/* -*- 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.
 */

var 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

var VLQ_BASE_SHIFT = 5;

// binary: 100000
var VLQ_BASE = 1 << VLQ_BASE_SHIFT;

// binary: 011111
var VLQ_BASE_MASK = VLQ_BASE - 1;

// binary: 100000
var 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
 */
function fromVLQSigned(aValue) {
  var isNegative = (aValue & 1) === 1;
  var shifted = aValue >> 1;
  return isNegative
    ? -shifted
    : shifted;
}

/**
 * Returns the base 64 VLQ encoded value.
 */
exports.encode = function base64VLQ_encode(aValue) {
  var encoded = "";
  var digit;

  var 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;
};

/**
 * Decodes the next base 64 VLQ value from the given string and returns the
 * value and the rest of the string via the out parameter.
 */
exports.decode = function base64VLQ_decode(aStr, aIndex, aOutParam) {
  var strLen = aStr.length;
  var result = 0;
  var shift = 0;
  var continuation, digit;

  do {
    if (aIndex >= strLen) {
      throw new Error("Expected more digits in base 64 VLQ value.");
    }

    digit = base64.decode(aStr.charCodeAt(aIndex++));
    if (digit === -1) {
      throw new Error("Invalid base64 digit: " + aStr.charAt(aIndex - 1));
    }

    continuation = !!(digit & VLQ_CONTINUATION_BIT);
    digit &= VLQ_BASE_MASK;
    result = result + (digit << shift);
    shift += VLQ_BASE_SHIFT;
  } while (continuation);

  aOutParam.value = fromVLQSigned(result);
  aOutParam.rest = aIndex;
};

.NET Framework

Project Request

ProjectC

Vehicle Maintenance

Movie Navigator

Customers Exchange

ATM

.NET Core

Mail Daemon

Custom

Buns of code

PHP

Mediabox

Loan Castle

Content Management

Laravel

Phone Check

Frontend

Forex Wall

Business projects

Certification Center

Amerikas Auto

Pet projects

Geolocation Assistant

Web Dynamics

Blackball

Good old times

DOS Clock

BrainOut

Airport Administrator

Atomizer

Mediabox