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Stockfish Questions
Posted: Sat Feb 28, 2015 5:46 pm
by vittyvirus
I was looking at SF code to get some speed ups in perft and better eval in Yaka. Some questions:
file: position. cpp, function do_move()
Code: Select all
// Update incremental score
st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
psq[us][PAWN][to]; is always zero.
file: pawns.cpp, function evaluate()
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
WHAT??? :O
Sorry if I missed something...
Re: Stockfish Questions
Posted: Sat Feb 28, 2015 8:18 pm
by mcostalba
vittyvirus wrote:I was looking at SF code to get some speed ups in perft and better eval in Yaka. Some questions:
file: position. cpp, function do_move()
Code: Select all
// Update incremental score
st->psq += psq[us][promotion][to] - psq[us][PAWN][to];
psq[us][PAWN][to]; is always zero.
Nice, thanks, good eye
vittyvirus wrote:
file: pawns.cpp, function evaluate()
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
WHAT??? :O
Sorry if I missed something...
rank_bb() expands again 'b', so you need to bitwise 'and' again ...eventually try to rewrite in a better way...if you find one
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 12:04 am
by Sven
mcostalba wrote:vittyvirus wrote:
file: pawns.cpp, function evaluate()
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
WHAT??? :O
Sorry if I missed something...
rank_bb() expands again 'b', so you need to bitwise 'and' again ...eventually try to rewrite in a better way...if you find one
This should return the same result but might be more readable (despite the bigger number of characters):
Code: Select all
Rank ourRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & ourPawns));
Rank theirRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & theirPawns));
backward = (Us == WHITE) ? (theirRank <= ourRank + 1) : (theirRank >= ourRank - 1);
as opposed to the original:
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
backward = (b | shift_bb<Up>(b)) & theirPawns;
I don't know which one is faster.
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 11:00 am
by mcostalba
Sven Schüle wrote: I don't know which one is faster.
It's faster and shorter the original
Anyhow thanks for this attempt.
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 11:06 am
by Henk
Sven Schüle wrote:mcostalba wrote:vittyvirus wrote:
file: pawns.cpp, function evaluate()
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
WHAT??? :O
Sorry if I missed something...
rank_bb() expands again 'b', so you need to bitwise 'and' again ...eventually try to rewrite in a better way...if you find one
This should return the same result but might be more readable (despite the bigger number of characters):
Code: Select all
Rank ourRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & ourPawns));
Rank theirRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & theirPawns));
backward = (Us == WHITE) ? (theirRank <= ourRank + 1) : (theirRank >= ourRank - 1);
as opposed to the original:
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
backward = (b | shift_bb<Up>(b)) & theirPawns;
I don't know which one is faster.
I don't understand anything of it. Perhaps normal english explanation would help. Even don't know what it is all about. Maybe that's why I don't study Stockfish code for it is too difficult for me to understand. Or perhaps I don't want to spend so much time on it trying to understand it.
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 11:18 am
by mcostalba
Henk wrote:
I don't understand anything of it.
That's for sure.
Henk wrote:
Perhaps normal english explanation would help.
Whay should I help you? you are just a troll pretending to be an engine author when you even didn't know what an engine is (very possibly you even don't know how to program). I don'tunderstand what's the point of posting nonsense here, if you would be interested in the subject probably you would try to mock up something, like a legal move generator, just to start, so I think you are not even interested in the subject, you post just for trolling.
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 11:30 am
by Henk
mcostalba wrote:Henk wrote:
I don't understand anything of it.
That's for sure.
Henk wrote:
Perhaps normal english explanation would help.
Whay should I help you? you are just a troll pretending to be an engine author when you even didn't know what an engine is (very possibly you even don't know how to program). I don'tunderstand what's the point of posting nonsense here, if you would be interested in the subject probably you would try to mock up something, like a legal move generator, just to start, so I think you are not even interested in the subject, you post just for trolling.
Yes and I am a liar too. Please don't waste your time on me. I also only want to talk to troll friends.
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 2:15 pm
by vittyvirus
Henk wrote:Sven Schüle wrote:mcostalba wrote:vittyvirus wrote:
file: pawns.cpp, function evaluate()
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
WHAT??? :O
Sorry if I missed something...
rank_bb() expands again 'b', so you need to bitwise 'and' again ...eventually try to rewrite in a better way...if you find one
This should return the same result but might be more readable (despite the bigger number of characters):
Code: Select all
Rank ourRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & ourPawns));
Rank theirRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & theirPawns));
backward = (Us == WHITE) ? (theirRank <= ourRank + 1) : (theirRank >= ourRank - 1);
as opposed to the original:
Code: Select all
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
backward = (b | shift_bb<Up>(b)) & theirPawns;
I don't know which one is faster.
