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Diffstat (limited to '')
| -rw-r--r-- | include/random_compat/random_int.php | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/include/random_compat/random_int.php b/include/random_compat/random_int.php new file mode 100644 index 000000000..fd3ef87a2 --- /dev/null +++ b/include/random_compat/random_int.php @@ -0,0 +1,191 @@ +<?php +/** + * Random_* Compatibility Library + * for using the new PHP 7 random_* API in PHP 5 projects + * + * The MIT License (MIT) + * + * Copyright (c) 2015 Paragon Initiative Enterprises + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. + */ + +/** + * Fetch a random integer between $min and $max inclusive + * + * @param int $min + * @param int $max + * + * @throws Exception + * + * @return int + */ +function random_int($min, $max) +{ + /** + * Type and input logic checks + * + * If you pass it a float in the range (~PHP_INT_MAX, PHP_INT_MAX) + * (non-inclusive), it will sanely cast it to an int. If you it's equal to + * ~PHP_INT_MAX or PHP_INT_MAX, we let it fail as not an integer. Floats + * lose precision, so the <= and => operators might accidentally let a float + * through. + */ + + try { + $min = RandomCompat_intval($min); + } catch (TypeError $ex) { + throw new TypeError( + 'random_int(): $min must be an integer' + ); + } + + try { + $max = RandomCompat_intval($max); + } catch (TypeError $ex) { + throw new TypeError( + 'random_int(): $max must be an integer' + ); + } + + /** + * Now that we've verified our weak typing system has given us an integer, + * let's validate the logic then we can move forward with generating random + * integers along a given range. + */ + if ($min > $max) { + throw new Error( + 'Minimum value must be less than or equal to the maximum value' + ); + } + + if ($max === $min) { + return $min; + } + + /** + * Initialize variables to 0 + * + * We want to store: + * $bytes => the number of random bytes we need + * $mask => an integer bitmask (for use with the &) operator + * so we can minimize the number of discards + */ + $attempts = $bits = $bytes = $mask = $valueShift = 0; + + /** + * At this point, $range is a positive number greater than 0. It might + * overflow, however, if $max - $min > PHP_INT_MAX. PHP will cast it to + * a float and we will lose some precision. + */ + $range = $max - $min; + + /** + * Test for integer overflow: + */ + if (!is_int($range)) { + + /** + * Still safely calculate wider ranges. + * Provided by @CodesInChaos, @oittaa + * + * @ref https://gist.github.com/CodesInChaos/03f9ea0b58e8b2b8d435 + * + * We use ~0 as a mask in this case because it generates all 1s + * + * @ref https://eval.in/400356 (32-bit) + * @ref http://3v4l.org/XX9r5 (64-bit) + */ + $bytes = PHP_INT_SIZE; + $mask = ~0; + + } else { + + /** + * $bits is effectively ceil(log($range, 2)) without dealing with + * type juggling + */ + while ($range > 0) { + if ($bits % 8 === 0) { + ++$bytes; + } + ++$bits; + $range >>= 1; + $mask = $mask << 1 | 1; + } + $valueShift = $min; + } + + /** + * Now that we have our parameters set up, let's begin generating + * random integers until one falls between $min and $max + */ + do { + /** + * The rejection probability is at most 0.5, so this corresponds + * to a failure probability of 2^-128 for a working RNG + */ + if ($attempts > 128) { + throw new Exception( + 'random_int: RNG is broken - too many rejections' + ); + } + + /** + * Let's grab the necessary number of random bytes + */ + $randomByteString = random_bytes($bytes); + if ($randomByteString === false) { + throw new Exception( + 'Random number generator failure' + ); + } + + /** + * Let's turn $randomByteString into an integer + * + * This uses bitwise operators (<< and |) to build an integer + * out of the values extracted from ord() + * + * Example: [9F] | [6D] | [32] | [0C] => + * 159 + 27904 + 3276800 + 201326592 => + * 204631455 + */ + $val = 0; + for ($i = 0; $i < $bytes; ++$i) { + $val |= ord($randomByteString[$i]) << ($i * 8); + } + + /** + * Apply mask + */ + $val &= $mask; + $val += $valueShift; + + ++$attempts; + /** + * If $val overflows to a floating point number, + * ... or is larger than $max, + * ... or smaller than $min, + * then try again. + */ + } while (!is_int($val) || $val > $max || $val < $min); + + return (int) $val; +} |