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<title>Calculates the crc32 polynomial of a string</title>
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<div class="refnamediv">
<h1 class="refname">crc32</h1>
<p class="verinfo">(PHP 4 >= 4.0.1, PHP 5)</p><p class="refpurpose"><span class="refname">crc32</span> — <span class="dc-title">Calculates the crc32 polynomial of a string</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.crc32-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">int</span> <span class="methodname"><strong>crc32</strong></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$str</code></span>
)</div>
<p class="para rdfs-comment">
Generates the cyclic redundancy checksum polynomial of 32-bit
lengths of the <em><code class="parameter">str</code></em>. This is usually used
to validate the integrity of data being transmitted.
</p>
<div class="warning"><strong class="warning">Warning</strong>
<p class="simpara">
Because PHP's integer type is signed many crc32 checksums will
result in negative integers on 32bit platforms. On 64bit installations
all <span class="function"><strong>crc32()</strong></span> results will be positive integers though.
</p>
<p class="simpara">
So you need to use the "%u" formatter of <span class="function"><a href="function.sprintf.html" class="function">sprintf()</a></span> or
<span class="function"><a href="function.printf.html" class="function">printf()</a></span> to get the string representation of the
unsigned <span class="function"><strong>crc32()</strong></span> checksum in decimal format.
</p>
<p class="simpara">
For a hexadecimal representation of the checksum you can either use the
"%x" formatter of <span class="function"><a href="function.sprintf.html" class="function">sprintf()</a></span> or <span class="function"><a href="function.printf.html" class="function">printf()</a></span>
or the <span class="function"><a href="function.dechex.html" class="function">dechex()</a></span> conversion functions, both of these
also take care of converting the <span class="function"><strong>crc32()</strong></span> result to
an unsigned integer.
</p>
<p class="simpara">
Having 64bit installations also return negative integers for higher
result values was considered but would break the hexadecimal conversion
as negatives would get an extra 0xFFFFFFFF######## offset then. As
hexadecimal representation seems to be the most common use case we
decided to not break this even if it breaks direct decimal comparisons
in about 50% of the cases when moving from 32 to 64bits.
</p>
<p class="simpara">
In retrospect having the function return an integer maybe wasn't the
best idea and returning a hex string representation right away (as
e.g. <span class="function"><a href="function.md5.html" class="function">md5()</a></span> does) might have been a better plan to
begin with.
</p>
<p class="simpara">
For a more portable solution you may also consider the generic
<span class="function"><a href="function.hash.html" class="function">hash()</a></span>. <code class="code">hash("crc32b", $str)</code> will
return the same string as <code class="code">dechex(crc32($str))</code>.
</p>
</div>
</div>
<div class="refsect1 parameters" id="refsect1-function.crc32-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">str</code></em></span>
<dd>
<p class="para">
The data.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.crc32-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns the crc32 checksum of <em><code class="parameter">str</code></em> as an integer.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.crc32-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-4823">
<p><strong>Example #1 Displaying a crc32 checksum</strong></p>
<div class="example-contents"><p>
This example shows how to print a converted checksum with the
<span class="function"><a href="function.printf.html" class="function">printf()</a></span> function:
</p></div>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$checksum </span><span style="color: #007700">= </span><span style="color: #0000BB">crc32</span><span style="color: #007700">(</span><span style="color: #DD0000">"The quick brown fox jumped over the lazy dog."</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"%u\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$checksum</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.crc32-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.hash.html" class="function" rel="rdfs-seeAlso">hash()</a> - Generate a hash value (message digest)</span></li>
<li class="member"> <span class="function"><a href="function.md5.html" class="function" rel="rdfs-seeAlso">md5()</a> - Calculate the md5 hash of a string</span></li>
<li class="member"> <span class="function"><a href="function.sha1.html" class="function" rel="rdfs-seeAlso">sha1()</a> - Calculate the sha1 hash of a string</span></li>
</ul>
</p>
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