function AjaxSingin()
{
    var username    = document.getElementById('_username').value;
    var password    = document.getElementById('_password').value;
    var remember    = document.getElementById('_remember').checked;
    
    var reg = '^[\.a-zA-Z0-9_-]+$';
    
    if(!username.match(reg) || !password.match(reg) || username.length >= 45 || password.length >= 45) return false; 
    
    // cac thong so hoan hao
    if(remember) remember   = 'true';
    else remember   = 'false';
    
    var XMLhttp = getAjaxCore();
    
    // onreadystatechange
    XMLhttp.onreadystatechange  = function()
    {
        var inner       = document.getElementById('ajax_loading');
        
        var availWidth  = parseInt(document.documentElement.clientWidth)/2 - 300 + 'px';
        
        inner.style.left    = availWidth;
        inner.style.top     = 300 + 'px';
        
        inner.style.display = 'block';
        
        if(XMLhttp.readyState   != 4) {
            var img = '<center><img src="gui/ajax-loader3.gif"></center>'; 
            if(inner.innerHTML  != img) inner.innerHTML = img; 
        }
        
        // get return
        else {
            var response    = XMLhttp.responseText;
            
            if(response == 'true') { // dang nhap hop le
                var re  = '';
                inner.innerHTML = '<center>Log in ...</center>';
                
                location.href   = 'redirect.html';
                
            } else { // dang nhap khong hop le
                var conntent = '<span style="color:red;">Khong hop le</span>';
                inner.innerHTML = conntent;
            }
            
            
            
        }
        
        
        
    }
    
    // sending information
    var url = 'Ajax_script/writeCookie.ajax.php?username={username}&password={password}&remember={remember}&tmp={random}';
    
    // chuan hoa
    url = url.replace('{username}', encodeURIComponent(username));
    url = url.replace('{password}', encodeURIComponent(password));
    url = url.replace('{remember}', encodeURIComponent(remember));
    url = url.replace('{random}', Math.random());
    
    
    XMLhttp.open('GET', url, true);
    XMLhttp.send(null);
    
    
}