Source

File: wp-includes/revision.php

function wp_get_post_revision( &$post, $output = OBJECT, $filter = 'raw' ) {
	$revision = get_post( $post, OBJECT, $filter );
	if ( ! $revision ) {
		return $revision;
	}
	if ( 'revision' !== $revision->post_type ) {
		return null;
	}

	if ( OBJECT == $output ) {
		return $revision;
	} elseif ( ARRAY_A == $output ) {
		$_revision = get_object_vars( $revision );
		return $_revision;
	} elseif ( ARRAY_N == $output ) {
		$_revision = array_values( get_object_vars( $revision ) );
		return $_revision;
	}

	return $revision;
}