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<title>Raise an arbitrary precision number to another, reduced by a specified modulus</title>
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<div class="refnamediv">
<h1 class="refname">bcpowmod</h1>
<p class="verinfo">(PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">bcpowmod</span> — <span class="dc-title">Raise an arbitrary precision number to another, reduced by a specified modulus</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.bcpowmod-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">string</span> <span class="methodname"><strong>bcpowmod</strong></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$base</code></span>
, <span class="methodparam"><span class="type">string</span> <code class="parameter">$exponent</code></span>
, <span class="methodparam"><span class="type">string</span> <code class="parameter">$modulus</code></span>
[, <span class="methodparam"><span class="type">int</span> <code class="parameter">$scale</code><span class="initializer"> = 0</span></span>
] )</div>
<p class="para rdfs-comment">
Use the fast-exponentiation method to raise
<code class="parameter">base</code> to the power
<code class="parameter">exponent</code> with respect to the modulus
<code class="parameter">modulus</code>.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.bcpowmod-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">base</code></dt>
<dd>
<p class="para">
The base, as an integral string (i.e. the scale has to be zero).
</p>
</dd>
<dt>
<code class="parameter">exponent</code></dt>
<dd>
<p class="para">
The exponent, as an non-negative, integral string (i.e. the scale has to be zero).
</p>
</dd>
<dt>
<code class="parameter">modulus</code></dt>
<dd>
<p class="para">
The modulus, as an integral string (i.e. the scale has to be zero).
</p>
</dd>
<dt>
<code class="parameter">
scale</code></dt>
<dd>
<p class="para">This optional parameter is used to set the number
of digits after the decimal place in the result. If omitted, it will default to the scale set
globally with the <span class="function"><a href="function.bcscale.html" class="function">bcscale()</a></span> function, or fallback to <em>0</em> if
this has not been set.</p></dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.bcpowmod-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns the result as a string, or <strong><code>NULL</code></strong> if <code class="parameter">modulus</code>
is <em>0</em> or <code class="parameter">exponent</code> is negative.
</p>
</div>
<div class="refsect1 notes" id="refsect1-function.bcpowmod-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Because this method uses the modulus operation, numbers which are not
positive integers may give unexpected results.
</p>
</p></blockquote>
</div>
<div class="refsect1 examples" id="refsect1-function.bcpowmod-examples">
<h3 class="title">Examples</h3>
<p class="para">
The following two statements are functionally identical. The
<span class="function"><strong>bcpowmod()</strong></span> version however, executes in
less time and can accept larger parameters.
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$a </span><span style="color: #007700">= </span><span style="color: #0000BB">bcpowmod</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">, </span><span style="color: #0000BB">$y</span><span style="color: #007700">, </span><span style="color: #0000BB">$mod</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">= </span><span style="color: #0000BB">bcmod</span><span style="color: #007700">(</span><span style="color: #0000BB">bcpow</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">, </span><span style="color: #0000BB">$y</span><span style="color: #007700">), </span><span style="color: #0000BB">$mod</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// $a and $b are equal to each other.<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.bcpowmod-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.bcpow.html" class="function" rel="rdfs-seeAlso">bcpow()</a> - Raise an arbitrary precision number to another</span></li>
<li class="member"><span class="function"><a href="function.bcmod.html" class="function" rel="rdfs-seeAlso">bcmod()</a> - Get modulus of an arbitrary precision number</span></li>
</ul>
</p>
</div>
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