int SearchCut(int alpha, int beta, int depth, int height, int mate_threat, bool allowNull = true)
{
beta = Math.Min(beta, G.MATE - height);
if (depth <= 0)
{
if (stepList[stepList.Count - 1].move.checking)
{
//被照将时，推迟进入静态搜索
depth++;
}
else
{
return(SearchQuiesce(alpha, beta, 0, height));
}
}
stat.ZeroWindowNodes++;
int best = HarmlessPruning(height);
if (best >= beta)
{
return(best);
}
#if USE_HASH
HashStruct t = TT.ReadHash(Key);
if (t.Move.sqSrc == 0)
{
TransKiller = null;
}
else
{
if (t.AlphaDepth >= depth)
{
if (t.Alpha <= alpha)
{
return(t.Alpha);
}
}
if (t.BetaDepth >= depth)
{
if (t.Beta >= beta)
{
return(t.Beta);
}
}
if (t.Alpha == t.Beta)
{
return(t.Alpha);
}
TransKiller = t.Move;
TransKiller.pcSrc = pcSquares[TransKiller.sqSrc];
TransKiller.pcDst = pcSquares[TransKiller.sqDst];
}
#endif
Debug.Assert(height < G.MAX_PLY);
MOVE lastMove = stepList[stepList.Count - 1].move;
#if NULL_MOVE
if (allowNull && depth >= G.NullDepth)
{
//for any opponent pure loss and bad capture, it's better to take it and see the accurate score
//for any opponent good capture, we are already so bad, it makes no sense to do null move
//for those equal material exchange, we must finish recapture
//for mating and checking moves, we can not skip the moves
if (!lastMove.checking && lastMove.score > HistoryScore && lastMove.score < GoodScore && lastMove.pcDst == 0 && Math.Abs(beta) < G.WIN)
{
MakeNullMove();
int vl = -SearchCut(-beta, -alpha, depth - G.NullReduction - 1, height + 1, mate_threat, false);
UnmakeNullMove();
#if NULL_VERIFICATION
if (depth > G.VerReduction && vl >= beta)
{
vl = SearchCut(beta, depth - G.VerReduction, height + 1, false);
}
#endif
if (vl >= beta)
{
Debug.Assert(vl < G.WIN); // do not return unproven mates
TT.WriteHash(Key, G.HASH_BETA, vl, depth, new MOVE());
stat.NullCutoffs++;
return(vl);
}
}
}
#endif
IEnumerable <MOVE> moves = GetNextMove(7, height, mate_threat);
MOVE mvBest = new MOVE();
int opt_value = G.MATE;
List <MOVE> mvPlayed = new List <MOVE>();
foreach (MOVE mv in moves)
{
int new_depth = depth - 1;
if (mv.checking)
{
new_depth++;
}
if (mate_threat < 0)
{
if (best < -G.WIN && mvPlayed.Count > 0)
{
mate_threat = height;
alpha = -G.WIN;
}
}
else
{
MOVE matekiller = Killers[mate_threat + 1, 0];
if (mv == matekiller || mate_threat == height && best > -G.WIN || !IsLegalMove(matekiller.sqSrc, matekiller.sqDst))
{
mate_threat = -1;
}
}
#if HISTORY_PRUNING
bool reduced = false;
if (depth >= G.HistoryDepth && !lastMove.checking && new_depth < depth && mvPlayed.Count >= G.HistoryMoveNb)
{
int k = GetHistoryIndex(mv);
if ((float)(HistHit[k]) / HistTotal[k] < 0.6)
{
new_depth--;
reduced = true;
stat.HistoryReduced++;
}
}
#endif
#if FUTILITY_PRUNING
if (depth == 1 && !lastMove.checking && !mv.checking && new_depth == 0 && mv.pcDst == 0)
{
if (opt_value == G.MATE)
{
opt_value = Simple_Evaluate() + G.FutilityMargin;
}
if (opt_value < beta)
{
continue;
}
}
#endif
//if the opponent is delaying mate by checking, do not enter quiesce until the mate killer move is tried
if (new_depth == 0 && mate_threat > 0)
{
new_depth = 1;
}
Debug.Write(new string('\t', height));
Debug.WriteLine($"{mv} {alpha}, {beta}, {best} {mv.killer}");
MakeMove(mv, false);
int vl;
//to avoid quiesce search beta cut off too early, use -best instead of -alpha as new beta
if (new_depth == 0 && alpha < G.WIN)
{
