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    mt_rand

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

    mt_rand — Génère une valeur aléatoire via le générateur de nombre aléatoire Mersenne Twister

    Description

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

    Cette fonction ne génère pas de valeurs sécurisées d'un point de vue cryptographique, et ne doit pas être utilisée dans un contexte de chiffrement. Si vous avez besoin d'une valeur sécurisée d'un point de vue cryptographique, utilisez plutôt random_int(), random_bytes(), ou openssl_random_pseudo_bytes().

    De nombreux générateurs de nombres aléatoires provenant de vieilles bibliothèques libcs ont des comportements douteux et sont très lents. mt_rand() est une fonction de remplacement pour rand(). Elle utilise un générateur de nombres aléatoire de caractéristique connue, le " » Mersenne Twister " qui est 4 fois plus rapide que la fonction standard libc.

    Appelée sans les arguments optionnels min et max, mt_rand() retourne un nombre pseudoaléatoire, entre 0 et mt_getrandmax(). Pour obtenir un nombre entre 5 et 15 inclus, il faut utiliser mt_rand(5,15).

    Liste de paramètres

    min

    Valeur la plus basse qui peut être retournée (par défaut : 0)

    max

    Valeur la plus haute qui peut être retournée (par défaut : mt_getrandmax()).

    Valeurs de retour

    Un entier aléatoire compris entre min (ou 0) et max (ou mt_getrandmax(), inclusif), ou false si le paramètre max est inférieur à min.

    Historique

    Version Description
    7.2.0 mt_rand() a reçu une correction de bogue pour un bug de polarisation modulo. Cela signifie que les séquences générées avec une valeur d'initialisation spécifique peuvent différer de php 7.1 sur les machines 64-bit.
    7.1.0 rand() est devenu un alias de mt_rand().
    7.1.0 mt_rand() a été mis à jour pour utiliser la version corrigée, correcte, de l'algorithme Twister Mersenne. Pour revenir à l'ancien comportement, utilisez mt_srand() avec MT_RAND_PHP comme deuxième paramètre.

    Exemples

    Exemple #1 Exemple avec mt_rand()

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

    echo     mt_rand(5, 15);
    ?>

    Résultat de l'exemple ci-dessus est similaire à :

    1604716014
1478613278
6

    Notes

    Avertissement

    La plage min max doit se situer dans la plage mt_getrandmax(). i.e. max - min) <= mt_getrandmax() sinon, mt_rand() peut retourner des nombres aléatoires plus pauvres qu'il ne le devrait.

    Voir aussi

    • mt_srand() - Initialise le générateur de nombres aléatoires Mersenne Twister
    • mt_getrandmax() - La plus grande valeur aléatoire possible
    • random_int() - Génère des nombres entiers pseudo-aléatoire cryptographiquement sécurisé
    • random_bytes() - Génère des octets pseudo-aléatoire cryptographiquement sécurisé
    • openssl_random_pseudo_bytes() - Génère une chaine pseudo-aléatoire d'octets
    • rand() - Génère une valeur aléatoire

    add a note add a note

    User Contributed Notes 24 notes

    up
    101
    cyrax21 at gmail dot com
    12 years ago
    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)
    up
    13
    syouseki
    8 years ago
    mt_rand is not calculated by Mersenne Twister.

    https://github.com/php/php-src/commit/a0724d30817600540946b41e40f4cfc2a0c30f80
    up
    3
    Jeff Cours
    9 years ago
    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.
    up
    7
    zolaar at nothanks dot com
    17 years ago
    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.
    up
    4
    Hayley Watson
    11 years ago
    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);
    ?>
    up
    8
    contact at sheyd dot fr
    12 years ago
    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.
    up
    4
    falkartis at gmail dot com
    9 years ago
    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
    ?>
    up
    2
    Pawe Krawczyk
    10 years ago
    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
    up
    4
    chagenbu at php dot net
    17 years ago
    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.
    up
    4
    geompse at yopmail dot com
    16 years ago
    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().
    up
    5
    Miller
    10 years ago
    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
    ?>
    up
    3
    Mark Seecof
    15 years ago
    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.
    up
    1
    Anonymous
    20 years ago
    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
    up
    2
    mark omohundro, ajamyajax dot com
    15 years ago
    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";
    ?>
    up
    1
    demogracia at metropoliglobal dot com
    22 years ago
    <?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;
    }
    ?>
    up
    1
    nowhere at where dot net
    19 years ago
    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;
    }
    ?>
    up
    0
    Nikhil S.
    4 years ago
    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);
    }
    ?>
    up
    0
    Robin Leffmann
    13 years ago
    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 );
    }

    ?>
    up
    0
    rok dot kralj at gmail dot com
    16 years ago
    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)));
    }
    ?>
    up
    -1
    nospamremove dot francois dot gannaz at silecs dot info
    7 years ago
    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);
    ?>
    up
    -1
    nilesh at itech7 dot com
    13 years ago
    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;

      }

    }
    ?>
    up
    -2
    j dot s dot shiuan at gmail dot com
    12 years ago
    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;

    ?>
    up
    -3
    fabiovh on gmail
    16 years ago
    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
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