mt_rand

(PHP 4, PHP 5, PHP 7, PHP 8)

mt_rand — 生成更好的随机数

说明

mt_rand ( ) : int
mt_rand ( int $min , int $max ) : int

很多老的 libc 的随机数发生器具有一些不确定和未知的特性而且很慢。PHP 的 rand() 函数默认使用 libc 随机数发生器。mt_rand() 函数是非正式用来替换它的。该函数用了 » Mersenne Twister 中已知的特性作为随机数发生器，它可以产生随机数值的平均速度比 libc 提供的 rand() 快四倍。

如果没有提供可选参数 min 和 max，mt_rand() 返回 0 到 mt_getrandmax() 之间的伪随机数。例如想要 5 到 15（包括 5 和 15）之间的随机数，用 mt_rand(5, 15)。

参数

min

可选的、返回的最小值（默认：0）

max

可选的、返回的最大值（默认：mt_getrandmax()）

返回值

返回 min （或者 0） 到 max （或者是到 mt_getrandmax() ，包含这个值）之间的随机整数。

更新日志

版本 说明
4.2.0随机数发生器自动进行播种。

范例

Example #1 mt_rand() 例子

<?php
echo mt_rand() . "\n";
echo mt_rand() . "\n";

echo mt_rand(5, 15);
?>

以上例程的输出类似于：

1604716014
1478613278
6

注释

Caution

The distribution of mt_rand() return values is biased towards even numbers on 64-bit builds of PHP when max is beyond 2^32.

参见

User Contributed Notes

Nikhil S. 03-Feb-2020 05:19
A nifty function to generate pretty coupon codes. This will generate unique coupon codes and you don't have to do a database check whether the code already exists.

<?php
function giftCodes(){
    $a='';
    for($j=0; $j<=4; $j++){
        $c = 4;
        if($j == 1) { $a .= date("d"); $c=2; }
        if($j == 3) { $a .= date("m"); $c=2; }
        if($j == 4) { $a .= date("y"); $c=2; }
        for($i=0; $i<= $c; $i++)
            $a .= chr(!mt_rand(0,2)?mt_rand(48,57):mt_rand(65,90));
        $a .='-';
    }
    return substr($a, 0, -1);
}
?>
Anonymous 20-Dec-2018 08:24
The seed is the PID + LCG (https://github.com/php/php-src/search?q=GENERATE_SEED&unscoped_q=GENERATE_SEED)
nospamremove dot francois dot gannaz at silecs dot info 03-Jun-2016 10:49
rand() comes from the libc, and mt_rand() is internal to PHP. So the differences vary with their respective versions.

On a 64b Debian Stretch with PHP 5.6.21, there is no visible difference: http://oi64.tinypic.com/2nkqas6.jpg

This image compares the two functions. In the top half with random points, in the lower half with random intensity on each point. This is totally different from what was obtained 4 years ago in another note, with an unknown environment.

Here is the code for this visual comparison.
<?php
$sizex = 400;
$sizey = 400;

$img = imagecreatetruecolor(2 * $sizex, 2 * $sizey);
$white = imagecolorallocate($img, 255, 255, 255);
$inks = array_map(
    function($r) use($img) { return imagecolorallocate($img, $r, $r, $r); },
    range(0, 255)
);
for ($x = 0 ; $x < $sizex ; $x++) {
    for ($y = 0 ; $y < $sizey ; $y++) {
        // placing ($sizex x $sizey) white points at random in the top half
        imagesetpixel($img, rand(0, $sizex - 1), rand(0, $sizey - 1), $white);
        imagesetpixel($img, $sizex + mt_rand(0, $sizex - 1), mt_rand(0, $sizey - 1), $white);
        // random intensity for each point in the lower half
        imagesetpixel($img, $x, $sizey + $y, $inks[rand(0, 255)]);
        imagesetpixel($img, $sizex + $x, $sizey + $y, $inks[mt_rand(0, 255)]);
    }
}
header("Content-type: image/png");
imagepng($img);
?>
syouseki 19-Feb-2016 05:18
mt_rand is not calculated by Mersenne Twister.

https://github.com/php/php-src/commit/a0724d30817600540946b41e40f4cfc2a0c30f80
Jeff Cours 12-Sep-2014 10:12
With PHP 5.3.3, we're seeing odd behavior on 32 bit Linux.

