function set_cookie ( cookie_name, cookie_value, lifespan_in_days, valid_domain )
{
    // http://www.thesitewizard.com/javascripts/cookies.shtml
    var domain_string = valid_domain ? ("; domain=" + valid_domain) : '';
    document.cookie = cookie_name + "=" + encodeURIComponent( cookie_value ) + "; max-age=" + 60 * 60 * 24 * lifespan_in_days + "; path=/" + domain_string;
}

function get_cookie ( cookie_name )
{
    var cookie_string = " " + document.cookie ;
    var search = " " + escape(cookie_name) + "=";
	var setStr = null;
	var offset = 0;
	var end = 0; 
    if (cookie_string.length > 0) {
		offset = cookie_string.indexOf(search);
		if (offset!= -1) {
			offset += search.length;
			end = cookie_string.indexOf(";", offset);
			if (end == -1) {
				end = cookie_string.length;
			}
			setStr = unescape(cookie_string.substring(offset, end));
		}
	}
	return(setStr);    
}