RFR (M) 8059461: Refactor IndexSet for better performance (preliminary)

[John Rose]

On Nov 5, 2014, at 1:26 PM, Aleksey Shipilev <aleksey.shipilev at oracle.com> wrote:

>  - IndexSetIterator performance is important, and therefore the lookup
> table approach from IndexSetIterator was transplanted to new
> BitMapIterator. We might want to improve BitMap::get_next_one_offset
> with lookup tables as well, but that will contaminate the current
> experiment.

Curiously, I googled around for info on bitset enumeration, and found the mother lode here:
  http://chessprogramming.wikispaces.com/BitScan

It seems the table-based algorithm is still quite competitive, even with hardware supported ffs/ctz.

— John
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