Tuesday, November 11, 2008

BikJump v2.0 released

Besides switching to a home-brewed bitboard representation, other parts of BikJump underwent refactoring as well. Some modifications turned out to modify strength negatively. I already wrote about null moves below. Furthermore, because the new bitboard move generator generates legal captures much faster than all legal moves, the quiescence search originally had been modified to look at captures only. After including checks again in the first few nodes, some bad tactical errors were avoided. Similarly, late move reduction had become too optimistic, and needed some adjustment towards the scheme used by the older BikJump.

The "perft" nodes-per-second performance (which everybody measures differently; I simply traverse the complete tree with the same move generator that is used in search, including some bookkeeping) is about 13000KNs on a 2.66GHz Core 2 Duo. The nodes-per-second of the actual search in the first Nunn position is now about 1070KNs (64-bit) and 790KNs (32-bit) on a 2.66GHz Core 2 Duo, and about 480KNs (32-bit) on a 3GHz Pentium IV processor (mainly because bitscans are much slower on this platform). In contrast v1.8 scored about, respectively, 570KNs (no difference for 32-bit and 64-bit) and 350KNs (32-bit) on these two platforms. After a few preliminary tournaments, playing strength of the new BikJump seems improved when running on a Core 2 Duo, and appears the same on the older Pentium IV processor.

Although I had really hoped for much more noticeable gains from switching to bitboards and revising the sources, I decided to release BikJump v2.0 to give it a wider exposure. The source code has become much cleaner, while occasionally the new version plays pretty decent chess. I am still hopeful, though a little less optimistic than before, to make more substantial improvements later.

Results of a Nunn test set run-the-gauntlet 4'+1'' tournament, 512MB cache, Nalimov endgame tablebases (complete 3,4,5-piece, some 6-piece), ponder on, on an Intel Core 2 Quad Q6700 2.66GHz, 8MB L2 Cache, 1066MHz FSB, 6GB RAM:


BikJump v2.0 (64-bit)
- Roce 0.0380 16.0 - 3.0 +15/-2/=2 84.21%
- Mediocre v0.332 13.0 - 7.0 +11/-5/=4 65.00%
- BikJump v1.8 (64-bit) 12.5 - 7.5 +10/-5/=5 62.50%
- Philou 2.0.0 12.5 - 7.5 +12/-7/=1 62.50%
- Monarch 1.7 11.5 - 7.5 +10/-6/=3 60.53%
- BikJump v2.0 (32-bit) 11.0 - 9.0 +5/-3/=12 55.00%
- ZCT0.3.2447 JA 6.5 - 13.5 +4/-11/=5 32.50%
- Twisted Logic 20080620 0.5 - 19.5 +0/-19/=1 2.50%
- Fritz 11 0.0 - 20.0 +0/-20/=0 0.00%