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/wp-includes/random_compat/ -> random_int.php (source)

   1  <?php
   2  
   3  if (!is_callable('random_int')) {
   4      /**
   5       * Random_* Compatibility Library
   6       * for using the new PHP 7 random_* API in PHP 5 projects
   7       *
   8       * The MIT License (MIT)
   9       *
  10       * Copyright (c) 2015 - 2017 Paragon Initiative Enterprises
  11       *
  12       * Permission is hereby granted, free of charge, to any person obtaining a copy
  13       * of this software and associated documentation files (the "Software"), to deal
  14       * in the Software without restriction, including without limitation the rights
  15       * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  16       * copies of the Software, and to permit persons to whom the Software is
  17       * furnished to do so, subject to the following conditions:
  18       *
  19       * The above copyright notice and this permission notice shall be included in
  20       * all copies or substantial portions of the Software.
  21       *
  22       * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  23       * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  24       * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  25       * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  26       * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  27       * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  28       * SOFTWARE.
  29       */
  30  
  31      /**
  32       * Fetch a random integer between $min and $max inclusive
  33       *
  34       * @param int $min
  35       * @param int $max
  36       *
  37       * @throws Exception
  38       *
  39       * @return int
  40       */
  41      function random_int($min, $max)
  42      {
  43          /**
  44           * Type and input logic checks
  45           *
  46           * If you pass it a float in the range (~PHP_INT_MAX, PHP_INT_MAX)
  47           * (non-inclusive), it will sanely cast it to an int. If you it's equal to
  48           * ~PHP_INT_MAX or PHP_INT_MAX, we let it fail as not an integer. Floats
  49           * lose precision, so the <= and => operators might accidentally let a float
  50           * through.
  51           */
  52  
  53          try {
  54              $min = RandomCompat_intval($min);
  55          } catch (TypeError $ex) {
  56              throw new TypeError(
  57                  'random_int(): $min must be an integer'
  58              );
  59          }
  60  
  61          try {
  62              $max = RandomCompat_intval($max);
  63          } catch (TypeError $ex) {
  64              throw new TypeError(
  65                  'random_int(): $max must be an integer'
  66              );
  67          }
  68  
  69          /**
  70           * Now that we've verified our weak typing system has given us an integer,
  71           * let's validate the logic then we can move forward with generating random
  72           * integers along a given range.
  73           */
  74          if ($min > $max) {
  75              throw new Error(
  76                  'Minimum value must be less than or equal to the maximum value'
  77              );
  78          }
  79  
  80          if ($max === $min) {
  81              return (int) $min;
  82          }
  83  
  84          /**
  85           * Initialize variables to 0
  86           *
  87           * We want to store:
  88           * $bytes => the number of random bytes we need
  89           * $mask => an integer bitmask (for use with the &) operator
  90           *          so we can minimize the number of discards
  91           */
  92          $attempts = $bits = $bytes = $mask = $valueShift = 0;
  93  
  94          /**
  95           * At this point, $range is a positive number greater than 0. It might
  96           * overflow, however, if $max - $min > PHP_INT_MAX. PHP will cast it to
  97           * a float and we will lose some precision.
  98           */
  99          $range = $max - $min;
 100  
 101          /**
 102           * Test for integer overflow:
 103           */
 104          if (!is_int($range)) {
 105  
 106              /**
 107               * Still safely calculate wider ranges.
 108               * Provided by @CodesInChaos, @oittaa
 109               *
 110               * @ref https://gist.github.com/CodesInChaos/03f9ea0b58e8b2b8d435
 111               *
 112               * We use ~0 as a mask in this case because it generates all 1s
 113               *
 114               * @ref https://eval.in/400356 (32-bit)
 115               * @ref http://3v4l.org/XX9r5  (64-bit)
 116               */
 117              $bytes = PHP_INT_SIZE;
 118              $mask = ~0;
 119  
 120          } else {
 121  
 122              /**
 123               * $bits is effectively ceil(log($range, 2)) without dealing with
 124               * type juggling
 125               */
 126              while ($range > 0) {
 127                  if ($bits % 8 === 0) {
 128                      ++$bytes;
 129                  }
 130                  ++$bits;
 131                  $range >>= 1;
 132                  $mask = $mask << 1 | 1;
 133              }
 134              $valueShift = $min;
 135          }
 136  
 137          $val = 0;
 138          /**
 139           * Now that we have our parameters set up, let's begin generating
 140           * random integers until one falls between $min and $max
 141           */
 142          do {
 143              /**
 144               * The rejection probability is at most 0.5, so this corresponds
 145               * to a failure probability of 2^-128 for a working RNG
 146               */
 147              if ($attempts > 128) {
 148                  throw new Exception(
 149                      'random_int: RNG is broken - too many rejections'
 150                  );
 151              }
 152  
 153              /**
 154               * Let's grab the necessary number of random bytes
 155               */
 156              $randomByteString = random_bytes($bytes);
 157  
 158              /**
 159               * Let's turn $randomByteString into an integer
 160               *
 161               * This uses bitwise operators (<< and |) to build an integer
 162               * out of the values extracted from ord()
 163               *
 164               * Example: [9F] | [6D] | [32] | [0C] =>
 165               *   159 + 27904 + 3276800 + 201326592 =>
 166               *   204631455
 167               */
 168              $val &= 0;
 169              for ($i = 0; $i < $bytes; ++$i) {
 170                  $val |= ord($randomByteString[$i]) << ($i * 8);
 171              }
 172  
 173              /**
 174               * Apply mask
 175               */
 176              $val &= $mask;
 177              $val += $valueShift;
 178  
 179              ++$attempts;
 180              /**
 181               * If $val overflows to a floating point number,
 182               * ... or is larger than $max,
 183               * ... or smaller than $min,
 184               * then try again.
 185               */
 186          } while (!is_int($val) || $val > $max || $val < $min);
 187  
 188          return (int) $val;
 189      }
 190  }


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