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   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 - 2018 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              /** @var int $min */
  55              $min = RandomCompat_intval($min);
  56          } catch (TypeError $ex) {
  57              throw new TypeError(
  58                  'random_int(): $min must be an integer'
  59              );
  60          }
  61  
  62          try {
  63              /** @var int $max */
  64              $max = RandomCompat_intval($max);
  65          } catch (TypeError $ex) {
  66              throw new TypeError(
  67                  'random_int(): $max must be an integer'
  68              );
  69          }
  70  
  71          /**
  72           * Now that we've verified our weak typing system has given us an integer,
  73           * let's validate the logic then we can move forward with generating random
  74           * integers along a given range.
  75           */
  76          if ($min > $max) {
  77              throw new Error(
  78                  'Minimum value must be less than or equal to the maximum value'
  79              );
  80          }
  81  
  82          if ($max === $min) {
  83              return (int) $min;
  84          }
  85  
  86          /**
  87           * Initialize variables to 0
  88           *
  89           * We want to store:
  90           * $bytes => the number of random bytes we need
  91           * $mask => an integer bitmask (for use with the &) operator
  92           *          so we can minimize the number of discards
  93           */
  94          $attempts = $bits = $bytes = $mask = $valueShift = 0;
  95          /** @var int $attempts */
  96          /** @var int $bits */
  97          /** @var int $bytes */
  98          /** @var int $mask */
  99          /** @var int $valueShift */
 100  
 101          /**
 102           * At this point, $range is a positive number greater than 0. It might
 103           * overflow, however, if $max - $min > PHP_INT_MAX. PHP will cast it to
 104           * a float and we will lose some precision.
 105           *
 106           * @var int|float $range
 107           */
 108          $range = $max - $min;
 109  
 110          /**
 111           * Test for integer overflow:
 112           */
 113          if (!is_int($range)) {
 114  
 115              /**
 116               * Still safely calculate wider ranges.
 117               * Provided by @CodesInChaos, @oittaa
 118               *
 119               * @ref https://gist.github.com/CodesInChaos/03f9ea0b58e8b2b8d435
 120               *
 121               * We use ~0 as a mask in this case because it generates all 1s
 122               *
 123               * @ref https://eval.in/400356 (32-bit)
 124               * @ref http://3v4l.org/XX9r5  (64-bit)
 125               */
 126              $bytes = PHP_INT_SIZE;
 127              /** @var int $mask */
 128              $mask = ~0;
 129  
 130          } else {
 131  
 132              /**
 133               * $bits is effectively ceil(log($range, 2)) without dealing with
 134               * type juggling
 135               */
 136              while ($range > 0) {
 137                  if ($bits % 8 === 0) {
 138                      ++$bytes;
 139                  }
 140                  ++$bits;
 141                  $range >>= 1;
 142                  /** @var int $mask */
 143                  $mask = $mask << 1 | 1;
 144              }
 145              $valueShift = $min;
 146          }
 147  
 148          /** @var int $val */
 149          $val = 0;
 150          /**
 151           * Now that we have our parameters set up, let's begin generating
 152           * random integers until one falls between $min and $max
 153           */
 154          /** @psalm-suppress RedundantCondition */
 155          do {
 156              /**
 157               * The rejection probability is at most 0.5, so this corresponds
 158               * to a failure probability of 2^-128 for a working RNG
 159               */
 160              if ($attempts > 128) {
 161                  throw new Exception(
 162                      'random_int: RNG is broken - too many rejections'
 163                  );
 164              }
 165  
 166              /**
 167               * Let's grab the necessary number of random bytes
 168               */
 169              $randomByteString = random_bytes($bytes);
 170  
 171              /**
 172               * Let's turn $randomByteString into an integer
 173               *
 174               * This uses bitwise operators (<< and |) to build an integer
 175               * out of the values extracted from ord()
 176               *
 177               * Example: [9F] | [6D] | [32] | [0C] =>
 178               *   159 + 27904 + 3276800 + 201326592 =>
 179               *   204631455
 180               */
 181              $val &= 0;
 182              for ($i = 0; $i < $bytes; ++$i) {
 183                  $val |= ord($randomByteString[$i]) << ($i * 8);
 184              }
 185              /** @var int $val */
 186  
 187              /**
 188               * Apply mask
 189               */
 190              $val &= $mask;
 191              $val += $valueShift;
 192  
 193              ++$attempts;
 194              /**
 195               * If $val overflows to a floating point number,
 196               * ... or is larger than $max,
 197               * ... or smaller than $min,
 198               * then try again.
 199               */
 200          } while (!is_int($val) || $val > $max || $val < $min);
 201  
 202          return (int) $val;
 203      }
 204  }