[Summary view]

Differences Between: [Versions 310 and 401] [Versions 311 and 401] [Versions 39 and 401]

   1  <?php
   2  
   3  /**
   4   * SCSSPHP
   5   *
   6   * @copyright 2012-2020 Leaf Corcoran
   7   *
   8   * @license http://opensource.org/licenses/MIT MIT
   9   *
  10   * @link http://scssphp.github.io/scssphp
  11   */
  12  
  13  namespace ScssPhp\ScssPhp\SourceMap;
  14  
  15  /**
  16   * Base 64 VLQ
  17   *
  18   * Based on the Base 64 VLQ implementation in Closure Compiler:
  19   * https://github.com/google/closure-compiler/blob/master/src/com/google/debugging/sourcemap/Base64VLQ.java
  20   *
  21   * Copyright 2011 The Closure Compiler Authors.
  22   *
  23   * Licensed under the Apache License, Version 2.0 (the "License");
  24   * you may not use this file except in compliance with the License.
  25   * You may obtain a copy of the License at
  26   *
  27   *     http://www.apache.org/licenses/LICENSE-2.0
  28   *
  29   * Unless required by applicable law or agreed to in writing, software
  30   * distributed under the License is distributed on an "AS IS" BASIS,
  31   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  32   * See the License for the specific language governing permissions and
  33   * limitations under the License.
  34   *
  35   * @author John Lenz <johnlenz@google.com>
  36   * @author Anthon Pang <anthon.pang@gmail.com>
  37   *
  38   * @internal
  39   */
  40  class Base64VLQ
  41  {
  42      // A Base64 VLQ digit can represent 5 bits, so it is base-32.
  43      const VLQ_BASE_SHIFT = 5;
  44  
  45      // A mask of bits for a VLQ digit (11111), 31 decimal.
  46      const VLQ_BASE_MASK = 31;
  47  
  48      // The continuation bit is the 6th bit.
  49      const VLQ_CONTINUATION_BIT = 32;
  50  
  51      /**
  52       * Returns the VLQ encoded value.
  53       *
  54       * @param int $value
  55       *
  56       * @return string
  57       */
  58      public static function encode($value)
  59      {
  60          $encoded = '';
  61          $vlq = self::toVLQSigned($value);
  62  
  63          do {
  64              $digit = $vlq & self::VLQ_BASE_MASK;
  65  
  66              //$vlq >>>= self::VLQ_BASE_SHIFT; // unsigned right shift
  67              $vlq = (($vlq >> 1) & PHP_INT_MAX) >> (self::VLQ_BASE_SHIFT - 1);
  68  
  69              if ($vlq > 0) {
  70                  $digit |= self::VLQ_CONTINUATION_BIT;
  71              }
  72  
  73              $encoded .= Base64::encode($digit);
  74          } while ($vlq > 0);
  75  
  76          return $encoded;
  77      }
  78  
  79      /**
  80       * Decodes VLQValue.
  81       *
  82       * @param string $str
  83       * @param int    $index
  84       *
  85       * @return int
  86       */
  87      public static function decode($str, &$index)
  88      {
  89          $result = 0;
  90          $shift = 0;
  91  
  92          do {
  93              $c = $str[$index++];
  94              $digit = Base64::decode($c);
  95              $continuation = ($digit & self::VLQ_CONTINUATION_BIT) != 0;
  96              $digit &= self::VLQ_BASE_MASK;
  97              $result = $result + ($digit << $shift);
  98              $shift = $shift + self::VLQ_BASE_SHIFT;
  99          } while ($continuation);
 100  
 101          return self::fromVLQSigned($result);
 102      }
 103  
 104      /**
 105       * Converts from a two-complement value to a value where the sign bit is
 106       * is placed in the least significant bit.  For example, as decimals:
 107       *   1 becomes 2 (10 binary), -1 becomes 3 (11 binary)
 108       *   2 becomes 4 (100 binary), -2 becomes 5 (101 binary)
 109       *
 110       * @param int $value
 111       *
 112       * @return int
 113       */
 114      private static function toVLQSigned($value)
 115      {
 116          if ($value < 0) {
 117              return ((-$value) << 1) + 1;
 118          }
 119  
 120          return ($value << 1) + 0;
 121      }
 122  
 123      /**
 124       * Converts to a two-complement value from a value where the sign bit is
 125       * is placed in the least significant bit.  For example, as decimals:
 126       *   2 (10 binary) becomes 1, 3 (11 binary) becomes -1
 127       *   4 (100 binary) becomes 2, 5 (101 binary) becomes -2
 128       *
 129       * @param int $value
 130       *
 131       * @return int
 132       */
 133      private static function fromVLQSigned($value)
 134      {
 135          $negate = ($value & 1) === 1;
 136  
 137          //$value >>>= 1; // unsigned right shift
 138          $value = ($value >> 1) & PHP_INT_MAX;
 139  
 140          if (! $negate) {
 141              return $value;
 142          }
 143  
 144          // We need to OR 0x80000000 here to ensure the 32nd bit (the sign bit) is
 145          // always set for negative numbers. If `value` were 1, (meaning `negate` is
 146          // true and all other bits were zeros), `value` would now be 0. -0 is just
 147          // 0, and doesn't flip the 32nd bit as intended. All positive numbers will
 148          // successfully flip the 32nd bit without issue, so it's a noop for them.
 149          return -$value | 0x80000000;
 150      }
 151  }