bcpow.xml

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<refentry xml:id="function.bcpow" xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude">
 <refnamediv>
  <refname>bcpow</refname>
  <refpurpose>Raise an arbitrary precision number to another</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>string</type><methodname>bcpow</methodname>
   <methodparam><type>string</type><parameter>num</parameter></methodparam>
   <methodparam><type>string</type><parameter>exponent</parameter></methodparam>
   <methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>scale</parameter><initializer>&null;</initializer></methodparam>
  </methodsynopsis>
  <para>
   Raise <parameter>num</parameter> to the power 
   <parameter>exponent</parameter>. 
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>num</parameter></term>
     <listitem>
      <para>
       The base, as a string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>exponent</parameter></term>
     <listitem>
      <para>
       The exponent, as a string. Must be a value with no fractional part.
       The valid range of the exponent is platform specific, but is at least
       <literal>-2147483648</literal> to <literal>2147483647</literal>.
      </para>
     </listitem>
    </varlistentry>
    <xi:include xpointer="function.bcadd..parameters.scale" />
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the result as a string.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   This function throws a <exceptionname>ValueError</exceptionname> in the following cases:
   <simplelist>
    <member><parameter>num</parameter> or <parameter>exponent</parameter> is not a well-formed BCMath numeric string</member>
    <member><parameter>exponent</parameter> has a fractional part</member>
    <member><parameter>exponent</parameter> or <parameter>scale</parameter> is outside the valid range</member>
   </simplelist>
  </para>
  <simpara>
   This function throws a <exceptionname>DivisionByZeroError</exceptionname> exception if <parameter>num</parameter>
   is <literal>0</literal> and <parameter>exponent</parameter> is a negative value.
  </simpara>
 </refsect1>

 <refsect1 role="changelog"><!-- {{{ -->
  &reftitle.changelog;
  <informaltable>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>&Version;</entry>
      <entry>&Description;</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry>8.4.0</entry>
      <entry>
       Negative powers of <literal>0</literal> previously returned <literal>0</literal>, but now throw a <exceptionname>DivisionByZeroError</exceptionname>
       exception.
      </entry>
     </row>
     <row>
      <entry>8.0.0</entry>
      <entry>
       When <parameter>exponent</parameter> has a fractional part, it now throws a <exceptionname>ValueError</exceptionname>
       instead of truncating.
      </entry>
     </row>
     <row>
      <entry>7.3.0</entry>
      <entry>
       <function>bcpow</function> now returns numbers with the requested scale.
       Formerly, the returned numbers may have omitted trailing decimal zeroes.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </informaltable>
 </refsect1><!-- }}} -->

 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><function>bcpow</function> example</title>
   <programlisting role="php">
<![CDATA[
<?php

echo bcpow('4.2', '3', 2); // 74.08

?>
]]>
   </programlisting>
  </example>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    Before PHP 7.3.0 <function>bcpow</function> may return a result with fewer digits after the
    decimal point than the <parameter>scale</parameter> parameter would
    indicate. This only occurs when the result doesn't require all of the
    precision allowed by the <parameter>scale</parameter>. For example:
    <example>
     <title><function>bcpow</function> scale example</title>
     <programlisting role="php">
<![CDATA[
<?php
echo bcpow('5', '2', 2);     // prints "25", not "25.00"
?>
]]>
     </programlisting>
    </example>
   </para>
  </note>
 </refsect1>
 
 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>bcpowmod</function></member>
    <member><function>bcsqrt</function></member>
    <member><methodname>BcMath\Number::pow</methodname></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>
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