It seems that C# is faster at adding two arrays of UInt16[] than it is at adding two arrays of int[]. This makes no sense to me, since I would have assumed the arrays would be word-aligned, and thus int[] would require less work from the CPU, no?

I ran the test-code below, and got the following results:

Int    for 1000 took 9896625613 tick (4227 msec)
UInt16 for 1000 took 6297688551 tick (2689 msec)

The test code does the following:

1. Creates two arrays named a and b, once.
2. Fills them with random data, once.
3. Starts a stopwatch.
4. Adds a and b, item-by-item. This is done 1000 times.
5. Stops the stopwatch.
6. Reports how long it took.

This is done for int[] a, b and for UInt16 a,b. And every time I run the code, the tests for the UInt16 arrays take 30%-50% less time than the int arrays. Can you explain this to me?

Here's the code, if you want to try if for yourself:

public static UInt16[] GenerateRandomDataUInt16(int length)
{
    UInt16[] noise = new UInt16[length];
    Random random = new Random((int)DateTime.Now.Ticks);
    for (int i = 0; i < length; ++i)
    {
        noise[i] = (UInt16)random.Next();
    }

    return noise;
}

public static int[] GenerateRandomDataInt(int length)
{
    int[] noise = new int[length];
    Random random = new Random((int)DateTime.Now.Ticks);
    for (int i = 0; i < length; ++i)
    {
        noise[i] = (int)random.Next();
    }

    return noise;
}

public static int[] AddInt(int[] a, int[] b)
{
    int len = a.Length;
    int[] result = new int[len];
    for (int i = 0; i < len; ++i)
    {
        result[i] = (int)(a[i] + b[i]);
    }
    return result;
}

public static UInt16[] AddUInt16(UInt16[] a, UInt16[] b)
{
    int len = a.Length;
    UInt16[] result = new UInt16[len];
    for (int i = 0; i < len; ++i)
    {
        result[i] = (ushort)(a[i] + b[i]);
    }
    return result;
}


public static void Main()
{
    int count = 1000;
    int len = 128 * 6000;

    int[] aInt = GenerateRandomDataInt(len);
    int[] bInt = GenerateRandomDataInt(len);

    Stopwatch s = new Stopwatch();
    s.Start();
    for (int i=0; i<count; ++i) 
    {
        int[] resultInt = AddInt(aInt, bInt);
    }
    s.Stop();
    Console.WriteLine("Int    for " + count 
                + " took " + s.ElapsedTicks + " tick (" 
                + s.ElapsedMilliseconds + " msec)");

    UInt16[] aUInt16 = GenerateRandomDataUInt16(len);
    UInt16[] bUInt16 = GenerateRandomDataUInt16(len);

    s = new Stopwatch();
    s.Start();
    for (int i=0; i<count; ++i) 
    {
        UInt16[] resultUInt16 = AddUInt16(aUInt16, bUInt16);
    }
    s.Stop();
    Console.WriteLine("UInt16 for " + count 
                + " took " + s.ElapsedTicks + " tick (" 
                + s.ElapsedMilliseconds + " msec)");


}