125 lines
3.7 KiB
JavaScript
125 lines
3.7 KiB
JavaScript
// BinaryReader
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// Refactored by Vjeux <vjeuxx@gmail.com>
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// http://blog.vjeux.com/2010/javascript/javascript-binary-reader.html
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// Original
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// + Jonas Raoni Soares Silva
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// @ http://jsfromhell.com/classes/binary-deserializer [rev. #1]
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function BinaryReader (data) {
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this._buffer = data
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this._pos = 0
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}
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BinaryReader.prototype = {
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/* Public */
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readInt8: function () { return this._decodeInt(8, true) },
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readUInt8: function () { return this._decodeInt(8, false) },
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readInt16: function () { return this._decodeInt(16, true) },
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readUInt16: function () { return this._decodeInt(16, false) },
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readInt32: function () { return this._decodeInt(32, true) },
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readUInt32: function () { return this._decodeInt(32, false) },
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readFloat: function () { return this._decodeFloat(23, 8) },
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readDouble: function () { return this._decodeFloat(52, 11) },
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readChar: function () { return this.readString(1) },
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readString: function (length) {
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this._checkSize(length * 8)
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var result = this._buffer.substr(this._pos, length)
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this._pos += length
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return result
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},
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seek: function (pos) {
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this._pos = pos
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this._checkSize(0)
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},
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getPosition: function () {
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return this._pos
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},
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getSize: function () {
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return this._buffer.length
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},
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/* Private */
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_decodeFloat: function (precisionBits, exponentBits) {
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var length = precisionBits + exponentBits + 1
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var size = length >> 3
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this._checkSize(length)
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var bias = Math.pow(2, exponentBits - 1) - 1
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var signal = this._readBits(precisionBits + exponentBits, 1, size)
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var exponent = this._readBits(precisionBits, exponentBits, size)
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var significand = 0
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var divisor = 2
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var curByte = 0 // length + (-precisionBits >> 3) - 1;
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do {
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var byteValue = this._readByte(++curByte, size)
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var startBit = precisionBits % 8 || 8
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var mask = 1 << startBit
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while (mask >>= 1) {
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if (byteValue & mask) {
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significand += 1 / divisor
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}
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divisor *= 2
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}
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} while (precisionBits -= startBit)
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this._pos += size
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return exponent === (bias << 1) + 1 ? significand ? NaN : signal ? -Infinity : +Infinity
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: (1 + signal * -2) * (exponent || significand ? !exponent ? Math.pow(2, -bias + 1) * significand
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: Math.pow(2, exponent - bias) * (1 + significand) : 0)
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},
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_decodeInt: function (bits, signed) {
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var x = this._readBits(0, bits, bits / 8)
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var max = Math.pow(2, bits)
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var result = signed && x >= max / 2 ? x - max : x
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this._pos += bits / 8
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return result
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},
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// shl fix: Henri Torgemane ~1996 (compressed by Jonas Raoni)
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_shl: function (a, b) {
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for (++b; --b; a = ((a %= 0x7fffffff + 1) & 0x40000000) === 0x40000000 ? a * 2 : (a - 0x40000000) * 2 + 0x7fffffff + 1);
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return a
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},
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_readByte: function (i, size) {
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return this._buffer.charCodeAt(this._pos + size - i - 1) & 0xff
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},
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_readBits: function (start, length, size) {
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var offsetLeft = (start + length) % 8
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var offsetRight = start % 8
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var curByte = size - (start >> 3) - 1
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var lastByte = size + (-(start + length) >> 3)
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var diff = curByte - lastByte
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var sum = (this._readByte(curByte, size) >> offsetRight) & ((1 << (diff ? 8 - offsetRight : length)) - 1)
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if (diff && offsetLeft) {
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sum += (this._readByte(lastByte++, size) & ((1 << offsetLeft) - 1)) << (diff-- << 3) - offsetRight
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}
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while (diff) {
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sum += this._shl(this._readByte(lastByte++, size), (diff-- << 3) - offsetRight)
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}
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return sum
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},
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_checkSize: function (neededBits) {
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if (!(this._pos + Math.ceil(neededBits / 8) < this._buffer.length)) {
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// throw new Error("Index out of bound");
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}
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}
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}
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module.exports = BinaryReader
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