function checkdata(){
    var f=document.log_form
    if(!f.username.value.match(/^[A-Za-z0-9]{5,20}$/i)){alert("\用户名应该由不区分大小写的a-z 0-9字符组成！");f.username.focus();return false}
    if(f.password.value.length < 6){alert("密码不能小于6位");f.password.focus();return false}
    if(f.password.value.length > 20){alert("密码不能大于16位");f.password.focus();return false}
    if(f.yzm.value.length != 3 ){alert("验证码位数不对");f.yzm.focus();return false}
    }

document.write('<div class="user"><div class="unlogin" id="not_login_box"><a href="/u/reg.asp" target="_blank" title="注册game19平台帐号" class="regbtn png">注册game19平台帐号</a><h2>用户登录</h2><div class="login_form"><form id="log_form" name="log_form" method="post" action="/u/login_check.asp" onsubmit="return checkdata()"><div class="ubox name_box"><label>帐号：</label><input id="username" tabindex="1" name="username" type="text" class="intxt" /></div><div class="ubox"><label>密码：</label><input type="password" tabindex="2" id="password" name="password"  class="intxt" /></div><div class="ubox chkbox"><p class="tips" id="logintips"></p></div></div><input type="submit" id="login_button_y" tabindex="4" class="btn login" value="登陆" /><div class="links"><a href="/u/forgetpwd.asp" target="_blank" title="">忘记密码？</a></form></div></div></div>');