vendor/paragonie/random_compat/lib/random_int.php

   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             $min = RandomCompat_intval($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 }