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<?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;
}
