mt_rand
(PHP 4, PHP 5)
mt_rand — Generate a better random value
Description
$min
, int $max
)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
mt_getrandmax(). If you want a random number
between 5 and 15 (inclusive), for example, use mt_rand(5,
15).
Parameters
-
min -
Optional lowest value to be returned (default: 0)
-
max -
Optional highest value to be returned (default: mt_getrandmax())
Return Values
A random integer value between min (or 0)
and max (or mt_getrandmax(), inclusive),
or FALSE if max is less than min.
Changelog
| Version | Description |
|---|---|
| 5.3.4 |
Issues an E_WARNING and returns FALSE if
max < min.
|
| 4.2.0 | The random number generator is seeded automatically. |
Examples
Example #1 mt_rand() example
<?php
echo mt_rand() . "\n";
echo mt_rand() . "\n";
echo mt_rand(5, 15);
?>
The above example will output something similar to:
1604716014 1478613278 6
Notes
This function does not generate cryptographically secure values, and should not be used for cryptographic purposes. If you need a cryptographically secure value, consider using openssl_random_pseudo_bytes() instead.
The distribution of mt_rand() return values is biased
towards even numbers on 64-bit builds of PHP when
max is beyond 2^32.
See Also
- mt_srand() - Seed the better random number generator
- mt_getrandmax() - Show largest possible random value
- openssl_random_pseudo_bytes() - Generate a pseudo-random string of bytes
- rand() - Generate a random integer
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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/>";
}
?>