Arasan 21.0

[jdart]

Arasan 21.0 is available from: https://www.arasanchess.org. On top of the beta version released a short time ago, it has some scoring changes, code cleanup, a fix in the Winboard "memory" command, and some book updates.

Changes in Arasan 21.0:

1) Implement LazySMP instead of YBWC for multi-threading (major re-structuring).
2) Stricter/earlier validity checking on hash move.
3) When failing low with a mate score, widen the aspiration window all
the way to -Mate1. Fixes Github issue #16.
4) Improvements to time management. When failing low, extend time based on
how bad & how recent the fail low(s) were. When failing high, extend
time but less than for a fail-low.
5) When storing a hash entry that is an eval score, store the hash move
also, if there is one. Remove an unnecessary test in qsearch.
6) In Winboard mode, send a response to "ping" immediately when pondering.
7) Fix regression in "go searchmoves" command (Github issue #17).
8) Reset search status (by calling "new" internally) after receiving
"result." Fixes issues when running matches offline under xboard,
which may start a new game w/o sending "new."
9) Fixes to Winboard edit mode.
10) Don't resign lost tb positions unless far behind in material.
11) Apply filtering to root moves before forced move detection. Change
forced move logic - terminate even if failing high/low.
12) Simplify outpost scoring.
13) Add scoring terms to encourage own piece proximity to King when King is
under attack.
14) Changes to book move selection logic and associated options.
15) Fix a possible bug in handling of weight comments in makebook utility.
16) Fix output of objective value from tuner. Bug fix in scaling of gradient -
makes convergence faster.
17) Increase probcut min depth.
18) Fixes to Winboard "memory" command.
19) Quite a bit of code cleanup and conversion to C++11 style. Add some unit
tests.

This version in my testing is measurably, but not a lot, stronger than 20.5 single-threaded. Multithreaded performance should be quite a bit better due to LazySMP.

--Jon

[Graham Banks]

Multi-CPU results should be interesting.

[cdani]

Nice! Congratulations. Will be specially interesting to see lazy smp results.