public Eval Search(Draft wDraft, Eval mAlpha, Eval mBeta,
Move moveExcluded = Move.Undefined) {
var moves = PseudoMoves;
BestMoves.Clear(); //[Required]
#region Test for Draw
if (IsDraw()) { //[Note]setDraw50() must be called after tryMove(), below.
State.IncEvalType(EvalType.Exact);
return eval();
}
#endregion
#region Test for entry into Quiet Search
var bInCheck = InCheck();
if (bInCheck) { // Check Extension
if (extended(ref wDraft, SearchExtensions.Check))
AtomicIncrement(ref State.CheckExtCount);
}
//
// Depth is tested here, rather than in the PVS recursion case,
// because search also recurses from the heuristic cases below.
//
var wDepth = depth(wDraft); // InCheck Adjusted Depth
if (wDepth < 1) {
#if Quiescence
return quiet(mAlpha, mBeta);
#else
return boundValue(eval(), mAlpha, mBeta);
#endif
}
#endregion
#region Transposition Table Lookup
#if TraceVal
var bTrace = IsTrace();
if (IsTrace()) { //[Note]CurrentMove Undefined
Display($"Search(Depth = {wDepth})");
}
#endif
Debug.Assert(mAlpha < mBeta, "Alpha must be less than Beta");
var goodMoves = new List<GoodMove>(nFirstCapacity);
var bFoundValue = probeXP(wDepth, mAlpha, mBeta, moveExcluded, goodMoves,
out Move moveFound, out Eval mValueFound, out EvalType etFound);
// Variations updated iff bFoundValue
if (bFoundValue) {
// moveFound not always defined for EvalType.Upper [Fail Low]
if (isDefinite(moveFound)) { //[Safe]Also prevent unexpected EmptyMove
#if DebugMove
unpackMove1(moveFound, out sq sqFrom, out sq sqTo, out Piece piece, out Piece promotion, out Boolean bCapture);
//unpackMove2(moveFound, out sq sqFrom, out sq sqTo, out Piece piece, out Piece promotion, out Piece capture, out Boolean bCastles, out Boolean bCapture);
#endif
if (IsMovePosition) // Pass empty BestMoves, at top level
AddPV(mAlpha, mValueFound, moveFound, BestMoves);
#if AddBestMoves
BestMoves.Add(moveFound); // Safe to update BestMoves now
#endif
}
return mValueFound;
}
#endregion
#region Heuristic Tests
var bReduced = (FlagsMode & ModeFlags.Reduced) != 0;
if (bReduced)
AtomicIncrement(ref State.ReducedTotal);
var bTestSingular = false;
var bPruneQuiet = false;
var bPVS = (FlagsMode & ModeFlags.ZWS) == 0;
var bMoveExcluded = isDefined(moveExcluded);
var wReducedDraft = reduceShallow(wDraft);// Draft for Heuristic Searches
if (!bInCheck) {
var mStand = standpatval(mValueFound, etFound);
if (!bPVS) {
if (prune(wDraft, wDepth, mAlpha, mBeta, mValueFound, etFound, bMoveExcluded, out Eval mPrunedValue))
return mPrunedValue;
}
if (!bReduced) {
//[Conditional]
threat(ref wDraft, ref wReducedDraft, ref wDepth);
}
// Determine whether Futility Pruning should be performed at Frontier Nodes:
if (State.IsFutility && 0 < wDepth) {
var bNonMateWindow = -MateMin < mAlpha && mBeta < MateMin;
var bNonEndGame = (FlagsEG & EGFlags.EndGame) == 0;
if (bNonMateWindow && bNonEndGame) {
var nMargin = wDepth - 1;
if (nMargin < FutilityMargin.Length)
bPruneQuiet = mStand + FutilityMargin[nMargin] <= mAlpha;
}
} // Futility Pruning
#if SingularExtension
bTestSingular = wSingularDepthMin <= wDepth &&
EvalUndefined < mValueFound &&
//[Test]More inclusion performs better than less!
Abs(mValueFound) < mQueenWeight &&
isDefined(moveFound) && !(bReduced || bMoveExcluded) &&
canExtend(vSingular); //[Ergo]child.canExtend(vSingular) below
#endif
} // !bInCheck
#endregion
#region Generate Moves
//
// The "go searchmoves" UCI command sets SearchMoves
// to restrict the set of candidate moves at the Root:
//
if (SearchMoves is not null && SearchMoves.Count > 0) {
moves.Clear();
moves.AddRange(SearchMoves);
#if DebugSearchMoves
var sb = new StringBuilder("SearchMoves:");
sb.MapMoves(Extension.AppendPACN, moves, State.Rule);
LogLine(sb.ToString());
#endif
}
protected Eval quiet(Eval mAlpha, Eval mBeta)
{
var moves = PseudoMoves;
BestMoves.Clear(); //[Required]
#region Test for Draw
if (IsDraw()) //[Note]setDraw50() will not be called below
{
State.IncEvalType(EvalType.Exact);
#if TransposeQuiet
return(eval());
#else
return(boundValue(eval(), mAlpha, mBeta));
#endif
}
#endregion
#region Transposition Table Lookup
#if TraceVal
var bTrace = IsTrace();
if (bTrace)
{
const String sLabel = "quiet()";
Display(sLabel); //[Note]Undefined CurrentMove
}
#endif
// BestMoves updated iff bFoundValue
if (probeQxnt(mAlpha, mBeta, out Move moveFound, out Eval mValueFound, out EvalType etFound))
{
// moveFound not always defined for EvalType.Upper [Fail Low]
if (isDefinite(moveFound)) //[Safe]Also prevent unexpected EmptyMove
{
#if DebugMove
unpackMove1(moveFound, out sq sqFrom, out sq sqTo, out Piece piece, out Piece promotion, out Boolean bCapture);
//unpackMove2(moveFound, out sq sqFrom, out sq sqTo, out Piece piece, out Piece promotion, out Piece capture, out Boolean bCastles, out Boolean bCapture);
#endif
#if AddBestMoves
BestMoves.Add(moveFound);
#endif
}
return(mValueFound);
}
#endregion
#region Move Loop Initializaton
#if QuietCheck || QuietMate
var bInCheck = InCheck();
#endif
var et = EvalType.Upper; //[Init]Fail Low is the default assumption
// Stand Pat (tests Draw Flags)
var mStand = standpatval(mValueFound, etFound);
var moveBest = Move.Undefined; //[Init]
var mValue = EvalUndefined;
var mBest = EvalUndefined;
var bStandPat = mAlpha /*+ mStandPatWeight*/ < mStand;
if (bStandPat)
{
mBest = mStand;
if (mAlpha < mBest)
{
mAlpha = mBest;
}
}
#endregion
if (mBeta <= mAlpha)
{
//[Test]return boundValue(mBest, mAlpha, mBeta);
}
else
{
#region Generate Moves
if (SearchMoves is not null && SearchMoves.Count > 0)
{
moves.Clear();
moves.AddRange(SearchMoves);
#if DebugSearchMoves
var sb = new StringBuilder("SearchMoves:");
sb.MapMoves(Extension.AppendPACN, moves, State.Rule);
sb.FlushLine();
#endif
}