Wordpress: Additional post classes

gistfile1

<?php
function additional_post_classes( $classes ) {
  global $wp_query;

  if( $wp_query->found_posts < 1 ) {
    return $classes;
  }

  if( $wp_query->current_post == 0 ) {
    $classes[] = 'post-first';
  }

  if( $wp_query->current_post % 2 ) {
    $classes[] = 'post-even';
  } else {
    $classes[] = 'post-odd';
  }

  if( $wp_query->current_post == ( $wp_query->post_count - 1 ) ) {
    $classes[] = 'post-last';
  }

  return $classes;
}
add_filter( 'post_class', 'additional_post_classes' );
?>