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parallel-library/cps/static/js/bytestream.js

309 lines
8.3 KiB
JavaScript

/*
* bytestream.js
*
* Provides readers for byte streams.
*
* 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 bytes as numbers and strings out
* of a stream. More bytes can be pushed into the back of the stream via the
* push() method.
*/
bitjs.io.ByteStream = class {
/**
* @param {ArrayBuffer} ab The ArrayBuffer object.
* @param {number=} opt_offset The offset into the ArrayBuffer
* @param {number=} opt_length The length of this BitStream
*/
constructor(ab, 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 current page of bytes in the stream.
* @type {Uint8Array}
* @private
*/
this.bytes = new Uint8Array(ab, offset, length);
/**
* The next pages of bytes in the stream.
* @type {Array<Uint8Array>}
* @private
*/
this.pages_ = [];
/**
* The byte in the current page that we will read next.
* @type {Number}
* @private
*/
this.ptr = 0;
/**
* An ever-increasing number.
* @type {Number}
* @private
*/
this.bytesRead_ = 0;
}
/**
* Returns how many bytes have been read in the stream since the beginning of time.
*/
getNumBytesRead() {
return this.bytesRead_;
}
/**
* Returns how many bytes are currently in the stream left to be read.
*/
getNumBytesLeft() {
const bytesInCurrentPage = (this.bytes.byteLength - this.ptr);
return this.pages_.reduce((acc, arr) => acc + arr.length, bytesInCurrentPage);
}
/**
* Move the pointer ahead n bytes. If the pointer is at the end of the current array
* of bytes and we have another page of bytes, point at the new page. This is a private
* method, no validation is done.
* @param {number} n Number of bytes to increment.
* @private
*/
movePointer_(n) {
this.ptr += n;
this.bytesRead_ += n;
while (this.ptr >= this.bytes.length && this.pages_.length > 0) {
this.ptr -= this.bytes.length;
this.bytes = this.pages_.shift();
}
}
/**
* Peeks at the next n bytes as an unsigned number but does not advance the
* pointer.
* @param {number} n The number of bytes to peek at. Must be a positive integer.
* @return {number} The n bytes interpreted as an unsigned number.
*/
peekNumber(n) {
const num = parseInt(n, 10);
if (n !== num || num < 0) {
throw 'Error! Called peekNumber() with a non-positive integer';
} else if (num === 0) {
return 0;
}
if (n > 4) {
throw 'Error! Called peekNumber(' + n +
') but this method can only reliably read numbers up to 4 bytes long';
}
if (this.getNumBytesLeft() < num) {
throw 'Error! Overflowed the byte stream while peekNumber()! n=' + num +
', ptr=' + this.ptr + ', bytes.length=' + this.getNumBytesLeft();
}
let result = 0;
let curPage = this.bytes;
let pageIndex = 0;
let ptr = this.ptr;
for (let i = 0; i < num; ++i) {
result |= (curPage[ptr++] << (i * 8));
if (ptr >= curPage.length) {
curPage = this.pages_[pageIndex++];
ptr = 0;
}
}
return result;
}
/**
* Returns the next n bytes as an unsigned number (or -1 on error)
* and advances the stream pointer n bytes.
* @param {number} n The number of bytes to read. Must be a positive integer.
* @return {number} The n bytes interpreted as an unsigned number.
*/
readNumber(n) {
const num = this.peekNumber(n);
this.movePointer_(n);
return num;
}
/**
* Returns the next n bytes as a signed number but does not advance the
* pointer.
* @param {number} n The number of bytes to read. Must be a positive integer.
* @return {number} The bytes interpreted as a signed number.
*/
peekSignedNumber(n) {
let num = this.peekNumber(n);
const HALF = Math.pow(2, (n * 8) - 1);
const FULL = HALF * 2;
if (num >= HALF) num -= FULL;
return num;
}
/**
* Returns the next n bytes as a signed number and advances the stream pointer.
* @param {number} n The number of bytes to read. Must be a positive integer.
* @return {number} The bytes interpreted as a signed number.
