Math.easeOutQuad = function (t, b, c, d) { t /= d; return -c * t*(t-2) + b; };

(function() { // do not mess global space
var
	interval, // scroll is being eased
	mult = 0, // how fast do we scroll
	dir = 0, // 1 = scroll down, -1 = scroll up
	steps = 50, // how many steps in animation
	length = 30; // how long to animate
function MouseWheelHandler(e) {
	e.preventDefault(); // prevent default browser scroll
	clearInterval(interval); // cancel previous animation
	++mult; // we are going to scroll faster
	var delta = -Math.max(-1, Math.min(1, (e.wheelDelta || -e.detail))); // cross-browser
	if(dir!=delta) { // scroll direction changed
		mult = 1; // start slowly
		dir = delta;
	}
	// in this cycle, we determine which element to scroll
	for(var tgt=e.target; tgt!=document.documentElement; tgt=tgt.parentNode) {
		var oldScroll = tgt.scrollTop;
		tgt.scrollTop+= delta;
		if(oldScroll!=tgt.scrollTop) break;
		// else the element can't be scrolled, try its parent in next iteration
	}
	var start = tgt.scrollTop;
	var end = start + length*mult*delta; // where to end the scroll
	var change = end - start; // base change in one step
	var step = 0; // current step
	interval = setInterval(function() {
		var pos = Math.easeOutQuad(step++,start,change,steps); // calculate next step
		tgt.scrollTop = pos; // scroll the target to next step
		if(step>=steps) { // scroll finished without speed up - stop animation
			mult = 0; // next scroll will start slowly
			clearInterval(interval);
		}
	},10);
}

// nonstandard: Chrome, IE, Opera, Safari
window.addEventListener("mousewheel", MouseWheelHandler, false);
// nonstandard: Firefox
window.addEventListener("DOMMouseScroll", MouseWheelHandler, false);
})();