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- 06.01.2017
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random_int.php
001 <?php
002 /**
003 * Random_* Compatibility Library
004 * for using the new PHP 7 random_* API in PHP 5 projects
005 *
006 * The MIT License (MIT)
007 *
008 * Copyright (c) 2015 Paragon Initiative Enterprises
009 *
010 * Permission is hereby granted, free of charge, to any person obtaining a copy
011 * of this software and associated documentation files (the "Software"), to deal
012 * in the Software without restriction, including without limitation the rights
013 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
014 * copies of the Software, and to permit persons to whom the Software is
015 * furnished to do so, subject to the following conditions:
016 *
017 * The above copyright notice and this permission notice shall be included in
018 * all copies or substantial portions of the Software.
019 *
020 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
021 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
022 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
023 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
024 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
025 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
026 * SOFTWARE.
027 */
028
029 /**
030 * Fetch a random integer between $min and $max inclusive
031 *
032 * @param int $min
033 * @param int $max
034 *
035 * @throws Exception
036 *
037 * @return int
038 */
039 function random_int($min, $max)
040 {
041 /**
042 * Type and input logic checks
043 *
044 * If you pass it a float in the range (~PHP_INT_MAX, PHP_INT_MAX)
045 * (non-inclusive), it will sanely cast it to an int. If you it's equal to
046 * ~PHP_INT_MAX or PHP_INT_MAX, we let it fail as not an integer. Floats
047 * lose precision, so the <= and => operators might accidentally let a float
048 * through.
049 */
050
051 try {
052 $min = RandomCompat_intval($min);
053 } catch (TypeError $ex) {
054 throw new TypeError(
055 'random_int(): $min must be an integer'
056 );
057 }
058
059 try {
060 $max = RandomCompat_intval($max);
061 } catch (TypeError $ex) {
062 throw new TypeError(
063 'random_int(): $max must be an integer'
064 );
065 }
066
067 /**
068 * Now that we've verified our weak typing system has given us an integer,
069 * let's validate the logic then we can move forward with generating random
070 * integers along a given range.
071 */
072 if ($min > $max) {
073 throw new Error(
074 'Minimum value must be less than or equal to the maximum value'
075 );
076 }
077
078 if ($max === $min) {
079 return $min;
080 }
081
082 /**
083 * Initialize variables to 0
084 *
085 * We want to store:
086 * $bytes => the number of random bytes we need
087 * $mask => an integer bitmask (for use with the &) operator
088 * so we can minimize the number of discards
089 */
090 $attempts = $bits = $bytes = $mask = $valueShift = 0;
091
092 /**
093 * At this point, $range is a positive number greater than 0. It might
094 * overflow, however, if $max - $min > PHP_INT_MAX. PHP will cast it to
095 * a float and we will lose some precision.
096 */
097 $range = $max - $min;
098
099 /**
100 * Test for integer overflow:
101 */
102 if (!is_int($range)) {
103
104 /**
105 * Still safely calculate wider ranges.
106 * Provided by @CodesInChaos, @oittaa
107 *
108 * @ref https://gist.github.com/CodesInChaos/03f9ea0b58e8b2b8d435
109 *
110 * We use ~0 as a mask in this case because it generates all 1s
111 *
112 * @ref https://eval.in/400356 (32-bit)
113 * @ref http://3v4l.org/XX9r5 (64-bit)
114 */
115 $bytes = PHP_INT_SIZE;
116 $mask = ~0;
117
118 } else {
119
120 /**
121 * $bits is effectively ceil(log($range, 2)) without dealing with
122 * type juggling
123 */
124 while ($range > 0) {
125 if ($bits % 8 === 0) {
126 ++$bytes;
127 }
128 ++$bits;
129 $range >>= 1;
130 $mask = $mask << 1 | 1;
131 }
132 $valueShift = $min;
133 }
134
135 /**
136 * Now that we have our parameters set up, let's begin generating
137 * random integers until one falls between $min and $max
138 */
139 do {
140 /**
141 * The rejection probability is at most 0.5, so this corresponds
142 * to a failure probability of 2^-128 for a working RNG
143 */
144 if ($attempts > 128) {
145 throw new Exception(
146 'random_int: RNG is broken - too many rejections'
147 );
148 }
149
150 /**
151 * Let's grab the necessary number of random bytes
152 */
153 $randomByteString = random_bytes($bytes);
154 if ($randomByteString === false) {
155 throw new Exception(
156 'Random number generator failure'
157 );
158 }
159
160 /**
161 * Let's turn $randomByteString into an integer
162 *
163 * This uses bitwise operators (<< and |) to build an integer
164 * out of the values extracted from ord()
165 *
166 * Example: [9F] | [6D] | [32] | [0C] =>
167 * 159 + 27904 + 3276800 + 201326592 =>
168 * 204631455
169 */
170 $val = 0;
171 for ($i = 0; $i < $bytes; ++$i) {
172 $val |= ord($randomByteString[$i]) << ($i * 8);
173 }
174
175 /**
176 * Apply mask
177 */
178 $val &= $mask;
179 $val += $valueShift;
180
181 ++$attempts;
182 /**
183 * If $val overflows to a floating point number,
184 * ... or is larger than $max,
185 * ... or smaller than $min,
186 * then try again.
187 */
188 } while (!is_int($val) || $val > $max || $val < $min);
189
190 return (int) $val;
191 }
192