Why do UInt16 arrays seem to add faster than int arrays?
- by scraimer
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:
Creates two arrays named a and b, once.
Fills them with random data, once.
Starts a stopwatch.
Adds a and b, item-by-item. This is done 1000 times.
Stops the stopwatch.
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)");
}
