JS滚动代码出现问题，请教大家 - 编程论坛

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>