function computed_field_field_highest_compute(&$entity_field, $entity_type, $entity, $field, $instance, $langcode, $items) {
  $temps = field_get_items($entity_type, $entity, 'field_temp');
  if (count($temps)) {
    $max = $temps[0]['value'];
    foreach($temps as $temp) {
      $max = $temp['value'] > $max ? $temp['value'] : $max;
    }
    $entity_field[0]['value'] = $max;
  }
}

function computed_field_field_lowest_compute(&$entity_field, $entity_type, $entity, $field, $instance, $langcode, $items) {
  $temps = field_get_items($entity_type, $entity, 'field_temp');
  if (count($temps)) {
    $min = $temps[0]['value'];
    foreach($temps as $temp) {
      $min = $temp['value'] < $min ? $temp['value'] : $min;
    }
    $entity_field[0]['value'] = $min;
  }
}