mirror of
https://github.com/janeczku/calibre-web
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167 lines
4.7 KiB
JavaScript
167 lines
4.7 KiB
JavaScript
/*
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* bytestream.js
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*
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* Provides readers for byte streams.
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*
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* Licensed under the MIT License
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*
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* Copyright(c) 2011 Google Inc.
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* Copyright(c) 2011 antimatter15
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*/
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/* global bitjs, Uint8Array */
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var bitjs = bitjs || {};
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bitjs.io = bitjs.io || {};
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(function() {
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/**
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* This object allows you to peek and consume bytes as numbers and strings
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* out of an ArrayBuffer. In this buffer, everything must be byte-aligned.
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*
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* @param {ArrayBuffer} ab The ArrayBuffer object.
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* @param {number=} optOffset The offset into the ArrayBuffer
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* @param {number=} optLength The length of this BitStream
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* @constructor
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*/
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bitjs.io.ByteStream = function(ab, optOffset, optLength) {
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var offset = optOffset || 0;
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var length = optLength || ab.byteLength;
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this.bytes = new Uint8Array(ab, offset, length);
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this.ptr = 0;
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};
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/**
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* Peeks at the next n bytes as an unsigned number but does not advance the
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* pointer
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* TODO: This apparently cannot read more than 4 bytes as a number?
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* @param {number} n The number of bytes to peek at.
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* @return {number} The n bytes interpreted as an unsigned number.
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*/
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bitjs.io.ByteStream.prototype.peekNumber = function(n) {
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// TODO: return error if n would go past the end of the stream?
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if (n <= 0 || typeof n !== typeof 1) {
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return -1;
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}
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var result = 0;
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// read from last byte to first byte and roll them in
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var curByte = this.ptr + n - 1;
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while (curByte >= this.ptr) {
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result <<= 8;
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result |= this.bytes[curByte];
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--curByte;
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}
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return result;
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};
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/**
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* Returns the next n bytes as an unsigned number (or -1 on error)
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* and advances the stream pointer n bytes.
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* @param {number} n The number of bytes to read.
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* @return {number} The n bytes interpreted as an unsigned number.
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*/
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bitjs.io.ByteStream.prototype.readNumber = function(n) {
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var num = this.peekNumber(n);
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this.ptr += n;
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return num;
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};
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/**
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* Returns the next n bytes as a signed number but does not advance the
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* pointer.
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* @param {number} n The number of bytes to read.
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* @return {number} The bytes interpreted as a signed number.
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*/
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bitjs.io.ByteStream.prototype.peekSignedNumber = function(n) {
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var num = this.peekNumber(n);
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var HALF = Math.pow(2, (n * 8) - 1);
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var FULL = HALF * 2;
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if (num >= HALF) num -= FULL;
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return num;
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};
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/**
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* Returns the next n bytes as a signed number and advances the stream pointer.
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* @param {number} n The number of bytes to read.
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* @return {number} The bytes interpreted as a signed number.
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*/
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bitjs.io.ByteStream.prototype.readSignedNumber = function(n) {
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var num = this.peekSignedNumber(n);
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this.ptr += n;
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return num;
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};
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/**
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* This returns n bytes as a sub-array, advancing the pointer if movePointers
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* is true.
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* @param {number} n The number of bytes to read.
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* @param {boolean} movePointers Whether to move the pointers.
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* @return {Uint8Array} The subarray.
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*/
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bitjs.io.ByteStream.prototype.peekBytes = function(n, movePointers) {
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if (n <= 0 || typeof n !== typeof 1) {
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return null;
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}
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var result = this.bytes.subarray(this.ptr, this.ptr + n);
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if (movePointers) {
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this.ptr += n;
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}
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return result;
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};
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/**
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* Reads the next n bytes as a sub-array.
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* @param {number} n The number of bytes to read.
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* @return {Uint8Array} The subarray.
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*/
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bitjs.io.ByteStream.prototype.readBytes = function(n) {
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return this.peekBytes(n, true);
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};
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/**
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* Peeks at the next n bytes as a string but does not advance the pointer.
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* @param {number} n The number of bytes to peek at.
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* @return {string} The next n bytes as a string.
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*/
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bitjs.io.ByteStream.prototype.peekString = function(n) {
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if (n <= 0 || typeof n !== typeof 1) {
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return "";
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}
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var result = "";
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for (var p = this.ptr, end = this.ptr + n; p < end; ++p) {
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result += String.fromCharCode(this.bytes[p]);
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}
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return result;
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};
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/**
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* Returns the next n bytes as an ASCII string and advances the stream pointer
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* n bytes.
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* @param {number} n The number of bytes to read.
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* @return {string} The next n bytes as a string.
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*/
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bitjs.io.ByteStream.prototype.readString = function(n) {
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var strToReturn = this.peekString(n);
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this.ptr += n;
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return strToReturn;
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};
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})();
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