For arbitrary precision mathematics PHP offers the Binary Calculator which supports numbers of any size and precision, represented as strings.
In PHP 4, these functions are only available if PHP was configured with --enable-bcmath. In PHP 3, these functions are only available if PHP was not configured with --disable-bcmath.
Note: Due to changes in the licensing, the BCMATH library is distributed separate from the standard PHP source distribution. You can download the tar-gzipped archive at the url: http://www.php.net/extra/number4.tar.gz. Read the file README.BCMATH in the PHP distribution for more information.