Performance snippet – arrays in c# (for x86 compilers)

Here are some rules for working with array in .net when performance is critical. Some demand from you nothing but knowing about them with no special implementation implications, other require making decisions that require more attention (such as using unsafe code or even unmanaged code).

It's better to use jagged arrays (array or arrays) rather than multidimensional arrays
Within the CLR there is an optimization for loops that has a termination checkpoint against the length property of the collection/array. However this is not implemented for multidimensional arrays.In order to achieve better performance when the need arises to use multidimensional arrays it's better to use Jagged arrays
Example of a jagged array:int[][] arrJagged = new int[][]{new int[]{1,2,3,4,5},new int[]{2,3,4,5,6}};

Always use ascending loops
Well its even a better coding practice. Not only that your loop would be easier to read and understand it will also enjoy the benefit of better performance.
In a regular ascending loop the compiler statically checks that we are in the boundaries of the array, thus preventing the need for further checks on runtime. But, this feature is not implemented for descending loops which means that for each access by index a to the array a dynamic range check would be performed on runtime, reducing code speed…
But, pay attention. If you write this code

Private double[] GenerateAndPopulate(int iSize)
{
   double[] arr = new double[iSize];
   for(int I=0 ; I < iSize ; i++)
   {
      Arr[i] = i;
   }
}

You would not enjoy the termination of dynamic bound checks since. The right way (in terms of performance) is to use arr.Lenght

To be continued soon….