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<title>Generate a better random value</title>
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<div class="refnamediv">
<h1 class="refname">mt_rand</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">mt_rand</span> — <span class="dc-title">Generate a better random value</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.mt-rand-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">int</span> <span class="methodname"><strong>mt_rand</strong></span>
( <span class="methodparam">void</span>
)</div>
<div class="methodsynopsis dc-description">
<span class="type">int</span> <span class="methodname"><strong>mt_rand</strong></span>
( <span class="methodparam"><span class="type">int</span> <code class="parameter">$min</code></span>
, <span class="methodparam"><span class="type">int</span> <code class="parameter">$max</code></span>
)</div>
<p class="simpara">
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 <span class="function"><a href="function.rand.html" class="function">rand()</a></span>
function. The <span class="function"><strong>mt_rand()</strong></span> function is a drop-in
replacement for this. It uses a random number generator with
known characteristics using the <a href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html" class="link external">»
Mersenne Twister</a>, which will produce random numbers four times
faster than what the average libc rand() provides.
</p>
<p class="simpara">
If called without the optional <em><code class="parameter">min</code></em>,
<em><code class="parameter">max</code></em> arguments <span class="function"><strong>mt_rand()</strong></span>
returns a pseudo-random value between 0 and
<span class="function"><a href="function.mt-getrandmax.html" class="function">mt_getrandmax()</a></span>. If you want a random number
between 5 and 15 (inclusive), for example, use <em>mt_rand(5,
15)</em>.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.mt-rand-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">min</code></em></span>
<dd>
<p class="para">
Optional lowest value to be returned (default: 0)
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">max</code></em></span>
<dd>
<p class="para">
Optional highest value to be returned (default: <span class="function"><a href="function.mt-getrandmax.html" class="function">mt_getrandmax()</a></span>)
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.mt-rand-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
A random integer value between <em><code class="parameter">min</code></em> (or 0)
and <em><code class="parameter">max</code></em> (or <span class="function"><a href="function.mt-getrandmax.html" class="function">mt_getrandmax()</a></span>, inclusive),
or <strong><code>FALSE</code></strong> if <em><code class="parameter">max</code></em> is less than <em><code class="parameter">min</code></em>.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.mt-rand-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.3.4</td>
<td>
Issues an <strong><code>E_WARNING</code></strong> and returns <strong><code>FALSE</code></strong> if
<em><code class="parameter">max</code></em> < <em><code class="parameter">min</code></em>.
</td>
</tr>
<tr><td>4.2.0</td><td>The random
number generator is seeded automatically.</td></tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.mt-rand-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-3467">
<p><strong>Example #1 <span class="function"><strong>mt_rand()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">() . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">() . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br />echo </span><span style="color: #0000BB">mt_rand</span><span style="color: #007700">(</span><span style="color: #0000BB">5</span><span style="color: #007700">, </span><span style="color: #0000BB">15</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output
something similar to:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
1604716014
1478613278
6
</pre></div>
</div>
</div>
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.mt-rand-notes">
<h3 class="title">Notes</h3>
<div class="caution"><strong class="caution">Caution</strong><p class="para">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 <span class="function"><a href="function.openssl-random-pseudo-bytes.html" class="function">openssl_random_pseudo_bytes()</a></span> instead.</p></div>
<div class="caution"><strong class="caution">Caution</strong>
<p class="para">
The distribution of <span class="function"><strong>mt_rand()</strong></span> return values is biased
towards even numbers on 64-bit builds of PHP when
<em><code class="parameter">max</code></em> is beyond <em>2^32</em>.
</p>
</div>
</div>
<div class="refsect1 seealso" id="refsect1-function.mt-rand-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.mt-srand.html" class="function" rel="rdfs-seeAlso">mt_srand()</a> - Seed the better random number generator</span></li>
<li class="member"> <span class="function"><a href="function.mt-getrandmax.html" class="function" rel="rdfs-seeAlso">mt_getrandmax()</a> - Show largest possible random value</span></li>
<li class="member"> <span class="function"><a href="function.openssl-random-pseudo-bytes.html" class="function" rel="rdfs-seeAlso">openssl_random_pseudo_bytes()</a> - Generate a pseudo-random string of bytes</span></li>
<li class="member"> <span class="function"><a href="function.rand.html" class="function" rel="rdfs-seeAlso">rand()</a> - Generate a random integer</span></li>
</ul>
</p>
</div>
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