/// <summary>
/// Alpha Beta pruning function.
/// </summary>
/// <param name="board"> Chess board</param>
/// <param name="ePlayer"> Color doing the move</param>
/// <param name="iDepth"> Actual search depth</param>
/// <param name="iAlpha"> Alpha limit</param>
/// <param name="iBeta"> Beta limit</param>
/// <param name="iWhiteMoveCount"> Number of moves white can do</param>
/// <param name="iBlackMoveCount"> Number of moves black can do</param>
/// <param name="abInfo"> Supplemental information</param>
/// <returns>
/// Points to give for this move or Int32.MinValue for timed out
/// </returns>
private int AlphaBeta(ChessBoard board,
ChessBoard.PlayerE ePlayer,
int iDepth,
int iAlpha,
int iBeta,
int iWhiteMoveCount,
int iBlackMoveCount,
AlphaBetaInfo abInfo)
{
int iRetVal;
List <Move> moveList;
int iPts;
int iMoveCount;
ChessBoard.PosInfoS posInfo;
TransEntryTypeE eType = TransEntryTypeE.Alpha;
ChessBoard.BoardStateMaskE eBoardExtraInfo;
ChessBoard.RepeatResultE eResult;
if (abInfo.m_dtTimeOut != DateTime.MaxValue && DateTime.Now >= abInfo.m_dtTimeOut)
{
iRetVal = Int32.MinValue; // Time out!
}
else if (board.IsEnoughPieceForCheckMate())
{
eBoardExtraInfo = board.ComputeBoardExtraInfo(ePlayer, true);
iRetVal = (abInfo.m_transTable != null) ? abInfo.m_transTable.ProbeEntry(board.CurrentZobristKey, eBoardExtraInfo, iDepth, iAlpha, iBeta) : Int32.MaxValue;
if (iRetVal == Int32.MaxValue)
{
if (iDepth == 0 || m_bCancelSearch)
{
iRetVal = board.Points(abInfo.m_searchMode, ePlayer, abInfo.m_iMaxDepth - iDepth, iWhiteMoveCount - iBlackMoveCount, abInfo.m_posInfoWhite, abInfo.m_posInfoBlack);
if (ePlayer == ChessBoard.PlayerE.Black)
{
iRetVal = -iRetVal;
}
abInfo.m_iPermCount++;
if (abInfo.m_transTable != null)
{
abInfo.m_transTable.RecordEntry(board.CurrentZobristKey, eBoardExtraInfo, iDepth, iRetVal, TransEntryTypeE.Exact);
}
}
else
{
moveList = board.EnumMoveList(ePlayer, true, out posInfo);
iMoveCount = moveList.Count;
if (ePlayer == ChessBoard.PlayerE.White)
{
iWhiteMoveCount = iMoveCount;
abInfo.m_posInfoWhite = posInfo;
}
else
{
iBlackMoveCount = iMoveCount;
abInfo.m_posInfoBlack = posInfo;
}
if (iMoveCount == 0)
{
if (board.IsCheck(ePlayer))
{
iRetVal = -1000000 - iDepth;
}
else
{
iRetVal = 0; // Draw
}
if (abInfo.m_transTable != null)
{
abInfo.m_transTable.RecordEntry(board.CurrentZobristKey, eBoardExtraInfo, iDepth, iRetVal, TransEntryTypeE.Exact);
}
}
else
{
iRetVal = iAlpha;
foreach (Move move in moveList)
{
eResult = board.DoMoveNoLog(move);
abInfo.m_arrMove[iDepth - 1] = move;
if (eResult == ChessBoard.RepeatResultE.NoRepeat)
{
iPts = -AlphaBeta(board,
(ePlayer == ChessBoard.PlayerE.Black) ? ChessBoard.PlayerE.White : ChessBoard.PlayerE.Black,
iDepth - 1,
-iBeta,
-iRetVal,
iWhiteMoveCount,
iBlackMoveCount,
abInfo);
}
else
{
iPts = 0;
}
board.UndoMoveNoLog(move);
if (iPts == Int32.MinValue)
{
iRetVal = iPts;
break;
}
else
{
if (iPts > iRetVal)
{
iRetVal = iPts;
eType = TransEntryTypeE.Exact;
}
if (iRetVal >= iBeta)
{
iRetVal = iBeta;
eType = TransEntryTypeE.Beta;
break;
}
}
}
if (abInfo.m_transTable != null && iRetVal != Int32.MinValue)
{
abInfo.m_transTable.RecordEntry(board.CurrentZobristKey, eBoardExtraInfo, iDepth, iRetVal, eType);
}
}
}
}
}
else
{
iRetVal = 0;
}
return(iRetVal);
}
/// <summary>
/// Record a new entry in the table
/// </summary>
/// <param name="i64ZobristKey"> Zobrist key. Probably unique for this board position.</param>
/// <param name="eExtraInfo"> Extra information about the board not contains in the Zobrist key</param>
/// <param name="iDepth"> Current depth (reverse)</param>
/// <param name="iValue"> Board evaluation</param>
/// <param name="eType"> Type of the entry</param>
public void RecordEntry(long i64ZobristKey, ChessBoard.BoardStateMaskE eExtraInfo, int iDepth, int iValue, TransEntryTypeE eType)
{
TransEntry entry;
i64ZobristKey ^= (int)eExtraInfo;
entry.m_i64Key = i64ZobristKey;
entry.m_iGen = m_iGen;
entry.m_eExtraInfo = eExtraInfo;
entry.m_iDepth = iDepth;
entry.m_iValue = iValue;
entry.m_eType = eType;
m_arrTransEntry[(UInt64)i64ZobristKey % (UInt64)m_arrTransEntry.Length] = entry;
}
/// <summary>
/// Record a new entry in the table
/// </summary>
/// <param name="i64ZobristKey"> Zobrist key. Probably unique for this board position.</param>
/// <param name="eExtraInfo"> Extra information about the board not contains in the Zobrist key</param>
/// <param name="iDepth"> Current depth (reverse)</param>
/// <param name="iValue"> Board evaluation</param>
/// <param name="eType"> Type of the entry</param>
public void RecordEntry(long i64ZobristKey, ChessBoard.BoardStateMaskE eExtraInfo, int iDepth, int iValue, TransEntryTypeE eType) {
TransEntry entry;
i64ZobristKey ^= (int)eExtraInfo;
entry.m_i64Key = i64ZobristKey;
entry.m_iGen = m_iGen;
entry.m_eExtraInfo = eExtraInfo;
entry.m_iDepth = iDepth;
entry.m_iValue = iValue;
entry.m_eType = eType;
m_arrTransEntry[(UInt64)i64ZobristKey % (UInt64)m_arrTransEntry.Length] = entry;
}
