JS滚动代码出现问题，请教大家
代码如下所示，问题是第二轮滚动到第三行时，第三行显示了两次。
程序代码：<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www. xmlns="http://www. http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>上滚</title>
</head>
<body>
<div id="gg" style=" width:1000px; height:30px;">
<table width="1000" border="0" cellpadding="0" cellspacing="0" id="ggtab">
<tr>
<td height="30" bgcolor="#CCCCCC">1111</td>
</tr>
<tr>
<td height="30" bgcolor="#F2F2F2">2222</td>
</tr>
<tr>
<td height="30" bgcolor="#CCCCCC">3333</td>
</tr>
</table>
</div>
<script type="text/javascript">
var o = document.getElementById("gg");
var tabo = document.getElementById("ggtab");
var marqueesHeight = 30;
var stopscroll=false;
with(o){
style.width=1000;
style.height=marqueesHeight;
style.overflow="hidden";
noWrap=true;
onmouseover=new Function("stopscroll=true");
onmouseout=new Function("stopscroll=false");
}
preTop=0; currentTop=marqueesHeight; stoptime=0;
o.innerHTML+=o.innerHTML;
function init_srolltext(){
o.scrollTop=0;
setInterval("scrollUp2()",1);
}
function scrollUp2(){
if(stopscroll==true) return;
currentTop+=5;
if(currentTop>marqueesHeight+1)
{
stoptime+=1;
currentTop=marqueesHeight;
if(stoptime==100)
{
currentTop=0;
stoptime=0;
}
}
else {
preTop=o.scrollTop;
o.scrollTop+=5;
if(preTop>=o.scrollTop){
o.scrollTop=marqueesHeight;
o.scrollTop+=5;
}
}
}
init_srolltext();
</script>
</body>
</html>
