Added delta pruning

README.md

@@ -30,8 +30,8 @@ Evaluation:
 
 ## Changelogs: <br>
 ### 0.x: <br>
-0.24: Added punishments for minor pieces in front of pawns. <br>
-0.23: Added king safety to evaluation (pawn shield and punish open files near king). Elo gain: ~-20. <br>
+0.24: Added punishments for minor pieces in front of pawns. Added delta pruning. Elo gain: ~40. <br>
+0.23: Added king safety to evaluation (pawn shield and punish open files near king). <br>
 0.22: Improved time management (tested on Lichess). Slight speed boost. <br>
 0.21: Slight speed boost. <br>
 0.2: Fixed crash. Improved tapered eval. Elo gain: ~270. <br>
@@ -41,7 +41,9 @@ Evaluation:
 ## To-do list:
 - Pawn / bishop interaction
 - Pawn storm
+- Add aspiration windows
 - Additional VICE features 
+- Optimise movegen
 
 ## Bugs to fix:
 - Doesn't castle in some positions where O-O is superior

Source/Engine/evaluate.c

@@ -11,6 +11,9 @@
 // Pos3 (fried liver) [0.0 Na5]: r1bqkb1r/ppp2ppp/2n2n2/3Pp1N1/2B5/8/PPPP1PPP/RNBQK2R b KQkq - 0 5
 // Pos4 (king safety test): r1bqkbnr/pp1p1p1p/2n1p3/2p3p1/4P3/3B1N2/PPPP1PPP/RNBQ1RK1 w kq - 0 5
 
+// Pos5 (h6 blunders): 8/8/6R1/5ppP/5k2/3r1P2/8/6K1 w - - 9 57
+// Pos6 
+
 // Temporary hack. Scales down the eval in case it's too high (assuming the code works fine)
 // #define squishFactor 0.35
 
@@ -172,6 +175,10 @@ const int KingEgTable[64] = {
   -74,  -35,  -18,  -18,  -11,   15,    4,  -17
 };
 
+/********************************
+***** Evaluation components *****
+********************************/
+
 // Applying gamePhase at startpos
 #define openingPhase 64
 
@@ -356,6 +363,10 @@ double kingSafetyScore(const S_BOARD *pos, uint8_t sq, uint8_t col, uint16_t mat
 // Used for some sort of king eval tapering. Probably not very good, but an interesting approach. Kept for legacy
 // #define ENDGAME_MAT (1 * PieceVal[wR] + 2 * PieceVal[wN] + 2 * PieceVal[wP] + PieceVal[wK])
 
+/********************************
+*** Main Evaluation Function ****
+********************************/
+
 // Evaluation function
 inline int EvalPosition(const S_BOARD *pos) {
 
@@ -445,7 +456,6 @@ inline int EvalPosition(const S_BOARD *pos) {
 		ASSERT(SQ64(sq)>=0 && SQ64(sq)<=63);
 		score += KnightMgTable[SQ64(sq)] * weight + KnightEgTable[SQ64(sq)] * ( 1 - weight );
 
-
 		// Punish knights in front of c-pawn
 		U64 mask = pos->pawns[WHITE] & FileBBMask[FilesBrd[sq]];
 		int pawnSq = PopBit(&mask);
@@ -498,7 +508,7 @@ inline int EvalPosition(const S_BOARD *pos) {
 		ASSERT(SqOnBoard(sq));
 		ASSERT(MIRROR64(SQ64(sq))>=0 && MIRROR64(SQ64(sq))<=63);
 		score -= BishopMgTable[MIRROR64(SQ64(sq))] * weight + BishopEgTable[MIRROR64(SQ64(sq))] * ( 1 - weight );
-
+		
 		// Punish bishops in front of e- or d-pawn
 		U64 mask = pos->pawns[BLACK] & FileBBMask[FilesBrd[sq]];
 		int pawnSq = PopBit(&mask);

Source/Engine/search.c

@@ -97,18 +97,27 @@ static int Quiescence(int alpha, int beta, S_BOARD *pos, S_SEARCHINFO *info) {
 		return EvalPosition(pos);
 	}
 
-	int Score = EvalPosition(pos);
+	int Score = EvalPosition(pos); // stand-pat score
 
 	ASSERT(Score>-INFINITE && Score<INFINITE);
 
+	// Beta cutoff
 	if(Score >= beta) {
 		return beta;
 	}
 
+	// Delta pruning
+	uint16_t delta = 1025; // arbitrarily large value (queen mg value)
+	// We stop searching if it's much lower than alpha
+	if (Score < alpha - delta) {
+		return alpha;
+	}
+
 	if(Score > alpha) {
 		alpha = Score;
 	}
 
+	// Delta pruning fails, and we have to search moves
 	S_MOVELIST list[1];
     GenerateAllCaps(pos,list);
 
@@ -328,7 +337,7 @@ void SearchPosition(S_BOARD *pos, S_SEARCHINFO *info) {
 			}
 			if(info->GAME_MODE == UCIMODE || info->POST_THINKING == TRUE) {
 				pvMoves = GetPvLine(currentDepth, pos);
-				if(!info->GAME_MODE == XBOARDMODE) {
+				if((!info->GAME_MODE) == XBOARDMODE) {
 					printf("pv");
 				}
 				for(pvNum = 0; pvNum < pvMoves; ++pvNum) {