calibre-web/cps/static/js/io/bitstream.js
2019-05-10 08:16:03 +09:00

289 lines
8.3 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 || {};
/**
* This object allows you to peek and consume bits and bytes out of a stream.
* Note that this stream is optimized, and thus, will *NOT* throw an error if
* the end of the stream is reached. Only use this in scenarios where you
* already have all the bits you need.
*/
bitjs.io.BitStream = class {
/**
* @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
*/
constructor(ab, rtl, opt_offset, opt_length) {
if (!(ab instanceof ArrayBuffer)) {
throw 'Error! BitArray constructed with an invalid ArrayBuffer object';
}
const offset = opt_offset || 0;
const length = opt_length || ab.byteLength;
/**
* The bytes in the stream.
* @type {Uint8Array}
* @private
*/
this.bytes = new Uint8Array(ab, offset, length);
/**
* The byte in the stream that we are currently on.
* @type {Number}
* @private
*/
this.bytePtr = 0;
/**
* The bit in the current byte that we will read next (can have values 0 through 7).
* @type {Number}
* @private
*/
this.bitPtr = 0; // tracks which bit we are on (can have values 0 through 7)
/**
* An ever-increasing number.
* @type {Number}
* @private
*/
this.bitsRead_ = 0;
this.peekBits = rtl ? this.peekBits_rtl : this.peekBits_ltr;
}
/**
* Returns how many bites have been read in the stream since the beginning of time.
*/
getNumBitsRead() {
return this.bitsRead_;
}
/**
* Returns how many bits are currently in the stream left to be read.
*/
getNumBitsLeft() {
const bitsLeftInByte = 8 - this.bitPtr;
return (this.bytes.byteLength - this.bytePtr - 1) * 8 + bitsLeftInByte;
}
/**
* 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, must be a positive integer.
* @param {boolean=} movePointers Whether to move the pointer, defaults false.
* @return {number} The peeked bits, as an unsigned number.
*/
peekBits_ltr(n, opt_movePointers) {
const NUM = parseInt(n, 10);
let num = NUM;
if (n !== num || num <= 0) {
return 0;
}
const BITMASK = bitjs.io.BitStream.BITMASK;
const movePointers = opt_movePointers || false;
let bytes = this.bytes;
let bytePtr = this.bytePtr;
let bitPtr = this.bitPtr;
let result = 0;
let bitsIn = 0;
// keep going until we have no more bits left to peek at
while (num > 0) {
// We overflowed the stream, so just return what we got.
if (bytePtr >= bytes.length) {
break;
}
const numBitsLeftInThisByte = (8 - bitPtr);
if (num >= numBitsLeftInThisByte) {
const mask = (BITMASK[numBitsLeftInThisByte] << bitPtr);
result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
bytePtr++;
bitPtr = 0;
bitsIn += numBitsLeftInThisByte;
num -= numBitsLeftInThisByte;
} else {
const mask = (BITMASK[num] << bitPtr);
result |= (((bytes[bytePtr] & mask) >> bitPtr) << bitsIn);
bitPtr += num;
break;
}
}
if (movePointers) {
this.bitPtr = bitPtr;
this.bytePtr = bytePtr;
this.bitsRead_ += NUM;
}
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. Must be a positive integer.
* @param {boolean=} movePointers Whether to move the pointer, defaults false.
* @return {number} The peeked bits, as an unsigned number.
*/
peekBits_rtl(n, opt_movePointers) {
const NUM = parseInt(n, 10);
let num = NUM;
if (n !== num || num <= 0) {
return 0;
}
const BITMASK = bitjs.io.BitStream.BITMASK;
const movePointers = opt_movePointers || false;
let bytes = this.bytes;
let bytePtr = this.bytePtr;
let bitPtr = this.bitPtr;
let result = 0;
// keep going until we have no more bits left to peek at
while (num > 0) {
// We overflowed the stream, so just return the bits we got.
if (bytePtr >= bytes.length) {
break;
}
const numBitsLeftInThisByte = (8 - bitPtr);
if (num >= numBitsLeftInThisByte) {
result <<= numBitsLeftInThisByte;
result |= (BITMASK[numBitsLeftInThisByte] & bytes[bytePtr]);
bytePtr++;
bitPtr = 0;
num -= numBitsLeftInThisByte;
} else {
result <<= num;
const numBits = 8 - num - bitPtr;
result |= ((bytes[bytePtr] & (BITMASK[num] << numBits)) >> numBits);
bitPtr += num;
break;
}
}
if (movePointers) {
this.bitPtr = bitPtr;
this.bytePtr = bytePtr;
this.bitsRead_ += NUM;
}
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.
*/
getBits() {
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. Must be a positive integer.
* @return {number} The read bits, as an unsigned number.
*/
readBits(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. Must be a positive integer.
* @param {boolean=} movePointers Whether to move the pointer, defaults false.
* @return {Uint8Array} The subarray.
*/
peekBytes(n, opt_movePointers) {
const num = parseInt(n, 10);
if (n !== num || num < 0) {
throw 'Error! Called peekBytes() with a non-positive integer: ' + n;
} else if (num === 0) {
return new Uint8Array();
}
// Flush bits until we are byte-aligned.
// 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);
}
const numBytesLeft = this.getNumBitsLeft() / 8;
if (num > numBytesLeft) {
throw 'Error! Overflowed the bit stream! n=' + num + ', bytePtr=' + this.bytePtr +
', bytes.length=' + this.bytes.length + ', bitPtr=' + this.bitPtr;
}
const movePointers = opt_movePointers || false;
const result = new Uint8Array(num);
let bytes = this.bytes;
let ptr = this.bytePtr;
let bytesLeftToCopy = num;
while (bytesLeftToCopy > 0) {
const bytesLeftInStream = bytes.length - ptr;
const sourceLength = Math.min(bytesLeftToCopy, bytesLeftInStream);
result.set(bytes.subarray(ptr, ptr + sourceLength), num - bytesLeftToCopy);
ptr += sourceLength;
// Overflowed the stream, just return what we got.
if (ptr >= bytes.length) {
break;
}
bytesLeftToCopy -= sourceLength;
}
if (movePointers) {
this.bytePtr += num;
this.bitsRead_ += (num * 8);
}
return result;
}
/**
* @param {number} n The number of bytes to read.
* @return {Uint8Array} The subarray.
*/
readBytes(n) {
return this.peekBytes(n, true);
}
}
// mask for getting N number of bits (0-8)
bitjs.io.BitStream.BITMASK = [0, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0xFF ];