<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Check if number is "probably prime"</title> </head> <body><div class="manualnavbar" style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.gmp-powm.html">gmp_powm</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.gmp-random-bits.html">gmp_random_bits</a></div> <div class="up"><a href="ref.gmp.html">GMP Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div> </div><hr /><div id="function.gmp-prob-prime" class="refentry"> <div class="refnamediv"> <h1 class="refname">gmp_prob_prime</h1> <p class="verinfo">(PHP 4 >= 4.0.4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">gmp_prob_prime</span> — <span class="dc-title">Check if number is "probably prime"</span></p> </div> <div class="refsect1 description" id="refsect1-function.gmp-prob-prime-description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type">int</span> <span class="methodname"><strong>gmp_prob_prime</strong></span> ( <span class="methodparam"><span class="type"><a href="class.gmp.html" class="type GMP">GMP</a></span> <code class="parameter">$a</code></span> [, <span class="methodparam"><span class="type">int</span> <code class="parameter">$reps</code><span class="initializer"> = 10</span></span> ] )</div> <p class="para rdfs-comment"> The function uses Miller-Rabin's probabilistic test to check if a number is a prime. </p> </div> <div class="refsect1 parameters" id="refsect1-function.gmp-prob-prime-parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <code class="parameter">a</code></dt> <dd> <p class="para"> The number being checked as a prime. </p> <p class="para">Either a GMP number <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span> in PHP 5.5 and earlier, a <a href="class.gmp.html" class="classname">GMP</a> object in PHP 5.6 and later, or a numeric string provided that it is possible to convert the latter to a number.</p> </dd> <dt> <code class="parameter">reps</code></dt> <dd> <p class="para"> Reasonable values of <code class="parameter">reps</code> vary from 5 to 10 (default being 10); a higher value lowers the probability for a non-prime to pass as a "probable" prime. </p> <p class="para">Either a GMP number <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span> in PHP 5.5 and earlier, a <a href="class.gmp.html" class="classname">GMP</a> object in PHP 5.6 and later, or a numeric string provided that it is possible to convert the latter to a number.</p> </dd> </dl> </p> </div> <div class="refsect1 returnvalues" id="refsect1-function.gmp-prob-prime-returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> If this function returns 0, <code class="parameter">a</code> is definitely not prime. If it returns 1, then <code class="parameter">a</code> is "probably" prime. If it returns 2, then <code class="parameter">a</code> is surely prime. </p> </div> <div class="refsect1 examples" id="refsect1-function.gmp-prob-prime-examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example" id="example-4220"> <p><strong>Example #1 <span class="function"><strong>gmp_prob_prime()</strong></span> example</strong></p> <div class="example-contents"> <div class="phpcode"><code><span style="color: #000000"> <span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// definitely not a prime<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">gmp_prob_prime</span><span style="color: #007700">(</span><span style="color: #DD0000">"6"</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// probably a prime<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">gmp_prob_prime</span><span style="color: #007700">(</span><span style="color: #DD0000">"1111111111111111111"</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// definitely a prime<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">gmp_prob_prime</span><span style="color: #007700">(</span><span style="color: #DD0000">"11"</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span> </span> </code></div> </div> <div class="example-contents"><p>The above example will output:</p></div> <div class="example-contents screen"> <div class="cdata"><pre> 0 1 2 </pre></div> </div> </div> </p> </div> </div><hr /><div class="manualnavbar" style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.gmp-powm.html">gmp_powm</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.gmp-random-bits.html">gmp_random_bits</a></div> <div class="up"><a href="ref.gmp.html">GMP Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div> </div></body></html>