Author: Dann Corbit
Date: 14:03:47 04/16/04
Considering files like this one: ftp://ftp.cis.uab.edu/pub/hyatt/TB/tbs/kqqqkr.tbs I think we can make a more compact bitbase representation. The only really interesting positions are where the dominant side does not dominate. From the above file, that boils down to this set: wtm: Lost in 0: 14415 wtm: Lost in 1: 5898 wtm: Lost in 2: 3397 wtm: Lost in 3: 1730 wtm: Draws: 52698 btm: Draws: 495121 btm: Mate in 4: 12110 btm: Mate in 3: 31861 btm: Mate in 2: 53435 btm: Mate in 1: 123889 A total of 794,554 positions in this case. I think a way to encode that set in a very compact way will be to create a perfect hash for just those positions and publish the function. (20 bits is all that are needed and 800K entries at that size for a total of about 3 MB). Another possibility would be to have two bit vectors (one for losses and one for draws). The nice thing about the bit vectors in a really sparse set is that they would RLL compress a huge amount.
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