var  x  =  1,y  =  1
var  xin  =  true,  yin  =  true
var  step  =  1  
var  delay  =  30
var  obj=document.getElementById("ad")  
function  floatAD()  {
      var  L=T=0
      var  R=  document.body.clientWidth-obj.offsetWidth
      var  B  =  document.body.clientHeight-obj.offsetHeight
      obj.style.left  =  x  +  document.body.scrollLeft+"px";
      obj.style.top  =  y  +  document.body.scrollTop+"px";
      x  =  x  +  step*(xin?1:-1)    
      if  (x  <  L)  {  xin  =  true;  x  =  L}  
      if  (x  >  R){  xin  =  false;  x  =  R}  
      y  =  y  +  step*(yin?1:-1)  
      if  (y  <  T)  {  yin  =  true;  y  =  T  }  
      if  (y  >  B)  {  yin  =  false;  y  =  B  }  
}
var  itl=  setInterval("floatAD()",  delay)  
obj.onmouseover=function(){clearInterval(itl)}  
obj.onmouseout=function(){itl=setInterval("floatAD()",  delay)}