Massive Multiplication

<!-- if, for some reason, you ever wanted super precise unlimited multiplication, then here you have it -->
<!-- only limited to where the carry over is greater than 9007199254740992 -->
<!-- I think your computer would've ran out of memory by then -->

<!-- Actually on second thought, the stack would overflow far sooner than reaching an actual limit -->
<script>
function MShift(res,i,j)
{
 var dy=0,dx=0;
 if(j>0)dx=1;
 else if(i>0) dy=1;
 else return;
 var rem = res[i][j]%10;
 var car = (res[i][j]-rem)/10;
 res[i-dy][j-dx]+=car;
 res[i][j]=rem;
 if(res[i-dy][j-dx]>9)MShift(res,i-dy,j-dx);
}
function Multiply(a,b)
{
 a=a.toString();
 b=b.toString();
 var adot = a.length-a.indexOf(".")-1;
 var bdot = b.length-b.indexOf(".")-1;
 if(adot==a.length)adot=0;
 if(bdot==b.length)bdot=0;
 var dotpos = adot+bdot;
 a = a.replace(/\./g,"");
 b = b.replace(/\./g,"");
 var al=a.length;
 var bl=b.length;
 if(al==0||bl==0)return NaN;
 var res = [];
 for(var i=0; i<al; i++)
 {
  res[i] = [];
  for(var j=0; j<bl; j++)
  {
   res[i][j] = a[i]*b[j]+(i>0&&j<bl-1?res[i-1][j+1]:0);
   if(res[i][j]>9)MShift(res,i,j);
  }
 }
 for(var i=0; i<al-1; i++)
 {
  res[i] = res[i][0];
 }
 var ret = res.toString().replace(/,/g,"");
 if(dotpos>0)ret = ret.substring(0,ret.length-dotpos)+"."+ret.substring(ret.length-dotpos);
 return ret;
}
function doMult()
{
 var left = document.getElementById("left");
 var right = document.getElementById("right");
 var out = document.getElementById("out");
 out.innerHTML = Multiply(left.value,right.value);
}
</script>
<input id="left" oninput="doMult()" /> x <input id="right" oninput="doMult()" /> = <span id="out"></span>