Not for my particular encoding, as I have "10" to indicate a terminal node and "11" to indicate a non-terminal. Essentially it's a 3-valued encoding of 'empty', 'terminal', 'nonterminal' for a variable number of children.

AND your input with 0xAAAAAAAA (ie 101010...10 binary) to turn all the "11" values into "10".

How does help me use popcnt to find how many bit pairs are used and how many are empty? Edit: whoops, I gotcha.

I'll profile this.

Edit 2: no I won't profile it, because I don't have the instruction. Damn.

You don't need to have POPCNT to implement much faster bit counting:

http://graphics.stanford.edu/~seander/bithacks.html#CountBit...