mediagoblin/extlib/thingiview.js/binaryReader.js

// BinaryReader
// Refactored by Vjeux <vjeuxx@gmail.com>
// http://blog.vjeux.com/2010/javascript/javascript-binary-reader.html

// Original
//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/classes/binary-parser [rev. #1]

BinaryReader = function (data) {
	this._buffer = data;
	this._pos = 0;
};

BinaryReader.prototype = {

	/* Public */

	readInt8:	function (){ return this._decodeInt(8, true); },
	readUInt8:	function (){ return this._decodeInt(8, false); },
	readInt16:	function (){ return this._decodeInt(16, true); },
	readUInt16:	function (){ return this._decodeInt(16, false); },
	readInt32:	function (){ return this._decodeInt(32, true); },
	readUInt32:	function (){ return this._decodeInt(32, false); },

	readFloat:	function (){ return this._decodeFloat(23, 8); },
	readDouble:	function (){ return this._decodeFloat(52, 11); },
	
	readChar:	function () { return this.readString(1); },
	readString: function (length) {
		this._checkSize(length * 8);
		var result = this._buffer.substr(this._pos, length);
		this._pos += length;
		return result;
	},

	seek: function (pos) {
		this._pos = pos;
		this._checkSize(0);
	},
	
	getPosition: function () {
		return this._pos;
	},
	
	getSize: function () {
		return this._buffer.length;
	},


	/* Private */
	
	_decodeFloat: function(precisionBits, exponentBits){
		var length = precisionBits + exponentBits + 1;
		var size = length >> 3;
		this._checkSize(length);

		var bias = Math.pow(2, exponentBits - 1) - 1;
		var signal = this._readBits(precisionBits + exponentBits, 1, size);
		var exponent = this._readBits(precisionBits, exponentBits, size);
		var significand = 0;
		var divisor = 2;
    // var curByte = length + (-precisionBits >> 3) - 1;
		var curByte = 0;
		do {
			var byteValue = this._readByte(++curByte, size);
			var startBit = precisionBits % 8 || 8;
			var mask = 1 << startBit;
			while (mask >>= 1) {
				if (byteValue & mask) {
					significand += 1 / divisor;
				}
				divisor *= 2;
			}
		} while (precisionBits -= startBit);

		this._pos += size;

		return exponent == (bias << 1) + 1 ? significand ? NaN : signal ? -Infinity : +Infinity
			: (1 + signal * -2) * (exponent || significand ? !exponent ? Math.pow(2, -bias + 1) * significand
			: Math.pow(2, exponent - bias) * (1 + significand) : 0);
	},

	_decodeInt: function(bits, signed){
		var x = this._readBits(0, bits, bits / 8), max = Math.pow(2, bits);
		var result = signed && x >= max / 2 ? x - max : x;

		this._pos += bits / 8;
		return result;
	},

	//shl fix: Henri Torgemane ~1996 (compressed by Jonas Raoni)
	_shl: function (a, b){
		for (++b; --b; a = ((a %= 0x7fffffff + 1) & 0x40000000) == 0x40000000 ? a * 2 : (a - 0x40000000) * 2 + 0x7fffffff + 1);
		return a;
	},
	
	_readByte: function (i, size) {
		return this._buffer.charCodeAt(this._pos + size - i - 1) & 0xff;
	},

	_readBits: function (start, length, size) {
		var offsetLeft = (start + length) % 8;
		var offsetRight = start % 8;
		var curByte = size - (start >> 3) - 1;
		var lastByte = size + (-(start + length) >> 3);
		var diff = curByte - lastByte;

		var sum = (this._readByte(curByte, size) >> offsetRight) & ((1 << (diff ? 8 - offsetRight : length)) - 1);

		if (diff && offsetLeft) {
			sum += (this._readByte(lastByte++, size) & ((1 << offsetLeft) - 1)) << (diff-- << 3) - offsetRight; 
		}

		while (diff) {
			sum += this._shl(this._readByte(lastByte++, size), (diff-- << 3) - offsetRight);
		}

		return sum;
	},

	_checkSize: function (neededBits) {
		if (!(this._pos + Math.ceil(neededBits / 8) < this._buffer.length)) {
			throw new Error("Index out of bound");
		}
	}
};