | }; |
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| 59 | |
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| 60 | lang.extend(lzw.Decoder, { |
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| 61 | init: function(){ |
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| 62 | this.codes = new Array(this.size); |
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| 63 | for(var i = 0; i < this.size; ++i){ |
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| 64 | this.codes[i] = String.fromCharCode(i); |
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| 65 | } |
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| 66 | this.width = _bits(this.size); |
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| 67 | this.p = -1; |
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| 68 | }, |
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| 69 | decode: function(stream){ |
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| 70 | var c = stream.getBits(this.width), v; |
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| 71 | if(c < this.codes.length){ |
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| 72 | v = this.codes[c]; |
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| 73 | if(this.p >= 0){ |
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| 74 | this.codes.push(this.codes[this.p] + v.substr(0, 1)); |
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| 75 | } |
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| 76 | }else{ |
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| 77 | if((c & (c + 1)) == 0){ |
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| 78 | this.codes.push(""); |
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| 79 | ++this.width; |
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| 80 | return ""; |
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| 81 | } |
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| 82 | var x = this.codes[this.p]; |
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| 83 | v = x + x.substr(0, 1); |
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| 84 | this.codes.push(v); |
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| 85 | } |
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| 86 | this.p = c; |
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| 87 | return v; |
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| 88 | } |
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| 89 | }); |
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| 90 | |
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| 91 | return lzw; |
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| 92 | }); |
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