The source code

    /*!
     * Ext JS Library 3.3.1
     * Copyright(c) 2006-2010 Sencha Inc.
     * licensing@sencha.com
     * http://www.sencha.com/license
     */
    Ext.ns('Ext.calendar');

     (function() {
        Ext.apply(Ext.calendar, {
            Date: {
                diffDays: function(start, end) {
                    day = 1000 * 60 * 60 * 24;
                    diff = end.clearTime(true).getTime() - start.clearTime(true).getTime();
                    return Math.ceil(diff / day);
                },

                copyTime: function(fromDt, toDt) {
                    var dt = toDt.clone();
                    dt.setHours(
                    fromDt.getHours(),
                    fromDt.getMinutes(),
                    fromDt.getSeconds(),
                    fromDt.getMilliseconds());

                    return dt;
                },

                compare: function(dt1, dt2, precise) {
                    if (precise !== true) {
                        dt1 = dt1.clone();
                        dt1.setMilliseconds(0);
                        dt2 = dt2.clone();
                        dt2.setMilliseconds(0);
                    }
                    return dt2.getTime() - dt1.getTime();
                },

                // private helper fn
                maxOrMin: function(max) {
                    var dt = (max ? 0: Number.MAX_VALUE),
                    i = 0,
                    args = arguments[1],
                    ln = args.length;
                    for (; i < ln; i++) {
                        dt = Math[max ? 'max': 'min'](dt, args[i].getTime());
                    }
                    return new Date(dt);
                },

                max: function() {
                    return this.maxOrMin.apply(this, [true, arguments]);
                },

                min: function() {
                    return this.maxOrMin.apply(this, [false, arguments]);
                }
            }
        });
    })();