123 lines
4.3 KiB
Plaintext
123 lines
4.3 KiB
Plaintext
/**
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* Portions Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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* @flow
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* @format
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* @oncall react_native
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*/
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/**
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* Copyright 2011 Mozilla Foundation and contributors
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* Licensed under the New BSD license. See LICENSE or:
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* http://opensource.org/licenses/BSD-3-Clause
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*
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* Based on the Base 64 VLQ implementation in Closure Compiler:
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* https://git.io/vymuA
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*
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* Copyright 2011 The Closure Compiler Authors. All rights reserved.
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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* * Neither the name of Google Inc. nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* @copyright
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*/
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/* eslint-disable no-bitwise */
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'use strict';
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// A map of values to characters for the b64 encoding
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const CHAR_MAP = [
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0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d,
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0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
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0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d,
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0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
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0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f,
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];
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// A single base 64 digit can contain 6 bits of data. For the base 64 variable
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// length quantities we use in the source map spec, the first bit is the sign,
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// the next four bits are the actual value, and the 6th bit is the
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// continuation bit. The continuation bit tells us whether there are more
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// digits in this value following this digit.
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//
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// Continuation
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// | Sign
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// | |
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// V V
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// 101011
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const VLQ_BASE_SHIFT = 5;
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// binary: 100000
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const VLQ_BASE = 1 << VLQ_BASE_SHIFT;
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// binary: 011111
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const VLQ_BASE_MASK = VLQ_BASE - 1;
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// binary: 100000
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const VLQ_CONTINUATION_BIT = VLQ_BASE;
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/**
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* Converts from a two-complement value to a value where the sign bit is
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* placed in the least significant bit. For example, as decimals:
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* 1 becomes 2 (10 binary), -1 becomes 3 (11 binary)
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* 2 becomes 4 (100 binary), -2 becomes 5 (101 binary)
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*/
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function toVLQSigned(value: number) {
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return value < 0 ? (-value << 1) + 1 : (value << 1) + 0;
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}
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/**
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* Encodes a number to base64 VLQ format and appends it to the passed-in buffer
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*
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* DON'T USE COMPOUND OPERATORS (eg `>>>=`) ON `let`-DECLARED VARIABLES!
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* V8 WILL DEOPTIMIZE THIS FUNCTION AND MAP CREATION WILL BE 25% SLOWER!
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*
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* DON'T ADD MORE COMMENTS TO THIS FUNCTION TO KEEP ITS LENGTH SHORT ENOUGH FOR
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* V8 OPTIMIZATION!
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*/
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function encode(value: number, buffer: Buffer, position: number): number {
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let vlq = toVLQSigned(value);
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let digit;
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do {
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digit = vlq & VLQ_BASE_MASK;
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vlq = vlq >>> VLQ_BASE_SHIFT;
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if (vlq > 0) {
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// There are still more digits in this value, so we must make sure the
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// continuation bit is marked.
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digit = digit | VLQ_CONTINUATION_BIT;
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}
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buffer[position++] = CHAR_MAP[digit];
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} while (vlq > 0);
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return position;
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}
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module.exports = encode;
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