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copied!<p>Just to further reiterate how important performance testing is I ran the following test on my Core i5-750 in 64-bit native and 32-bit mode on Windows 7 compiled with VS 2010 targetting .NET 4.0 and got the following results:</p> <pre><code> public static bool DoSomething(double[] args) { bool ret = false; for (int i = 0; i < args.Length; i++) { if (double.IsNaN(args[i])) { ret = !ret; } } return ret; } public static bool DoSomething2(double[] args) { bool ret = false; for (int i = 0; i < args.Length; i++) { if (args[i] != args[i]) { ret = !ret; } } return ret; } public static IEnumerable<R> Generate<R>(Func<R> func, int num) { for (int i = 0; i < num; i++) { yield return func(); } } static void Main(string[] args) { Random r = new Random(); double[] data = Generate(() => { var res = r.NextDouble(); return res < 0.5 ? res : Double.NaN; }, 1000000).ToArray(); Stopwatch sw = new Stopwatch(); sw.Start(); DoSomething(data); Console.WriteLine(sw.ElapsedTicks); sw.Reset(); sw.Start(); DoSomething2(data); Console.WriteLine(sw.ElapsedTicks); Console.ReadKey(); } </code></pre> <p>In x86 mode (Release, naturally):</p> <pre><code>DoSomething() = 139544 DoSomething2() = 137924 </code></pre> <p>In x64 mode:</p> <pre><code>DoSomething() = 19417 DoSomething2() = 17448 </code></pre> <p>However, something interesting happens if our distribution of <code>NaN</code>'s is sparser. If we change our <code>0.5</code> constant to <code>0.9</code> (only 10% NaN's) we get:</p> <p>x86:</p> <pre><code>DoSomething() = 31483 DoSomething2() = 31731 </code></pre> <p>x64:</p> <pre><code>DoSomething() = 31432 DoSomething2() = 31513 </code></pre> <p>Reordering the calls shows the same trend as well. Food for thought.</p>

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