/* -*- Mode: js; js-indent-level: 2; -*- */
|
/*
|
* Copyright 2011 Mozilla Foundation and contributors
|
* Licensed under the New BSD license. See LICENSE or:
|
* http://opensource.org/licenses/BSD-3-Clause
|
*
|
* Based on the Base 64 VLQ implementation in Closure Compiler:
|
* https://code.google.com/p/closure-compiler/source/browse/trunk/src/com/google/debugging/sourcemap/Base64VLQ.java
|
*
|
* Copyright 2011 The Closure Compiler Authors. All rights reserved.
|
* Redistribution and use in source and binary forms, with or without
|
* modification, are permitted provided that the following conditions are
|
* met:
|
*
|
* * Redistributions of source code must retain the above copyright
|
* notice, this list of conditions and the following disclaimer.
|
* * Redistributions in binary form must reproduce the above
|
* copyright notice, this list of conditions and the following
|
* disclaimer in the documentation and/or other materials provided
|
* with the distribution.
|
* * Neither the name of Google Inc. nor the names of its
|
* contributors may be used to endorse or promote products derived
|
* from this software without specific prior written permission.
|
*
|
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
|
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
|
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
|
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
|
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
|
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
|
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
|
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
*/
|
|
const base64 = require("./base64");
|
|
// A single base 64 digit can contain 6 bits of data. For the base 64 variable
|
// length quantities we use in the source map spec, the first bit is the sign,
|
// the next four bits are the actual value, and the 6th bit is the
|
// continuation bit. The continuation bit tells us whether there are more
|
// digits in this value following this digit.
|
//
|
// Continuation
|
// | Sign
|
// | |
|
// V V
|
// 101011
|
|
const VLQ_BASE_SHIFT = 5;
|
|
// binary: 100000
|
const VLQ_BASE = 1 << VLQ_BASE_SHIFT;
|
|
// binary: 011111
|
const VLQ_BASE_MASK = VLQ_BASE - 1;
|
|
// binary: 100000
|
const VLQ_CONTINUATION_BIT = VLQ_BASE;
|
|
/**
|
* Converts from a two-complement value to a value where the sign bit is
|
* placed in the least significant bit. For example, as decimals:
|
* 1 becomes 2 (10 binary), -1 becomes 3 (11 binary)
|
* 2 becomes 4 (100 binary), -2 becomes 5 (101 binary)
|
*/
|
function toVLQSigned(aValue) {
|
return aValue < 0
|
? ((-aValue) << 1) + 1
|
: (aValue << 1) + 0;
|
}
|
|
/**
|
* Converts to a two-complement value from a value where the sign bit is
|
* placed in the least significant bit. For example, as decimals:
|
* 2 (10 binary) becomes 1, 3 (11 binary) becomes -1
|
* 4 (100 binary) becomes 2, 5 (101 binary) becomes -2
|
*/
|
// eslint-disable-next-line no-unused-vars
|
function fromVLQSigned(aValue) {
|
const isNegative = (aValue & 1) === 1;
|
const shifted = aValue >> 1;
|
return isNegative
|
? -shifted
|
: shifted;
|
}
|
|
/**
|
* Returns the base 64 VLQ encoded value.
|
*/
|
exports.encode = function base64VLQ_encode(aValue) {
|
let encoded = "";
|
let digit;
|
|
let vlq = toVLQSigned(aValue);
|
|
do {
|
digit = vlq & VLQ_BASE_MASK;
|
vlq >>>= VLQ_BASE_SHIFT;
|
if (vlq > 0) {
|
// There are still more digits in this value, so we must make sure the
|
// continuation bit is marked.
|
digit |= VLQ_CONTINUATION_BIT;
|
}
|
encoded += base64.encode(digit);
|
} while (vlq > 0);
|
|
return encoded;
|
};
|