I don't understand anything of it. Perhaps normal english explanation would help. Even don't know what it is all about. Maybe that's why I don't study Stockfish code for it is too difficult for me to understand. Or perhaps I don't want to spend so much time on it trying to understand it.
The reason why I like SF the most is because of clean code. I agree that you need some knowledge of what is being done, but not too much
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 2:30 pm
by Sven
mcostalba wrote:Sven Schüle wrote: I don't know which one is faster.
It's faster and shorter the original
Anyhow thanks for this attempt.
You may be right, but just for curiosity: how did you come to that conclusion?
"Shorter" is certainly right, even if I rename some identifiers longer than 2 chars. My argument was "better readability" which is not always equivalent to "less characters".
And "faster"? How would you explain it? I could imagine that in my proposal the first and the second line are fully independent calculations so the CPU could possibly execute the whole piece of code with less cycles. Furthermore I think it has less memory access (no need to access the RankBB array) and also less operations (the original has a couple of and/or/shift). Both are branchless (the ?: is resolved by the compiler due to "Us" being a template parameter). What would make the original faster? One more LSB/MSB operation? That is the only reason I could imagine.
This is not an important issue, for sure, since the differences are negligible and would never justify a change of the working code. I just ask to understand better your reasoning.
Re: Stockfish Questions
Posted: Sun Mar 01, 2015 5:53 pm
by mcostalba
Here is the disassembly of 2 solutions (MSVC 2013)
Code: Select all
// We now know there are no friendly pawns beside or behind this
// pawn on adjacent files. We now check whether the pawn is
// backward by looking in the forward direction on the adjacent
// files, and picking the closest pawn there.
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
000000013F7CBE22 mov r9,qword ptr [r11+rdx+2269E0h]
000000013F7CBE2A mov rax,r12
000000013F7CBE2D or rax,rsi
000000013F7CBE30 and rax,r9
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
000000013F7CBE33 bsf rax,rax
000000013F7CBE37 movsxd rcx,eax
000000013F7CBE3A sar rcx,3
000000013F7CBE3E mov rdx,qword ptr [rdx+rcx*8+13B6A0h]
000000013F7CBE46 and rdx,r9
// If we have an enemy pawn in the same or next rank, the pawn is
// backward because it cannot advance without being captured.
backward = (b | shift_bb<Up>(b)) & theirPawns;
000000013F7CBE49 movzx r9d,byte ptr [e]
000000013F7CBE4F mov rax,rdx
000000013F7CBE52 shl rax,8
000000013F7CBE56 or rax,rdx
000000013F7CBE59 test r12,rax
000000013F7CBE5C setne r12b
000000013F7CBE60 jmp `anonymous namespace'::evaluate<0>+1F5h (013F7CBE65h)
and yours:
Code: Select all
// We now know there are no friendly pawns beside or behind this
// pawn on adjacent files. We now check whether the pawn is
// backward by looking in the forward direction on the adjacent
// files, and picking the closest pawn there.
Rank ourRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & ourPawns));
000000013F7CBE25 mov rcx,qword ptr [r10+rax+2269E0h]
000000013F7CBE2D mov rax,rcx
000000013F7CBE30 and rcx,qword ptr [rsp+78h]
000000013F7CBE35 and rax,rdi
000000013F7CBE38 bsf rdx,rax
Rank theirRank = rank_of(backmost_sq(Us, pawn_attack_span(Us, s) & theirPawns));
000000013F7CBE3C bsf rax,rcx
000000013F7CBE40 sar edx,3
000000013F7CBE43 sar eax,3
backward = (Us == WHITE) ? (theirRank <= ourRank + 1) : (theirRank >= ourRank - 1);
000000013F7CBE46 inc edx
000000013F7CBE48 cmp eax,edx
000000013F7CBE4A setle bpl
000000013F7CBE4E jmp `anonymous namespace'::evaluate<0>+1E3h (013F7CBE53h)
backward = false;
000000013F7CBE50 xor bpl,bpl
Sorry I didn't do any speed test, also because you version is not functionally equivalent with original (bench signature of 7657127 instead of 8285241)