Implementing a sparse array in C# / fastest way to map integer to a specific bucket/range number

Question

My initial problem is that I need to implement a very fast, sparse array in C#. Original idea was to use a normal Dictionary and wrap it in

Answer 1

I, too, noticed that Dictionary is slow when the key is an integer. I don’t know exactly why this is the case, but I wrote a faster hash-table implementation for uint and ulong keys:

• Efficient32bitHashTable and Efficient64bitHashTable

Caveats/downsides:

• The 64-bit one (key is ulong) is generic, but the other one (key is uint) assumes int values because that’s all I needed at the time; I’m sure you can make this generic easily.

• Currently the capacity determines the size of the hashtable forever (i.e. it doesn’t grow).