*/
readSignedNumber(n) {
const num = this.peekSignedNumber(n);
this.movePointer_(n);
return num;
}
/**
* This returns n bytes as a sub-array, advancing the pointer if movePointers
* is true.
* @param {number} n The number of bytes to read. Must be a positive integer.
* @param {boolean} movePointers Whether to move the pointers.
* @return {Uint8Array} The subarray.
*/
peekBytes(n, movePointers) {
const num = parseInt(n, 10);
if (n !== num || num < 0) {
throw 'Error! Called peekBytes() with a non-positive integer';
} else if (num === 0) {
return new Uint8Array();
}
const totalBytesLeft = this.getNumBytesLeft();
if (num > totalBytesLeft) {
throw 'Error! Overflowed the byte stream during peekBytes! n=' + num +
', ptr=' + this.ptr + ', bytes.length=' + this.getNumBytesLeft();
}
const result = new Uint8Array(num);
let curPage = this.bytes;
let ptr = this.ptr;
let bytesLeftToCopy = num;
let pageIndex = 0;
while (bytesLeftToCopy > 0) {
const bytesLeftInPage = curPage.length - ptr;
const sourceLength = Math.min(bytesLeftToCopy, bytesLeftInPage);
result.set(curPage.subarray(ptr, ptr + sourceLength), num - bytesLeftToCopy);
ptr += sourceLength;
if (ptr >= curPage.length) {
curPage = this.pages_[pageIndex++];
ptr = 0;
}
bytesLeftToCopy -= sourceLength;
}
if (movePointers) {
this.movePointer_(num);
}
return result;
}
/**
* Reads the next n bytes as a sub-array.
* @param {number} n The number of bytes to read. Must be a positive integer.
* @return {Uint8Array} The subarray.
*/
readBytes(n) {
return this.peekBytes(n, true);
}
/**
* Peeks at the next n bytes as an ASCII string but does not advance the pointer.
* @param {number} n The number of bytes to peek at. Must be a positive integer.
* @return {string} The next n bytes as a string.
*/
peekString(n) {
const num = parseInt(n, 10);
if (n !== num || num < 0) {
throw 'Error! Called peekString() with a non-positive integer';
} else if (num === 0) {
return '';
}
const totalBytesLeft = this.getNumBytesLeft();
if (num > totalBytesLeft) {
throw 'Error! Overflowed the byte stream while peekString()! n=' + num +
', ptr=' + this.ptr + ', bytes.length=' + this.getNumBytesLeft();
}
let result = new Array(num);
let curPage = this.bytes;
let pageIndex = 0;
let ptr = this.ptr;
for (let i = 0; i < num; ++i) {
result[i] = String.fromCharCode(curPage[ptr++]);
if (ptr >= curPage.length) {
curPage = this.pages_[pageIndex++];
ptr = 0;
}
}
return result.join('');
}
/**
* Returns the next n bytes as an ASCII string and advances the stream pointer
* n bytes.
* @param {number} n The number of bytes to read. Must be a positive integer.
* @return {string} The next n bytes as a string.
*/
readString(n) {
const strToReturn = this.peekString(n);
this.movePointer_(n);
return strToReturn;
}
/**
* Feeds more bytes into the back of the stream.
* @param {ArrayBuffer} ab
*/
push(ab) {
if (!(ab instanceof ArrayBuffer)) {
throw 'Error! ByteStream.push() called with an invalid ArrayBuffer object';
}
this.pages_.push(new Uint8Array(ab));
// If the pointer is at the end of the current page of bytes, this will advance
// to the next page.
this.movePointer_(0);
}
/**
* Creates a new ByteStream from this ByteStream that can be read / peeked.
* @return {bitjs.io.ByteStream} A clone of this ByteStream.
*/
tee() {
const clone = new bitjs.io.ByteStream(this.bytes.buffer);
clone.bytes = this.bytes;
clone.ptr = this.ptr;
clone.pages_ = this.pages_.slice();
clone.bytesRead_ = this.bytesRead_;
return clone;
}
}