Cornered Bishop Fix (#325)

Bench: 3332916

ELO | 37.00 +- 12.06 (95%)
SPRT | 8.0+0.08s Threads=1 Hash=8MB
LLR | 2.95 (-2.94, 2.94) [-1.00, 4.00]
GAMES | N: 1216 W: 297 L: 168 D: 751

src/eval.c

@@ -23,6 +23,7 @@
 #include "board.h"
 #include "nn.h"
 #include "search.h"
+#include "uci.h"
 #include "util.h"
 
 const int PHASE_VALUES[6] = {0, 3, 3, 5, 10, 0};
@@ -65,13 +66,38 @@ BitBoard Threats(Board* board, int stm) {
   return threatened;
 }
 
+// Idea from SF to correct positions not in classical chess
+// https://tcec-chess.com/#div=frc4ld&game=27&season=21
+Score FRCCorneredBishop(Board* board) {
+  static const Score v = 25;
+
+  Score fix = 0;
+
+  if (getBit(PieceBB(BISHOP, WHITE), A1) && getBit(PieceBB(PAWN, WHITE), B2))
+    fix -= (3 + !!getBit(OccBB(BOTH), B3)) * v;
+
+  if (getBit(PieceBB(BISHOP, WHITE), H1) && getBit(PieceBB(PAWN, WHITE), G2))
+    fix -= (3 + !!getBit(OccBB(BOTH), G3)) * v;
+
+  if (getBit(PieceBB(BISHOP, BLACK), A8) && getBit(PieceBB(PAWN, BLACK), B7))
+    fix += (3 + !!getBit(OccBB(BOTH), B6)) * v;
+
+  if (getBit(PieceBB(BISHOP, BLACK), H8) && getBit(PieceBB(PAWN, BLACK), G7))
+    fix += (3 + !!getBit(OccBB(BOTH), G6)) * v;
+
+  return board->stm == WHITE ? fix : -fix;
+}
+
 // Main evalution method
 Score Evaluate(Board* board, ThreadData* thread) {
   SearchData* data = &thread->data;
 
   if (IsMaterialDraw(board)) return 0;
 
   int score = OutputLayer(board->accumulators[board->stm][board->ply], board->accumulators[board->xstm][board->ply]);
+
+  if (CHESS_960) score += FRCCorneredBishop(board);
+
   score += data->contempt[board->stm];
 
   int scalar = 128 + board->phase;

src/uci.c

@@ -252,7 +252,15 @@ void UCILoop() {
     } else if (!strncmp(in, "threats", 7)) {
       PrintBB(Threats(&board, board.stm));
     } else if (!strncmp(in, "eval", 4)) {
-      int score = Predict(&board);
+      board.ply = 0;
+
+      board.accumulators[WHITE] = threads->accumulators[WHITE];
+      board.accumulators[BLACK] = threads->accumulators[BLACK];
+
+      RefreshAccumulator(board.accumulators[WHITE][0], &board, WHITE);
+      RefreshAccumulator(board.accumulators[BLACK][0], &board, BLACK);
+
+      int score = Evaluate(&board, threads);
       score = board.stm == WHITE ? score : -score;
 
       for (int r = 0; r < 8; r++) {
@@ -270,8 +278,13 @@ void UCILoop() {
               printf("   %c   |", PIECE_TO_CHAR[board.squares[sq]]);
           } else if (board.squares[sq] < WHITE_KING) {
             popBit(board.occupancies[BOTH], sq);
-            int new = Predict(&board);
+
+            RefreshAccumulator(board.accumulators[WHITE][0], &board, WHITE);
+            RefreshAccumulator(board.accumulators[BLACK][0], &board, BLACK);
+
+            int new = Evaluate(&board, threads);
             new = board.stm == WHITE ? new : -new;
+
             int diff = score - new;
             printf("%+7d|", diff);
             setBit(board.occupancies[BOTH], sq);