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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 328689 $ -->
<refentry xml:id="function.mt-rand" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<refnamediv>
<refname>mt_rand</refname>
<refpurpose>Generate a better random value</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>int</type><methodname>mt_rand</methodname>
<void/>
</methodsynopsis>
<methodsynopsis>
<type>int</type><methodname>mt_rand</methodname>
<methodparam><type>int</type><parameter>min</parameter></methodparam>
<methodparam><type>int</type><parameter>max</parameter></methodparam>
</methodsynopsis>
<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 <function>rand</function>
function. The <function>mt_rand</function> function is a drop-in
replacement for this. It uses a random number generator with
known characteristics using the <link xlink:href="&url.mersenne;">
Mersenne Twister</link>, which will produce random numbers four times
faster than what the average libc rand() provides.
</simpara>
<simpara>
If called without the optional <parameter>min</parameter>,
<parameter>max</parameter> arguments <function>mt_rand</function>
returns a pseudo-random value between 0 and
<function>mt_getrandmax</function>. If you want a random number
between 5 and 15 (inclusive), for example, use <literal>mt_rand(5,
15)</literal>.
</simpara>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>min</parameter></term>
<listitem>
<para>
Optional lowest value to be returned (default: 0)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>max</parameter></term>
<listitem>
<para>
Optional highest value to be returned (default: <function>mt_getrandmax</function>)
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
A random integer value between <parameter>min</parameter> (or 0)
and <parameter>max</parameter> (or <function>mt_getrandmax</function>, inclusive),
or &false; if <parameter>max</parameter> is less than <parameter>min</parameter>.
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>5.3.4</entry>
<entry>
Issues an <constant>E_WARNING</constant> and returns &false; if
<parameter>max</parameter> < <parameter>min</parameter>.
</entry>
</row>
&changelog.randomseed;
</tbody>
</tgroup>
</informaltable>
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>mt_rand</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
echo mt_rand() . "\n";
echo mt_rand() . "\n";
echo mt_rand(5, 15);
?>
]]>
</programlisting>
&example.outputs.similar;
<screen>
<![CDATA[
1604716014
1478613278
6
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
&caution.cryptographically-insecure;
<caution>
<para>
The distribution of <function>mt_rand</function> return values is biased
towards even numbers on 64-bit builds of PHP when
<parameter>max</parameter> is beyond <literal>2^32</literal>.
</para>
</caution>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>mt_srand</function></member>
<member><function>mt_getrandmax</function></member>
<member><function>openssl_random_pseudo_bytes</function></member>
<member><function>rand</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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