<?php
function array_key_exists_test( $n )
{
    //setup the array
    $array = array();
    $set_key_count = (int)($n/2);
    for( $i = 0; $i < $set_key_count; $i++ ) {
        do {
            $rand_number = rand( 0, $n-1 );
        } while( array_key_exists( $rand_number, $array ) );
        $array[$rand_number] = NULL;
    }
    $test_array = range( 0, $n-1 );
    shuffle( $test_array );
    $result_array = array();

    $start = microtime(true);

    foreach( $test_array as $test_number ) {
        if( array_key_exists( $test_number, $array ) ) {
            $result_array[] = $test_number;
        }
    }

    $stop = microtime(true);

    if( count( $result_array ) !== $set_key_count )
        throw new Exception( "test failed" );

    return ( $stop - $start ) / $n;
}

$n_array = range( 1, 100 );
$n_array = array_map( function( $n ) { return $n * 10000; }, $n_array );
foreach( $n_array as $n ) {
    print sprintf( "at n of %d time per call %.10f\n", $n, array_key_exists_test( $n ) );
}

?>