sanitize-check.php

<?php
function absint( $maybeint ) {
		return abs( intval( $maybeint ) );
}

function sanitize_absint( $number = null ){
	// If it's not numeric we forget about it
	if ( ! is_numeric( $number ) ){
		return false;
	}

	// Split the String into multiple pieces (handles 32bits)
	$pieces = str_split( (string) $number );

	// Make sure every instance is an absolute integer no negatives
	$pieces = array_map( 'absint', $pieces );

	// Remove any items that are not numeric
	$pieces = array_filter( $pieces, 'is_numeric' );

	// If after all it's empty just return false
	if ( empty( $pieces ) ){
		return false;
	}

	// Glue everything and ship it
	return implode( '', $pieces );
}

function sanitize_regex( $val ) {
	// If it's not numeric we forget about it
	if ( ! is_numeric( $val ) ){
		return false;
	}

	$val = preg_replace( '/[^0-9]/', '', $val );

	if ( empty( $val ) ) {
		return false;
	}

	return $val;
}

define( 'NUM', 1000000 );

$val = '9437987349173409109378412094789027410987409127842930874902137414';
$start = microtime( true );
for ( $i = 0; $i < NUM; $i++ ) {
	sanitize_absint( $val );
}
$end = microtime( true );
echo 'Sanitize absint', $end - $start, ' seconds', "\n";
$start = microtime( true );
for ( $i = 0; $i < NUM; $i++ ) {
	sanitize_regex( $val );
}
$end = microtime( true );
echo 'Sanitize regex', $end - $start, ' seconds', "\n";