Search found 17043 matches

by bob
Thu May 07, 2020 5:19 pm
Forum: Computer Chess Club: General Topics
Topic: test the intelligence of your engine
Replies: 9
Views: 743

Re: test the intelligence of your engine

The test is absolutely stupid. Stockfish OF COURSE sees immediately that all moves lead to immediate stalemate, as would any decent engine. But it has no wasteful stop condition and just goes to max depth before exiting. Wasteful, because on positions with play left, making the test wastes CPU time...
by bob
Tue May 05, 2020 5:57 pm
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

Do ALL threads sit at the "same table" when accessing (say) the transposition/refutation table (hash table)? If so this would really seem to slow things down. Suppose one of them is in the q-search and doesn't even want to access the thing? Or suppose it does, but at a later time after the others ha...
by bob
Sun May 03, 2020 7:55 pm
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

I don't see how that can solve the problem. You say "always access the TT in the same order". Take two threads, A and B. If they access at the same time, you can certainly make it A then B. But what if B does a probe and A has not gotten there yet. In fact, you don't even know that A will EVER get t...
by bob
Sat May 02, 2020 1:27 am
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

I didn't think anything Joshua wrote was complaining. He seemed to be interested in what was going on and could not understand the odd behavior the transposition table causes (not to mention move ordering can also change which affects LMR/LMP as well. - history counters and such.) This is one of the...
by bob
Wed Apr 29, 2020 4:57 pm
Forum: Computer Chess Club: General Topics
Topic: Syzygy Tablebases Bug
Replies: 14
Views: 2025

Re: Syzygy Tablebases Bug

Is there a documented Syzygy Tablebase bug, using the Fritz 17 GUI, where the game is drawn and the engine resigns? I have lots of games where Stockfish development engines just resigns instead of getting a draw, I just ticked the Never Resigns option on the GUI but will this work when a Play Chess...
by bob
Wed Apr 29, 2020 4:53 pm
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

Why have multiple threads accessing the same data at the same time Because shared data in the hashtable is how the worker threads exchange data! If you synchronise, that will be so slow that you could as well just go back to a single thread. If each thread gets its own separate hash table, then the...
by bob
Wed Apr 29, 2020 4:45 pm
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

Your questions at the top. Hash table is the problem. 1, 2 or more threads can store and read the same position. That's called a race condition. If you synchronize there it becomes a huge bottleneck. There are other things that need to be read and written by different threads at the same time. Pawn...
by bob
Tue Apr 28, 2020 9:25 pm
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

Your questions at the top. Hash table is the problem. 1, 2 or more threads can store and read the same position. That's called a race condition. If you synchronize there it becomes a huge bottleneck. There are other things that need to be read and written by different threads at the same time. Pawn ...
by bob
Tue Apr 28, 2020 4:15 am
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

Right. Believe me, there really is NO solution to this, if the goal is to have the parallel program run faster than the serial program. Painful but true. You can try any parallel chess program you can get your hands on, and see the same non-deterministic behavior.
by bob
Sun Apr 26, 2020 6:00 pm
Forum: Computer Chess Club: Programming and Technical Discussions
Topic: Crafty 25.6 search stability
Replies: 39
Views: 4417

Re: Crafty 25.6 search stability

About all you can do is allow each thread to search one move and then pause while the other threads do the same, one at a time. And in the same order. Which means no speedup at all, and would actually be slower than a normal alpha/beta search. If you try to let each thread search 2 moves at a time, ...