Hi,
the discussion so far did omit one specific aspect. When comparing two
implementations for a switch, you have to compare the full code. For the hash
you have to include the code to calculate the hash function. This might be more
code than a simple tree lookup.
The example function:
>public int hash32shift(int key)
>{
> key = ~key + (key << 15); // key = (key << 15) - key - 1;
> key = key ^ (key >>> 12);
> key = key + (key << 2);
> key = key ^ (key >>> 4);
> key = key * 2057; // key = (key + (key << 3)) + (key << 11);
> key = key ^ (key >>> 16);
> return key;
>}
has 12 operations. Add a table and verification you get to about 18. That is
worse than a tree search with 9 levels. So for all switches with less than 512
elements, the hash is not faster.
Erwin