vl = -SearchCut(-beta, -best, 0, height + 1, mate_threat);
}
else
{
vl = -SearchCut(-beta, -alpha, new_depth, height + 1, mate_threat);
}
#if HISTORY_PRUNING
if (vl >= beta && reduced)
{
new_depth++;
vl = -SearchCut(-beta, -alpha, new_depth, height + 1, mate_threat);
stat.HistoryResearched++;
}
#endif
UnmakeMove();
if (vl > best)
{
best = vl;
mvBest = mv;
if (vl >= beta)
{
SetBestMove(mvBest, best, depth, height);
foreach (MOVE m1 in mvPlayed)
{
HistoryBad(m1);
}
#if USE_HASH
TT.WriteHash(Key, G.HASH_BETA, best, depth, mvBest);
#endif
stat.BetaCutoffs++;
return(vl);
}
if (vl > alpha)
{
alpha = vl;
}
}
mvPlayed.Add(mv);
}
#if USE_HASH
TT.WriteHash(Key, G.HASH_ALPHA, best, depth, mvBest);
#endif
return(best);
}
int SearchPV(int alpha, int beta, int depth, int height, out List <MOVE> pvs)
{
beta = Math.Min(beta, G.MATE - height);
pvs = new List <MOVE>();
if (depth <= 0)
{
if (stepList[stepList.Count - 1].move.checking)
{
//被照将时，推迟进入静态搜索
depth++;
}
else
{
return(SearchQuiesce(alpha, beta, 0, height));
}
}
stat.PVNodes++;
int best = HarmlessPruning(height);
//distance pruning
if (best >= beta)
{
return(best);
}
MOVE mvBest = new MOVE();
int hashFlag = 0;
List <MOVE> subpv = null;
TransKiller = null;
#if USE_HASH
HashStruct t = TT.ReadHash(Key);
if (t.Move.sqSrc == 0)
{
TransKiller = null;
}
else
{
if (t.AlphaDepth >= depth)
{
if (t.Alpha <= alpha)
{
return(t.Alpha);
}
}
if (t.BetaDepth >= depth)
{
if (t.Beta >= beta)
{
return(t.Beta);
}
}
TransKiller = t.Move;
TransKiller.pcSrc = pcSquares[TransKiller.sqSrc];
TransKiller.pcDst = pcSquares[TransKiller.sqDst];
}
#endif
#if INTERNAL_ITERATIVE_DEEPENING
if (depth >= G.IIDDepth && TransKiller is null)
{
int new_depth = depth - G.IIDReduction;
Debug.Assert(new_depth > 0);
int vl = SearchPV(alpha, beta, new_depth, height, out subpv);
if (vl < alpha)
{
vl = SearchPV(-G.MATE, beta, new_depth, height, out subpv);
}
if (subpv.Count > 0)
{
TransKiller = subpv[0];
}
}
#endif
IEnumerable <MOVE> moves = GetNextMove(7, height);
foreach (MOVE mv in moves)
{
Debug.Write(new string('\t', height));
Debug.WriteLine($"{mv} {alpha}, {beta}, {best},{mv.killer}");
int new_depth = depth - 1;
if (mv.sqDst == stepList[stepList.Count - 1].move.sqDst && mv.score > 0 ||
mv.checking)
{
new_depth++;
}
MakeMove(mv, false);
int vl;
if (mvBest.sqSrc == 0)
{
vl = -SearchPV(-beta, -alpha, new_depth, height + 1, out subpv);
}
else
{
//当depth == 0, 且best < alpha时，传给quiesce的beta用 -best代替 -alpha，可以避免eval() > beta过早返回。
//返回的值和最佳着法只是因为搜索深度浅而貌似高于best。后续重新搜索时这个非最佳着法被首先搜索，降低了效率。
if (new_depth == 0 && alpha < G.WIN)
{
vl = -SearchCut(-alpha - 1, -best, new_depth, height + 1, -1);
}
else
{
vl = -SearchCut(-alpha - 1, -alpha, new_depth, height + 1, -1);
}
if (vl > alpha) // && vl < beta
{
Debug.WriteLine("Re-search");
Debug.Write(new string('\t', height));
Debug.WriteLine($"{mv} {alpha}, {beta}, {vl}");
vl = -SearchPV(-beta, -vl, new_depth, height + 1, out subpv);
stat.PVChanged++;
}
}
UnmakeMove();
if (vl > best)
{
best = vl;
if (vl >= beta)
{
stat.BetaCutoffs++;
mvBest = mv;
hashFlag = G.HASH_BETA;
break;
}
if (vl > alpha)
{
alpha = vl;
mvBest = mv;
hashFlag = G.HASH_PV;
pvs.Clear();
pvs.Add(mv);
pvs.AddRange(subpv);
}
}
else
{
HistoryBad(mv);
}
}
if (best > -G.WIN)
{
#if USE_HASH
TT.WriteHash(Key, hashFlag, best, depth, mvBest);
#endif
if (mvBest.pcSrc != 0)
{
SetBestMove(mvBest, best, depth, height);
}
}
return(best);
}