function saveExtent() {
    /* save the current extent in a cookie */
    if(!map) return;
    document.cookie = "MAP_EXTENT=" + map.getExtent().toArray().join('_')
                      + ';path="/"';
}

function getExtent() {
    /* get the current extent from a cookie */
    var cookies = document.cookie.split(';');
    var map_extent;
    for (i in cookies){
        var items = cookies[i].split('=');
        if (items[0] == 'MAP_EXTENT') map_extent = items[1].split('_');
    }
    return map_extent;
}

function zoomToCurrentExtent(map){
    /* zoom to current extent */
    var current_extent = getExtent();
    if (OpenLayers && current_extent && current_extent.length == 4){
        extent = new OpenLayers.Bounds(current_extent[0], current_extent[1],
                                       current_extent[2], current_extent[3]);
        map.zoomToExtent(extent, true);
        return true;
    }
    else{
        return;
    }
}