mt_rand
(PHP 4, PHP 5)
mt_rand — Generate a better random value
Описание
Many random number generators of older libcs have dubious or unknown characteristics and are slow. By default, PHP uses the libc random number generator with the rand() function. The mt_rand() function is a drop-in replacement for this. It uses a random number generator with known characteristics using the » Mersenne Twister, which will produce random numbers four times faster than what the average libc rand() provides.
If called without the optional min , max arguments mt_rand() returns a pseudo-random value between 0 and RAND_MAX. If you want a random number between 5 and 15 (inclusive), for example, use mt_rand (5, 15).
Замечание: Начиная с PHP 4.2.0, больше нет необходимости инициализировать генератор случайных чисел функциями srand() или mt_srand(), поскольку теперь это происходит автоматически.
Список параметров
- min
-
Optional lowest value to be returned (default: 0)
- max
-
Optional highest value to be returned (default: RAND_MAX)
Возвращаемые значения
A random integer value between min (or 0) and max (or RAND_MAX, inclusive)
Список изменений
| Версия | Описание |
|---|---|
| Since 3.0.7 | In versions before 3.0.7 the meaning of max was range . To get the same results in these versions the short example should be rand (5, 11) to get a random number between 5 and 15. |
Примеры
Пример #1 mt_rand() example
<?php
echo mt_rand() . "\n";
echo mt_rand() . "\n";
echo mt_rand(5, 15);
?>
Результатом выполнения данного примера будет что-то подобное:
1604716014 1478613278 6
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Коментарии
To reiterate the message about *not* using mt_rand() for anything security related, here's a new tool that has been just posted that recovers the seed value given a single mt_rand() output:
http://www.openwall.com/php_mt_seed/README
The seed is the PID + LCG (https://github.com/php/php-src/search?q=GENERATE_SEED&unscoped_q=GENERATE_SEED)To see some systematic deviations from a universal distribution run:
<?php
$alfabet = str_split('ADHKLMNPSTUWX');
$countalfabet = count($alfabet)-1;
$code = array_fill_keys($alfabet, 0);
for ($L=0; $L<80*$countalfabet; $L++)
{
$lettr = floor(mt_rand ( 0, $countalfabet ));
$code[$alfabet[$lettr]]++;
}
foreach($code as $L => $Freq)
{
for($F=0; $F<$Freq; $F++)
{
echo $L;
}
echo "\n<br/>";
}
?>