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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<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 random value via the Mersenne Twister Random Number Generator</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.
The <function>mt_rand</function> function is a drop-in replacement
for the older <function>rand</function>. 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>
&caution.cryptographically-insecure;
</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).
</para>
</refsect1>
<refsect1 role="errors">
&reftitle.errors;
<itemizedlist>
<listitem>
<simpara>
If <parameter>max</parameter> is less than <parameter>min</parameter>, a
<classname>ValueError</classname> will be thrown.
</simpara>
</listitem>
</itemizedlist>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>8.0.0</entry>
<entry>
A <classname>ValueError</classname> will be thrown if <parameter>max</parameter> is less than <parameter>min</parameter>;
previously an <constant>E_WARNING</constant> was raised, and the function returned &false;.
</entry>
</row>
<row>
<entry>7.2.0</entry>
<entry>
<function>mt_rand</function> <link linkend="migration72.incompatible.rand-mt_rand-output">has received a bug fix</link> for a modulo bias bug. This means that sequences generated with a specific seed may differ from PHP 7.1 on 64-bit machines.
</entry>
</row>
<row>
<entry>7.1.0</entry>
<entry>
<function>rand</function> <link linkend="migration71.incompatible.rand-srand-aliases">has been made</link> an alias of <function>mt_rand</function>.
</entry>
</row>
<row>
<entry>7.1.0</entry>
<entry>
<function>mt_rand</function> <link linkend="migration71.incompatible.fixes-to-mt_rand-algorithm">has been updated</link> to use the fixed, correct, version of
the Mersenne Twister algorithm. To fall back to the old behaviour, use <function>mt_srand</function> with <constant>MT_RAND_PHP</constant> as the second parameter.
</entry>
</row>
</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), "\n";
?>
]]>
</programlisting>
&example.outputs.similar;
<screen>
<![CDATA[
1604716014
1478613278
6
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
<warning>
<para>
<parameter>min</parameter> <parameter>max</parameter> range must
be within the range <function>mt_getrandmax</function>. i.e. (<parameter>max</parameter> -
<parameter>min</parameter>) <= <function>mt_getrandmax</function>
Otherwise, <function>mt_rand</function> may return poorer random numbers
than it should.
</para>
</warning>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>mt_srand</function></member>
<member><function>mt_getrandmax</function></member>
<member><function>random_int</function></member>
<member><function>random_bytes</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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