118 lines
3 KiB
JavaScript
118 lines
3 KiB
JavaScript
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/*
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* bytestream.js
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*
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* Provides a writer for bytes.
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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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var bitjs = bitjs || {};
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bitjs.io = bitjs.io || {};
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/**
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* A write-only Byte buffer which uses a Uint8 Typed Array as a backing store.
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*/
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bitjs.io.ByteBuffer = class {
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/**
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* @param {number} numBytes The number of bytes to allocate.
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*/
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constructor(numBytes) {
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if (typeof numBytes != typeof 1 || numBytes <= 0) {
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throw "Error! ByteBuffer initialized with '" + numBytes + "'";
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}
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this.data = new Uint8Array(numBytes);
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this.ptr = 0;
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}
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/**
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* @param {number} b The byte to insert.
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*/
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insertByte(b) {
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// TODO: throw if byte is invalid?
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this.data[this.ptr++] = b;
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}
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/**
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* @param {Array.<number>|Uint8Array|Int8Array} bytes The bytes to insert.
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*/
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insertBytes(bytes) {
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// TODO: throw if bytes is invalid?
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this.data.set(bytes, this.ptr);
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this.ptr += bytes.length;
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}
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/**
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* Writes an unsigned number into the next n bytes. If the number is too large
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* to fit into n bytes or is negative, an error is thrown.
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* @param {number} num The unsigned number to write.
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* @param {number} numBytes The number of bytes to write the number into.
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*/
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writeNumber(num, numBytes) {
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if (numBytes < 1 || !numBytes) {
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throw 'Trying to write into too few bytes: ' + numBytes;
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}
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if (num < 0) {
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throw 'Trying to write a negative number (' + num +
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') as an unsigned number to an ArrayBuffer';
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}
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if (num > (Math.pow(2, numBytes * 8) - 1)) {
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throw 'Trying to write ' + num + ' into only ' + numBytes + ' bytes';
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}
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// Roll 8-bits at a time into an array of bytes.
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const bytes = [];
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while (numBytes-- > 0) {
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const eightBits = num & 255;
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bytes.push(eightBits);
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num >>= 8;
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}
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this.insertBytes(bytes);
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}
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/**
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* Writes a signed number into the next n bytes. If the number is too large
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* to fit into n bytes, an error is thrown.
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* @param {number} num The signed number to write.
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* @param {number} numBytes The number of bytes to write the number into.
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*/
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writeSignedNumber(num, numBytes) {
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if (numBytes < 1) {
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throw 'Trying to write into too few bytes: ' + numBytes;
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}
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const HALF = Math.pow(2, (numBytes * 8) - 1);
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if (num >= HALF || num < -HALF) {
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throw 'Trying to write ' + num + ' into only ' + numBytes + ' bytes';
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}
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// Roll 8-bits at a time into an array of bytes.
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const bytes = [];
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while (numBytes-- > 0) {
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const eightBits = num & 255;
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bytes.push(eightBits);
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num >>= 8;
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}
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this.insertBytes(bytes);
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}
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/**
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* @param {string} str The ASCII string to write.
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*/
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writeASCIIString(str) {
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for (let i = 0; i < str.length; ++i) {
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const curByte = str.charCodeAt(i);
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if (curByte < 0 || curByte > 255) {
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throw 'Trying to write a non-ASCII string!';
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}
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this.insertByte(curByte);
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}
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};
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}
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