为什么处理排序数组比未排序数组慢?

我有一个500000随机生成的Tuple<long,long,string>对象的列表，我正在对其执行简单的“between”搜索:

var data = new List<Tuple<long,long,string>>(500000);
...
var cnt = data.Count(t => t.Item1 <= x && t.Item2 >= x);

当我生成随机数组并搜索100个随机生成的x值时，搜索大约在4秒内完成。知道了排序对搜索的巨大作用，然而，我决定对我的数据进行排序——首先是Item1，然后是Item2，最后是Item3——在运行我的100次搜索之前。由于分支预测，我期望排序版本执行得稍微快一点:我的想法是，一旦我们到达Item1 == x，所有对t.Item1 <= x的进一步检查都将正确地预测分支为“no take”，从而加快搜索的尾部部分。令我惊讶的是，在一个排序的数组上，搜索需要两倍的时间!

我试着改变我运行实验的顺序，并为随机数生成器使用不同的种子，但效果是相同的:在未排序数组中搜索的速度几乎是在相同数组中搜索的两倍，但已排序!

有人能很好地解释这个奇怪的效应吗?下面是我测试的源代码;我使用的是。net 4.0。

private const int TotalCount = 500000;
private const int TotalQueries = 100;
private static long NextLong(Random r) {
var data = new byte[8];
r.NextBytes(data);
return BitConverter.ToInt64(data, 0);
}
private class TupleComparer : IComparer<Tuple<long,long,string>> {
public int Compare(Tuple<long,long,string> x, Tuple<long,long,string> y) {
var res = x.Item1.CompareTo(y.Item1);
if (res != 0) return res;
res = x.Item2.CompareTo(y.Item2);
return (res != 0) ? res : String.CompareOrdinal(x.Item3, y.Item3);
}
}
static void Test(bool doSort) {
var data = new List<Tuple<long,long,string>>(TotalCount);
var random = new Random(1000000007);
var sw = new Stopwatch();
sw.Start();
for (var i = 0 ; i != TotalCount ; i++) {
var a = NextLong(random);
var b = NextLong(random);
if (a > b) {
var tmp = a;
a = b;
b = tmp;
}
var s = string.Format("{0}-{1}", a, b);
data.Add(Tuple.Create(a, b, s));
}
sw.Stop();
if (doSort) {
data.Sort(new TupleComparer());
}
Console.WriteLine("Populated in {0}", sw.Elapsed);
sw.Reset();
var total = 0L;
sw.Start();
for (var i = 0 ; i != TotalQueries ; i++) {
var x = NextLong(random);
var cnt = data.Count(t => t.Item1 <= x && t.Item2 >= x);
total += cnt;
}
sw.Stop();
Console.WriteLine("Found {0} matches in {1} ({2})", total, sw.Elapsed, doSort ? "Sorted" : "Unsorted");
}
static void Main() {
Test(false);
Test(true);
Test(false);
Test(true);
}

Populated in 00:00:01.3176257
Found 15614281 matches in 00:00:04.2463478 (Unsorted)
Populated in 00:00:01.3345087
Found 15614281 matches in 00:00:08.5393730 (Sorted)
Populated in 00:00:01.3665681
Found 15614281 matches in 00:00:04.1796578 (Unsorted)
Populated in 00:00:01.3326378
Found 15614281 matches in 00:00:08.6027886 (Sorted)