2a09d1a4
 liuqimichale
添加宜春 天水 宣化
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'use strict';
var ExpGolomb;
/**
* Parser for exponential Golomb codes, a variable-bitwidth number encoding
* scheme used by h264.
*/
ExpGolomb = function(workingData) {
var
// the number of bytes left to examine in workingData
workingBytesAvailable = workingData.byteLength,
// the current word being examined
workingWord = 0, // :uint
// the number of bits left to examine in the current word
workingBitsAvailable = 0; // :uint;
// ():uint
this.length = function() {
return (8 * workingBytesAvailable);
};
// ():uint
this.bitsAvailable = function() {
return (8 * workingBytesAvailable) + workingBitsAvailable;
};
// ():void
this.loadWord = function() {
var
position = workingData.byteLength - workingBytesAvailable,
workingBytes = new Uint8Array(4),
availableBytes = Math.min(4, workingBytesAvailable);
if (availableBytes === 0) {
throw new Error('no bytes available');
}
workingBytes.set(workingData.subarray(position,
position + availableBytes));
workingWord = new DataView(workingBytes.buffer).getUint32(0);
// track the amount of workingData that has been processed
workingBitsAvailable = availableBytes * 8;
workingBytesAvailable -= availableBytes;
};
// (count:int):void
this.skipBits = function(count) {
var skipBytes; // :int
if (workingBitsAvailable > count) {
workingWord <<= count;
workingBitsAvailable -= count;
} else {
count -= workingBitsAvailable;
skipBytes = Math.floor(count / 8);
count -= (skipBytes * 8);
workingBytesAvailable -= skipBytes;
this.loadWord();
workingWord <<= count;
workingBitsAvailable -= count;
}
};
// (size:int):uint
this.readBits = function(size) {
var
bits = Math.min(workingBitsAvailable, size), // :uint
valu = workingWord >>> (32 - bits); // :uint
// if size > 31, handle error
workingBitsAvailable -= bits;
if (workingBitsAvailable > 0) {
workingWord <<= bits;
} else if (workingBytesAvailable > 0) {
this.loadWord();
}
bits = size - bits;
if (bits > 0) {
return valu << bits | this.readBits(bits);
}
return valu;
};
// ():uint
this.skipLeadingZeros = function() {
var leadingZeroCount; // :uint
for (leadingZeroCount = 0; leadingZeroCount < workingBitsAvailable; ++leadingZeroCount) {
if ((workingWord & (0x80000000 >>> leadingZeroCount)) !== 0) {
// the first bit of working word is 1
workingWord <<= leadingZeroCount;
workingBitsAvailable -= leadingZeroCount;
return leadingZeroCount;
}
}
// we exhausted workingWord and still have not found a 1
this.loadWord();
return leadingZeroCount + this.skipLeadingZeros();
};
// ():void
this.skipUnsignedExpGolomb = function() {
this.skipBits(1 + this.skipLeadingZeros());
};
// ():void
this.skipExpGolomb = function() {
this.skipBits(1 + this.skipLeadingZeros());
};
// ():uint
this.readUnsignedExpGolomb = function() {
var clz = this.skipLeadingZeros(); // :uint
return this.readBits(clz + 1) - 1;
};
// ():int
this.readExpGolomb = function() {
var valu = this.readUnsignedExpGolomb(); // :int
if (0x01 & valu) {
// the number is odd if the low order bit is set
return (1 + valu) >>> 1; // add 1 to make it even, and divide by 2
}
return -1 * (valu >>> 1); // divide by two then make it negative
};
// Some convenience functions
// :Boolean
this.readBoolean = function() {
return this.readBits(1) === 1;
};
// ():int
this.readUnsignedByte = function() {
return this.readBits(8);
};
this.loadWord();
};
module.exports = ExpGolomb;
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