- Author:
- David Nickerson <nickerso@users.sourceforge.net>
- Date:
- 2009-07-16 02:00:03+12:00
- Desc:
- the starting point for the HH tutorial example
- Permanent Source URI:
- https://models.fieldml.org/workspace/a1/rawfile/f6a8f90307388eb4b040ee3566b84d88b59247f7/dojo-presentation/js/dojo/dojox/encoding/compression/lzw.js
dojo.provide("dojox.encoding.compression.lzw");
dojo.require("dojox.encoding.bits");
(function(){
var _bits = function(x){
var w = 1;
for(var v = 2; x >= v; v <<= 1, ++w);
return w;
};
dojox.encoding.compression.lzw.Encoder = function(n){
this.size = n;
this.init();
};
dojo.extend(dojox.encoding.compression.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;
}
});
dojox.encoding.compression.lzw.Decoder = function(n){
this.size = n;
this.init();
};
dojo.extend(dojox.encoding.compression.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;
}
});
})();
