92 lines
2.6 KiB
JavaScript
92 lines
2.6 KiB
JavaScript
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/**
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* Copyright (c) 2016-present, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*
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* @providesModule utf8
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* @flow
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*/
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'use strict';
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class ByteVector {
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_storage: Uint8Array;
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_sizeWritten: number;
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constructor(size) {
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this._storage = new Uint8Array(size);
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this._sizeWritten = 0;
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}
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push(value: number): ByteVector {
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const i = this._sizeWritten;
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if (i === this._storage.length) {
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this._realloc();
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}
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this._storage[i] = value;
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this._sizeWritten = i + 1;
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return this;
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}
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getBuffer(): ArrayBuffer {
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return this._storage.buffer.slice(0, this._sizeWritten);
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}
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_realloc() {
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const storage = this._storage;
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this._storage = new Uint8Array(align(storage.length * 1.5));
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this._storage.set(storage);
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}
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}
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/*eslint-disable no-bitwise */
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exports.encode = (string: string): ArrayBuffer => {
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const {length} = string;
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const bytes = new ByteVector(length);
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// each character / char code is assumed to represent an UTF-16 wchar.
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// With the notable exception of surrogate pairs, each wchar represents the
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// corresponding unicode code point.
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// For an explanation of UTF-8 encoding, read [1]
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// For an explanation of UTF-16 surrogate pairs, read [2]
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//
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// [1] https://en.wikipedia.org/wiki/UTF-8#Description
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// [2] https://en.wikipedia.org/wiki/UTF-16#U.2B10000_to_U.2B10FFFF
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let nextCodePoint = string.charCodeAt(0);
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for (let i = 0; i < length; i++) {
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let codePoint = nextCodePoint;
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nextCodePoint = string.charCodeAt(i + 1);
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if (codePoint < 0x80) {
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bytes.push(codePoint);
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} else if (codePoint < 0x800) {
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bytes
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.push(0xc0 | codePoint >>> 6)
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.push(0x80 | codePoint & 0x3f);
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} else if (codePoint >>> 10 === 0x36 && nextCodePoint >>> 10 === 0x37) { // high surrogate & low surrogate
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codePoint = 0x10000 + (((codePoint & 0x3ff) << 10) | (nextCodePoint & 0x3ff));
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bytes
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.push(0xf0 | codePoint >>> 18 & 0x7)
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.push(0x80 | codePoint >>> 12 & 0x3f)
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.push(0x80 | codePoint >>> 6 & 0x3f)
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.push(0x80 | codePoint & 0x3f);
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i += 1;
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nextCodePoint = string.charCodeAt(i + 1);
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} else {
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bytes
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.push(0xe0 | codePoint >>> 12)
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.push(0x80 | codePoint >>> 6 & 0x3f)
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.push(0x80 | codePoint & 0x3f);
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}
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}
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return bytes.getBuffer();
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};
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// align to multiples of 8 bytes
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function align(size: number): number {
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return size % 8 ? (Math.floor(size / 8) + 1) << 3 : size;
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}
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