int crc32(string $str)

(PHP 4 >= 4.01, PHP 5)

Use this method to calculate the Cyclical Redundancy Check (checksum) for string or binary data. The result is a signed integer, if you want to convert it to signed, you will need to convert the result using sprintf as shown in the example below.

// calulate the checksum from a form post
$chksum = crc32($_POST['body']);
echo sprintf('The checksum is: %u', $chksum);