Constellations/js/Share/Decoder.js

49 lines
910 B
JavaScript

function Decoder(input) {
this.input = atob(input);
this.cache = 0;
this.size = 0;
}
Decoder.prototype.pop = function() {
if(this.size < 1) {
if(this.input.length < 1) {
return null;
} else {
this.cache = this.input.charCodeAt(0);
this.size = 8;
this.input = this.input.slice(1);
}
}
this.size--;
var wasFirstBitOne = this.cache > 0x7f;
this.cache = (2*this.cache) & 0xff;
return wasFirstBitOne ? 1 : 0;
};
Decoder.prototype.variableLength3 = function() {
if(this.pop() == 1) {
return this.pop() + 1;
} else {
return 0;
}
};
Decoder.prototype.variableLength6 = function() {
if(this.pop() == 1) {
return 2 + this.int(2);
} else {
return this.pop();
}
};
Decoder.prototype.int = function(size) {
var result = 0;
for(var i = 0; i < size; i++) {
result = 2*result + this.pop();
}
return result;
};
return {
make: function(input) {return new Decoder(input);}
};