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<?xml version="1.0" encoding="utf-8"?>
<refentry xml:id="bcmath-number.powmod" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude">
<refnamediv>
<refname>BcMath\Number::powmod</refname>
<refpurpose>Raises an arbitrary precision number, reduced by a specified modulus</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis role="BcMath\\Number">
<modifier>public</modifier> <type>BcMath\Number</type><methodname>BcMath\Number::powmod</methodname>
<methodparam><type class="union"><type>BcMath\Number</type><type>string</type><type>int</type></type><parameter>exponent</parameter></methodparam>
<methodparam><type class="union"><type>BcMath\Number</type><type>string</type><type>int</type></type><parameter>modulus</parameter></methodparam>
<methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>scale</parameter><initializer>&null;</initializer></methodparam>
</methodsynopsis>
<simpara>
Use the fast-exponentiation method to raise <varname>$this</varname> to the power
<parameter>exponent</parameter> with respect to the modulus <parameter>modulus</parameter>.
</simpara>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<variablelist>
<varlistentry>
<term><parameter>exponent</parameter></term>
<listitem>
<simpara>
The exponent, as an non-negative and integral (i.e. the scale has to be zero).
</simpara>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>modulus</parameter></term>
<listitem>
<simpara>
The modulus, as an integral (i.e. the scale has to be zero).
</simpara>
</listitem>
</varlistentry>
<xi:include xpointer="xmlns(db=http://docbook.org/ns/docbook) xpointer(id('bcmath-number.add')/db:refsect1[@role='parameters']/descendant::db:varlistentry[2])" />
</variablelist>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<simpara>
Returns the result as a new <classname>BcMath\Number</classname> object.
</simpara>
<simpara>
When the <property>BcMath\Number::scale</property> of the result object is automatically set,
the <property>BcMath\Number::scale</property> of the result object will always be <literal>0</literal>.
</simpara>
</refsect1>
<refsect1 role="errors">
&reftitle.errors;
<para>
This method throws a <exceptionname>ValueError</exceptionname> in the following cases:
<simplelist>
<member><parameter>exponent</parameter> or <parameter>modulus</parameter> is <type>string</type> and not
a well-formed BCMath numeric string</member>
<member><varname>$this</varname>, <parameter>exponent</parameter> or <parameter>modulus</parameter> has a fractional part</member>
<member><parameter>exponent</parameter> is a negative value</member>
<member><parameter>scale</parameter> is outside the valid range</member>
</simplelist>
</para>
<simpara>
This method throws a <exceptionname>DivisionByZeroError</exceptionname> exception if <parameter>modulus</parameter>
is <literal>0</literal>.
</simpara>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<example>
<title><methodname>BcMath\Number::powmod</methodname> example when <parameter>scale</parameter> is not specified</title>
<programlisting role="php">
<![CDATA[
<?php
var_dump(
new BcMath\Number('8')->powmod(new BcMath\Number('3'), 5),
new BcMath\Number('-8')->powmod(new BcMath\Number('3'), 5),
new BcMath\Number('8')->powmod('2', -3),
new BcMath\Number('-8')->powmod(5, 7),
);
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
object(BcMath\Number)#3 (2) {
["value"]=>
string(1) "2"
["scale"]=>
int(0)
}
object(BcMath\Number)#4 (2) {
["value"]=>
string(2) "-2"
["scale"]=>
int(0)
}
object(BcMath\Number)#2 (2) {
["value"]=>
string(1) "1"
["scale"]=>
int(0)
}
object(BcMath\Number)#5 (2) {
["value"]=>
string(2) "-1"
["scale"]=>
int(0)
}
]]>
</screen>
</example>
<example>
<title><methodname>BcMath\Number::powmod</methodname> example of explicitly specifying <parameter>scale</parameter></title>
<programlisting role="php">
<![CDATA[
<?php
var_dump(
new BcMath\Number('8')->powmod(new BcMath\Number('3'), 5, 1),
new BcMath\Number('-8')->powmod(new BcMath\Number('3'), 5, 2),
new BcMath\Number('8')->powmod('2', -3, 3),
new BcMath\Number('-8')->powmod(5, 7, 4),
);
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
object(BcMath\Number)#3 (2) {
["value"]=>
string(3) "2.0"
["scale"]=>
int(1)
}
object(BcMath\Number)#4 (2) {
["value"]=>
string(5) "-2.00"
["scale"]=>
int(2)
}
object(BcMath\Number)#2 (2) {
["value"]=>
string(5) "1.000"
["scale"]=>
int(3)
}
object(BcMath\Number)#5 (2) {
["value"]=>
string(7) "-1.0000"
["scale"]=>
int(4)
}
]]>
</screen>
</example>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<simplelist>
<member><function>bcpowmod</function></member>
<member><methodname>BcMath\Number::pow</methodname></member>
<member><methodname>BcMath\Number::mod</methodname></member>
</simplelist>
</refsect1>
</refentry>
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