// ypChaser
function ypChaser(sLayerId, iTopOffset, iSlideTime, iCeiling, iFloor) {
	this.chaserDiv = null
	this.layerId = sLayerId
	this.topOffset = iTopOffset
	this.slideTime = iSlideTime
	this.ceiling = iCeiling
	this.floor = iFloor
	ypChaser.registry[ypChaser.registry.length] = this
	}
	ypChaser.isIE = window.clientInformation ? true : false
	ypChaser.isIEDTD = ((document.doctype && document.doctype.name.indexOf(".dtd")>-1) || document.compatMode == "CSS1Compat") ? true : false;
	ypChaser.isN4 = document.layers ? true : false
	ypChaser.isN6 = navigator.appName == "Netscape" && parseInt(navigator.appVersion) >= 5
	ypChaser.isO5 = navigator.userAgent.indexOf("Opera") != -1 && parseInt(navigator.appVersion) >= 4
	ypChaser.registry = new Array( )
	ypChaser.callRate = 10
	window.setInterval("ypChaser.timer( )", ypChaser.callRate)
	ypChaser.timer = function() {
	for (var i = 0; chObj = this.registry[i]; i++) {
		if (!chObj.chaserDiv) chObj.attemptLoad()
		if (chObj.chaserDiv) chObj.main()
	}
}
ypChaser.prototype.attemptLoad = function() {
	var chDiv = null
	if (ypChaser.isN6 || ypChaser.isO5) chDiv = document.getElementById(this.layerId)
	else if (ypChaser.isIE) chDiv = document.all[this.layerId]
	else if (ypChaser.isN4) chDiv = document.layers[this.layerId]
	if (chDiv && chDiv != null) {
		this.chaserDiv = chDiv
	}
}

ypChaser.prototype.main = function( ){
	this.currentY = this.getCurrentY()
	var scrollTop = ypChaser.getWindowScroll()
	var newTargetY = scrollTop + this.topOffset
	var floor = ypChaser.getDocumentHeight() - this.floor
	newTargetY = Math.max( newTargetY, this.ceiling)
	if (!ypChaser.isO5) newTargetY = Math.min(newTargetY, floor)
	if ( this.currentY != newTargetY ) {
		if ( newTargetY != this.targetY ) {
			this.targetY = newTargetY
			this.slideInit( )
		}
		this.slide( )
	}
}

ypChaser.prototype.slideInit = function( ){
	this.A = (this.targetY - this.currentY) / this.slideTime / this.slideTime
	this.startT = (new Date()).getTime()
	this.startP = this.getCurrentY()
	this.D = this.targetY - this.startP
}

ypChaser.prototype.slide = function( ){
	var elapsed = (new Date()).getTime() - this.startT
	if (elapsed < this.slideTime) {
		this.moveTo(this.D - (Math.round(Math.pow(this.slideTime - elapsed, 2) * this.A)) + this.startP)
	}
}

ypChaser.prototype.moveTo = function(ny) {
	if (ypChaser.isN4) this.chaserDiv.top = ny
	else this.chaserDiv.style.top = ny + "px"
}

ypChaser.prototype.getCurrentY = function() {
	var n = ypChaser.isN4 ? this.chaserDiv.top : parseInt(this.chaserDiv.style.top)
	return isNaN(n) ? 0 : n
}

ypChaser.getWindowScroll = function() {
	if (ypChaser.isIEDTD) {
		window.status=document.documentElement.scrollTop;
		return document.documentElement.scrollTop;
	}
	else if (ypChaser.isIE) return document.body.scrollTop;
	else return window.pageYOffset
}
ypChaser.getDocumentHeight = function() {
	if (ypChaser.isO5) return 0 // opera can't retreive this property.
	else if (ypChaser.isIEDTD) return Math.max(document.documentElement.scrollHeight, document.documentElement.offsetHeight)
	else if (ypChaser.isIE) return Math.max(document.body.scrollHeight, document.body.offsetHeight)
	else return window.document.height
}