This works fine on 64 bit Linux:
<?php
printf ("%08x\n", mt_rand (0, 0xFFFFFFFF));
?>
but on our 32 bit Linux development server, it's always yielding "00000000".

On that same machine, this:
<?php
printf ("%08x\n", mt_rand (0, 0xFFFFFFF0));
?>
seems to always yield either 00000000 or a number in the range fffffff2 to ffffffff. This:
<?php
printf ("%08x\n", mt_rand (0, 0xFFFFFF00));
?>
gives numbers where the last two digits vary, and so on through at least 0xF0000000.

However, this:
<?php
printf ("%08x\n", mt_rand (0, 0x7FFFFFFF));
?>
seems to be well-behaved.

The moral? On 32 bit systems, be careful about crossing the signed number boundary, 0x7FFFFFFF.
falkartis at gmail dot com 12-Jul-2014 03:34
I wrote another function to get a random float, if its not precise enougth jut add some '0' to the $mul parameter.

<?php

function f_rand($min=0,$max=1,$mul=1000000){
    if ($min>$max) return false;
    return mt_rand($min*$mul,$max*$mul)/$mul;
}
?>
I made following  tests:
<?php
    echo f_rand()."<br>";              //0.497153
    echo f_rand(0.5)."<br>";           //0.857822
    echo f_rand(0.5,0.6)."<br>";       //0.599956
    echo f_rand(0,10)."<br>";          //5.801949
    echo f_rand(0,2,2)."<br>";         //1.5
    echo f_rand(0,2,10)."<br>";        //1.7
?>
Pawe Krawczyk 05-Nov-2013 11:13
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
Miller 02-Aug-2013 06:05
Another generic random string function, but very small and fast.

<?php
function mt_rand_str ($l, $c = 'abcdefghijklmnopqrstuvwxyz1234567890') {
    for ($s = '', $cl = strlen($c)-1, $i = 0; $i < $l; $s .= $c[mt_rand(0, $cl)], ++$i);
    return $s;
}

echo mt_rand_str(8); // Something like mp2tmpsw
echo mt_rand_str(6, '0123456789ABCDEF'); // Something like B9CD0F
?>
Hayley Watson 29-Jan-2013 10:56
Another graphical comparison of rand() and mt_rand(). It effectively draws a graph showing how the last generated number affects the next by plotting the numbers in consecutive pairs against each other.

<?php
header("Content-type: image/png");
$sizex=800;
$sizey=800;

$img = imagecreatetruecolor(2 * $sizex,$sizey);
$black = imagecolorallocate($img,0, 0, 0);
imagefilledrectangle($img, 0, 0, 2 * $sizex, $sizey, imagecolorallocate($img, 255, 255, 255));

$p = 0;
for($i=0; $i < 100000; $i++) {
    $np = rand(0,$sizex);
    imagesetpixel($img, $p, $np, $black);
    $p = $np;
}

$p = 0;
for($i=0; $i < 100000; $i++) {
    $np = mt_rand(0,$sizex);
    imagesetpixel($img, $p + $sizex, $np, $black);
    $p = $np;
}

imagepng($img);
imagedestroy($img);
?>
cyrax21 at gmail dot com 01-Mar-2012 08:44
i wanted to spot out the big difference between rand and mt_rand when producing images using randomness as noise.

for example this is a comparation between rand and mt_rand on a 400x400 pixel png: http://oi43.tinypic.com/vwtppl.jpg

code:
<?php
header("Content-type: image/png");
$sizex=800;
$sizey=400;

$img = imagecreatetruecolor($sizex,$sizey);
$ink = imagecolorallocate($img,255,255,255);

for($i=0;$i<$sizex/2;$i++) {
  for($j=0;$j<$sizey;$j++) {
  imagesetpixel($img, rand(1,$sizex/2), rand(1,$sizey), $ink);
  }
}
 
for($i=$sizex/2;$i<$sizex;$i++) {
  for($j=0;$j<$sizey;$j++) {
  imagesetpixel($img, mt_rand($sizex/2,$sizex), mt_rand(1,$sizey), $ink);
  }
}

imagepng($img);
imagedestroy($img);
?>

the differences reduce when reducing the pixels of the image.. infact for a 100x100 pixel image the noise produced from the rand function is much more realistic than how it is for a 400x400 image: http://oi39.tinypic.com/5k0row.jpg

