Smooth scrolling on scroll up/down

Smooth scrolling on scroll up/down

I need to animate a scroll from the current screen position up or down, when the scrollbar move up or down.

I'm using this script, but doesn't work ok:

 
    
  
  1. var iScrollPos = 0;
    2. 
  
  2.  $(window).scroll(function () {
    3. 
  
  3.  var iCurScrollPos = $(this).scrollTop();
    4. 
  
  4.  if (iCurScrollPos > iScrollPos) {
    5. 
  
  5.  $('html,body').animate({
    6. 
  
  6.  scrollTop: $(window).scrollTop() + 100
    7. 
  
  7.  })
    8. 
  
  8.  } else {
    9. 
  
  9.  $('html,body').animate({
    10. 
  
  10.  scrollTop: $(window).scrollTop() - 100
    11. 
  
  11.  })
    12. 
  
  12.  }
    13. 
  
  13.  iScrollPos = iCurScrollPos;
    14. 
  
  14. });
    15.

The problem is that a loop appear on the scroll down.