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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 297028 $ -->
<refentry xml:id="function.bcpowmod" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>bcpowmod</refname>
<refpurpose>Raise an arbitrary precision number to another, reduced by a specified modulus</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>string</type><methodname>bcpowmod</methodname>
<methodparam><type>string</type><parameter>left_operand</parameter></methodparam>
<methodparam><type>string</type><parameter>right_operand</parameter></methodparam>
<methodparam><type>string</type><parameter>modulus</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>scale</parameter></methodparam>
</methodsynopsis>
<para>
Use the fast-exponentiation method to raise
<parameter>left_operand</parameter> to the power
<parameter>right_operand</parameter> with respect to the modulus
<parameter>modulus</parameter>.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>left_operand</parameter></term>
<listitem>
<para>
The left operand, as a string.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>right_operand</parameter></term>
<listitem>
<para>
The right operand, as a string.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>modulus</parameter></term>
<listitem>
<para>
The modulus, as a string.
</para>
</listitem>
</varlistentry>
&bc.scale.description;
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns the result as a string, or &null; if <parameter>modulus</parameter>
is 0.
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
<note>
<para>
Because this method uses the modulus operation, non-natural numbers
may give unexpected results. A natural number is any positive
non-zero integer.
</para>
</note>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
The following two statements are functionally identical. The
<function>bcpowmod</function> version however, executes in
less time and can accept larger parameters.
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
$a = bcpowmod($x, $y, $mod);
$b = bcmod(bcpow($x, $y), $mod);
// $a and $b are equal to each other.
?>
]]>
</programlisting>
</informalexample>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>bcpow</function></member>
<member><function>bcmod</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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