(rand is on the left, mt_rand on the right)
contact at sheyd dot fr 24-Nov-2011 04:43
To quickly build a human-readable random string for a captcha per example :

<?php

function random($length = 8)
{     
    $chars = 'bcdfghjklmnprstvwxzaeiou';
   
    for ($p = 0; $p < $length; $p++)
    {
        $result .= ($p%2) ? $chars[mt_rand(19, 23)] : $chars[mt_rand(0, 18)];
    }
   
    return $result;
}

?>

Note that I have removed q and y from $chars to avoid readability problems.
j dot s dot shiuan at gmail dot com 02-Sep-2011 11:12
Another good way to get a random float is to divide the result of mt_rand.
Let's say we want a float between 0.75 and 1.25.

<?php

$i = mt_rand(75,125) / 100;

?>
Robin Leffmann 25-Dec-2010 06:14
Fast, pseudo-random binary data generation using mt_rand():

<?php

function rnd_bin( $length )
{
    while( @$c++ * 16 < $length )
        @$tmp .= md5( mt_rand(), true );
    return substr( $tmp, 0, $length );
}

?>
nilesh at itech7 dot com 19-May-2010 12:20
A class to generate 99.5% unqiue strings. I found that there is only one or two characters common between two subsequent strings.

<?php

class Local_RandomString {
 
  protected $_length;
  protected $_prevRand;

  public function __construct($length = 15) {
   
    $this->_length = $length;

  }

  public function getRand() {
   
    $randStr = null;   
    $args[] = 'N' . $this->_length;

    for($i = 0; $i < $this->_length; $i++) {
      $args[] = mt_rand();     
    }
   
    $randStr = substr(base64_encode((call_user_func_array('pack', $args))), 1, $this->_length);
    $this->_prevRand = $randStr;
    return $randStr;

  }

  public function setLength($l) {
   
    $this->_length = (int) $l;
   
    if($this->_length <= 0) {
      throw new Exception('Invalid random string length');
    }

  }

  public function getPrevRand() {
   
    return $this->_prevRand;

  }

}
?>
mark omohundro, ajamyajax dot com 19-Feb-2009 09:13
just another example: both of these routines return a random decimal number between -1 and 1... since rand() only returns a max 'integer' value while mt_rand() return a max 'long' value -- at least on some platforms -- mt_rand() could be the better precision choice for some on any variation to this routine (but i don't think it matters here):

<?php
echo "-1 to 1 rand() value: ". (rand(getrandmax()*-1,getrandmax())/getrandmax()). "\n<br/>";
echo "-1 to 1 mt_rand() value: ". (mt_rand(mt_getrandmax()*-1,mt_getrandmax())/mt_getrandmax()). "\n";
?>
Mark Seecof 05-Jun-2008 11:31
If you need some pseudorandom bits for security or cryptographic purposes (e.g.g., random IV for block cipher, random salt for password hash) mt_rand() is a poor source.  On most Unix/Linux and/or MS-Windows platforms you can get a better grade of pseudorandom bits from the OS or system library, like this:

<?php
// get 128 pseudorandom bits in a string of 16 bytes

$pr_bits = '';

// Unix/Linux platform?
$fp = @fopen('/dev/urandom','rb');
if ($fp !== FALSE) {
    $pr_bits .= @fread($fp,16);
    @fclose($fp);
}

// MS-Windows platform?
if (@class_exists('COM')) {
    // http://msdn.microsoft.com/en-us/library/aa388176(VS.85).aspx
    try {
        $CAPI_Util = new COM('CAPICOM.Utilities.1');
        $pr_bits .= $CAPI_Util->GetRandom(16,0);

        // if we ask for binary data PHP munges it, so we
        // request base64 return value.  We squeeze out the
        // redundancy and useless ==CRLF by hashing...
        if ($pr_bits) { $pr_bits = md5($pr_bits,TRUE); }
    } catch (Exception $ex) {
        // echo 'Exception: ' . $ex->getMessage();
    }
}

if (strlen($pr_bits) < 16) {
    // do something to warn system owner that
    // pseudorandom generator is missing
}
?>

NB: it is generally safe to leave both the attempt to read /dev/urandom and the attempt to access CAPICOM in your code, though each will fail silently on the other's platform.  Leave them both there so your code will be more portable.
geompse at yopmail dot com 29-Mar-2008 04:01
mt_rand() is not faster than rand() !

