What is the fastest way to Initialize a multi-dimensional array to non-default values in .NET?
- by AMissico
How do I initialize a multi-dimensional array of a primitive type as fast as possible?
I am stuck with using multi-dimensional arrays. My problem is performance. The following routine initializes a 100x100 array in approx. 500 ticks. Removing the int.MaxValue initialization results in approx. 180 ticks just for the looping. Approximately 100 ticks to create the array without looping and without initializing to int.MaxValue.
Routines similiar to this are called a few hundred-thousand to several million times during a "run".
The array size will not change during a run and arrays are created one-at-a-time, used, then discarded, and a new array created.
A "run" which may last from one minute (using 10x10 arrays) to forty-five minutes (100x100).
The application creates arrays of int, bool, and struct.
There can be multiple "runs" executing at same time, but are not because performance degrades terribly.
I am using 100x100 as a base-line.
I am open to suggestions on how to optimize this non-default initialization of an array. One idea I had is to use a smaller primitive type when available. For instance, using byte instead of int, saves 100 ticks. I would be happy with this, but I am hoping that I don't have to change the primitive data type.
public int[,] CreateArray(Size size) {
int[,] array = new int[size.Width, size.Height];
for (int x = 0; x < size.Width; x++) {
for (int y = 0; y < size.Height; y++) {
array[x, y] = int.MaxValue;
}
}
return array;
}
Down to 450 ticks with the following:
public int[,] CreateArray1(Size size) {
int iX = size.Width;
int iY = size.Height;
int[,] array = new int[iX, iY];
for (int x = 0; x < iX; x++) {
for (int y = 0; y < iY; y++) {
array[x, y] = int.MaxValue;
}
}
return array;
}
Down to approximately 165 ticks after a one-time initialization of 2800 ticks. (See my answer below.) If I can get stackalloc to work with multi-dimensional arrays, I should be able to get the same performance without having to intialize the private static array.
private static bool _arrayInitialized5;
private static int[,] _array5;
public static int[,] CreateArray5(Size size) {
if (!_arrayInitialized5) {
int iX = size.Width;
int iY = size.Height;
_array5 = new int[iX, iY];
for (int x = 0; x < iX; x++) {
for (int y = 0; y < iY; y++) {
_array5[x, y] = int.MaxValue;
}
}
_arrayInitialized5 = true;
}
return (int[,])_array5.Clone();
}
Down to approximately 165 ticks without using the "clone technique" above. (See my answer below.) I am sure I can get the ticks lower, if I can just figure out the return of CreateArray9.
public unsafe static int[,] CreateArray8(Size size) {
int iX = size.Width;
int iY = size.Height;
int[,] array = new int[iX, iY];
fixed (int* pfixed = array) {
int count = array.Length;
for (int* p = pfixed; count-- > 0; p++)
*p = int.MaxValue;
}
return array;
}
