MadChess 3.0 Beta 42d7702 (Position Cache Optimization)

Quoting from my Pull Request #12:

Converted Cache class’ _positions field from a jagged array to a flat array. The flat array is more memory efficient than a jagged array. Jagged arrays have a .NET object header for each sub-array (for garbage collection tracking of reachable-from-root). This enables more positions to be stored per megabyte of memory. The code in this PR stores 65,536 positions per MB = 8,388,608 positions for a typically sized 128 MB cache.

Added stats to track cache hit %, best move found in cached position %, and count of invalid best moves. Stats are displayed when the debug on command is sent.

Experimented condensing CachedPosition struct from two ulongs to a single ulong. Only 15 bits were available for a partial key. Testing showed the partial key caused too many invalid best moves to be extracted from cached positions. Performed weaker than leaving CachedPosition as a struct with a full key.

Here’s my implementation of the Cache class.

Here’s my implementation of the associated CachedPosition struct and CachedPositionData static class.

This improved cache code increased the playing strength of MadChess 3.0 Beta by 8 Elo.

1. GitHub commit (hash) or Subversion source code revision (integer)
2. Win At Chess position test, 3 seconds per position
3. Bullet chess, 2 min / game + 1 sec / move