Tested over 100'000 iterations, with none/various/random arguments, mt_rand is always 3% slower than rand().
fabiovh on gmail 13-Nov-2007 06:42
performance: for a repetitive task, it's much faster not to use the limit parameters, as shown below. just use the % operator.

$t=microtime(true);
for($i=0;$i<1000000;$i++)
 mt_rand()%3;
echo microtime(true)-$t;

echo '|';

$t=microtime(true);
for($i=0;$i<1000000;$i++)
 mt_rand(0,2);
echo microtime(true)-$t;

echo '|';

$t=microtime(true);
for($i=0;$i<1000000;$i++)
 mt_rand();
echo microtime(true)-$t;

output: 0.316797971725|0.442242145538|0.253082036972
rok dot kralj at gmail dot com 16-Jun-2007 12:42
mt_rand function returns just a whole numbers. If you want a random float, then here's an elegant way:

<?php
function random_float ($min,$max) {
   return ($min+lcg_value()*(abs($max-$min)));
}
?>
chagenbu at php dot net 21-Mar-2007 09:18
The algorithm used by mt_rand() changed in PHP 5.2.1. If you are relying on getting the same sequence from mt_rand() after calling mt_srand() with a known seed, upgrading to PHP 5.2.1 will break your code. See http://bugs.php.net/bug.php?id=40724 for something of an explanation; there is no workaround.
zolaar at nothanks dot com 07-Feb-2007 10:44
a better (and likely faster) way to generate a random 6-digit hex string:

<?php
$num = mt_rand ( 0, 0xffffff ); // trust the library, love the library...
$output = sprintf ( "%06x" , $num ); // muchas smoochas to you, PHP!
return $output;
?>

The mt_rand function won't give you a number outside the bounds you asked for -- no need to and-off the top bits -- and the sprintf function has params for length-padding & hexidecimal output.  It's likely faster because most of the work is being done by the wicked fast C functions that PHP sits on top of, though YMMV in that dept.
nowhere at where dot net 16-Apr-2005 02:46
Allows characters 0-9, a-z
Weighted (and tested) ok.

<?php
function generate_string ($length = 20)
{
    $nps = "";
    for($i=0;$i<$length;$i++)
    {
        $nps .= chr( (mt_rand(1, 36) <= 26) ? mt_rand(97, 122) : mt_rand(48, 57 ));
    }
    return $nps;
}
?>
11-Feb-2004 05:27
Here is a example of a very small, compact, quite random-random string generator. It will make a string with uppercase & lowercase letters, with numbers. You simply need to set $len in the for() structure, and then the string will be in $r.  It has been designed for size, while it's still quite fast.  Mind the wrapping, it should be 1 line.

<?php
for($len=8,$r='';strlen($r)<$len;$r.=chr(!mt_rand(0,2)?
mt_rand(48,57):(!mt_rand(0,1)?mt_rand(65,90):mt_rand
(97,122))));
?>

Armond Carroll
demogracia at metropoliglobal dot com 02-Mar-2002 12:38
<?php
//
// Generates a random string with the specified length
// Chars are chosen from the provided [optional] list
//
function simpleRandString($length=16, $list="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"){
    mt_srand((double)microtime()*1000000);
    $newstring="";

    if($length>0){
        while(strlen($newstring)<$length){
            $newstring.=$list[mt_rand(0, strlen($list)-1)];
        }
    }
    return $newstring;
}

//
// Generates a random string with the specified length
// Includes: a-z, A-Z y 0-9
//
function randString($length=16) {
   $newstring="";
   if($length>0) {
       while(strlen($newstring)<$length) {
           $randnum = mt_rand(0,61);
           if ($randnum < 10) {
               $newstring.=chr($randnum+48);
           } elseif ($randnum < 36) {
               $newstring.=chr($randnum+55);
           } else {
               $newstring.=chr($randnum+61);
           }
       }
   }
   return $newstring;
}
?>