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parallel-library/cps/static/js/io/bitstream.js

233 lines
7.8 KiB
JavaScript

/*
* bitstream.js
*
* Provides readers for bitstreams.
*
* Licensed under the MIT License
*
* Copyright(c) 2011 Google Inc.
* Copyright(c) 2011 antimatter15
*/
var bitjs = bitjs || {};
bitjs.io = bitjs.io || {};
(function() {
// mask for getting the Nth bit (zero-based)
bitjs.BIT = [0x01, 0x02, 0x04, 0x08,
0x10, 0x20, 0x40, 0x80,
0x100, 0x200, 0x400, 0x800,
0x1000, 0x2000, 0x4000, 0x8000
];
// mask for getting N number of bits (0-8)
var BITMASK = [0, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0xFF];
/**
* This bit stream peeks and consumes bits out of a binary stream.
*
* @param {ArrayBuffer} ab An ArrayBuffer object or a Uint8Array.
* @param {boolean} rtl Whether the stream reads bits from the byte starting
* from bit 7 to 0 (true) or bit 0 to 7 (false).
* @param {Number} opt_offset The offset into the ArrayBuffer
* @param {Number} opt_length The length of this BitStream
*/
bitjs.io.BitStream = function(ab, rtl, opt_offset, opt_length) {
if (!ab || !ab.toString || ab.toString() !== "[object ArrayBuffer]") {
throw "Error! BitArray constructed with an invalid ArrayBuffer object";
}
var offset = opt_offset || 0;
var length = opt_length || ab.byteLength;
this.bytes = new Uint8Array(ab, offset, length);
this.bytePtr = 0; // tracks which byte we are on
this.bitPtr = 0; // tracks which bit we are on (can have values 0 through 7)
this.peekBits = rtl ? this.peekBits_rtl : this.peekBits_ltr;
};
/**
* byte0 byte1 byte2 byte3
* 7......0 | 7......0 | 7......0 | 7......0
*
* The bit pointer starts at bit0 of byte0 and moves left until it reaches
* bit7 of byte0, then jumps to bit0 of byte1, etc.
* @param {number} n The number of bits to peek.
* @param {boolean=} movePointers Whether to move the pointer, defaults false.
* @return {number} The peeked bits, as an unsigned number.
*/
bitjs.io.BitStream.prototype.peekBits_ltr = function(n, movePointers) {
if (n <= 0 || typeof n != typeof 1) {
return 0;
}
var movePointers = movePointers || false,
bytePtr = this.bytePtr,
bitPtr = this.bitPtr,
result = 0,
bitsIn = 0,
bytes = this.bytes;
// keep going until we have no more bits left to peek at
// TODO: Consider putting all bits from bytes we will need into a variable and then
// shifting/masking it to just extract the bits we want.
// This could be considerably faster when reading more than 3 or 4 bits at a time.
while (n > 0) {
if (bytePtr >= bytes.length) {
throw "Error! Overflowed the bit stream! n=" + n + ", bytePtr=" + bytePtr + ", bytes.length=" +
bytes.length + ", bitPtr=" + bitPtr;
return -1;
}
var numBitsLeftInThisByte = (8 - bitPtr);
if (n >= numBitsLeftInThisByte) {
var mask = (BITMASK[numBitsLeftInThisByte] << bitPtr);
result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
bytePtr++;
bitPtr = 0;
bitsIn += numBitsLeftInThisByte;
n -= numBitsLeftInThisByte;
} else {
var mask = (BITMASK[n] << bitPtr);
result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
bitPtr += n;
bitsIn += n;
n = 0;
}
}
if (movePointers) {
this.bitPtr = bitPtr;
this.bytePtr = bytePtr;
}
return result;
};
/**
* byte0 byte1 byte2 byte3
* 7......0 | 7......0 | 7......0 | 7......0
*
* The bit pointer starts at bit7 of byte0 and moves right until it reaches
* bit0 of byte0, then goes to bit7 of byte1, etc.
* @param {number} n The number of bits to peek.
* @param {boolean=} movePointers Whether to move the pointer, defaults false.
* @return {number} The peeked bits, as an unsigned number.
*/
bitjs.io.BitStream.prototype.peekBits_rtl = function(n, movePointers) {
if (n <= 0 || typeof n != typeof 1) {
return 0;
}
var movePointers = movePointers || false,
bytePtr = this.bytePtr,
bitPtr = this.bitPtr,
result = 0,
bytes = this.bytes;
// keep going until we have no more bits left to peek at
// TODO: Consider putting all bits from bytes we will need into a variable and then
// shifting/masking it to just extract the bits we want.
// This could be considerably faster when reading more than 3 or 4 bits at a time.
while (n > 0) {
if (bytePtr >= bytes.length) {
throw "Error! Overflowed the bit stream! n=" + n + ", bytePtr=" + bytePtr + ", bytes.length=" +
bytes.length + ", bitPtr=" + bitPtr;
return -1;
}
var numBitsLeftInThisByte = (8 - bitPtr);
if (n >= numBitsLeftInThisByte) {
result <<= numBitsLeftInThisByte;
result |= (BITMASK[numBitsLeftInThisByte] & bytes[bytePtr]);
bytePtr++;
bitPtr = 0;
n -= numBitsLeftInThisByte;
} else {
result <<= n;
result |= ((bytes[bytePtr] & (BITMASK[n] << (8 - n - bitPtr))) >> (8 - n - bitPtr));
bitPtr += n;
n = 0;
}
}
if (movePointers) {
this.bitPtr = bitPtr;
this.bytePtr = bytePtr;
}
return result;
};
/**
* Peek at 16 bits from current position in the buffer.
* Bit at (bytePtr,bitPtr) has the highest position in returning data.
* Taken from getbits.hpp in unrar.
* TODO: Move this out of BitStream and into unrar.
*/
bitjs.io.BitStream.prototype.getBits = function() {
return (((((this.bytes[this.bytePtr] & 0xff) << 16) +
((this.bytes[this.bytePtr + 1] & 0xff) << 8) +
((this.bytes[this.bytePtr + 2] & 0xff))) >>> (8 - this.bitPtr)) & 0xffff);
};
/**
* Reads n bits out of the stream, consuming them (moving the bit pointer).
* @param {number} n The number of bits to read.
* @return {number} The read bits, as an unsigned number.
*/
bitjs.io.BitStream.prototype.readBits = function(n) {
return this.peekBits(n, true);
};
/**
* This returns n bytes as a sub-array, advancing the pointer if movePointers
* is true. Only use this for uncompressed blocks as this throws away remaining
* bits in the current byte.
* @param {number} n The number of bytes to peek.
* @param {boolean=} movePointers Whether to move the pointer, defaults false.
* @return {Uint8Array} The subarray.
*/
bitjs.io.BitStream.prototype.peekBytes = function(n, movePointers) {
if (n <= 0 || typeof n != typeof 1) {
return 0;
}
// from http://tools.ietf.org/html/rfc1951#page-11
// "Any bits of input up to the next byte boundary are ignored."
while (this.bitPtr != 0) {
this.readBits(1);
}
var movePointers = movePointers || false;
var bytePtr = this.bytePtr,
bitPtr = this.bitPtr;
var result = this.bytes.subarray(bytePtr, bytePtr + n);
if (movePointers) {
this.bytePtr += n;
}
return result;
};
/**
* @param {number} n The number of bytes to read.
* @return {Uint8Array} The subarray.
*/
bitjs.io.BitStream.prototype.readBytes = function(n) {
return this.peekBytes(n, true);
};
})();