From 9331729d765fc9347f769c310f1fff4bc39fdbad Mon Sep 17 00:00:00 2001
From: Mattia Giambirtone <nocturn9x@nocturn9x.space>
Date: Sat, 11 May 2024 11:25:45 +0200
Subject: [PATCH] Add SEE to move ordering (gains 44.7 +/- 22.9)

---
 Chess/nimfish/nimfishpkg/search.nim | 51 ++++++++++++++++-------------
 1 file changed, 28 insertions(+), 23 deletions(-)

diff --git a/Chess/nimfish/nimfishpkg/search.nim b/Chess/nimfish/nimfishpkg/search.nim
index eefebfe..13762f6 100644
--- a/Chess/nimfish/nimfishpkg/search.nim
+++ b/Chess/nimfish/nimfishpkg/search.nim
@@ -81,12 +81,11 @@ const
     # higher offsets will always be placed
     # first
     TTMOVE_OFFSET = 700_000
-    MVV_LVA_OFFSET = 600_000
-    GOOD_SEE_OFFSET {.used.} = 500_000
-    KILLERS_OFFSET = 400_000
-    HISTORY_OFFSET = 300_000
-    QUIET_OFFSET = 200_000
-    BAD_SEE_OFFSET {.used.} = 100_000
+    GOOD_SEE_OFFSET = 600_000
+    KILLERS_OFFSET = 500_000
+    HISTORY_OFFSET = 400_000
+    QUIET_OFFSET = 300_000
+    BAD_SEE_OFFSET = 200_000
 
 
 func computeLMRTable: array[MAX_DEPTH, array[218, int]] {.compileTime.} =
@@ -187,7 +186,10 @@ proc getEstimatedMoveScore(self: SearchManager, move: Move, ply: int): int =
         return KILLERS_OFFSET
 
     if move.isTactical():
-        if move.isCapture():
+        let seeScore = self.board.position.see(move)
+        # We want to prioritize good captures (see > 0), but if the capture
+        # is bad then at least we sort it with MVVLVA
+        if seeScore < 0 and (move.isCapture() or move.isEnPassant()):
             # Implementation of MVVLVA: Most Valuable Victim Least Valuable Aggressor.
             # We prioritize moves that capture the most valuable pieces, and as a
             # second goal we want to use our least valuable pieces to do so (this
@@ -196,23 +198,26 @@ proc getEstimatedMoveScore(self: SearchManager, move: Move, ply: int): int =
             let capturedScore = MVV_LVA_MULTIPLIER * self.board.position.getPieceScore(move.targetSquare)
             result = capturedScore - self.board.position.getPieceScore(move.startSquare)
         
-        # If the capture is also a promotion we want to give it an even bigger bonus
-        if move.isPromotion():
-            var piece: Piece
-            case move.getPromotionType():
-                of PromoteToBishop:
-                    piece = Piece(kind: Bishop, color: sideToMove)
-                of PromoteToKnight:
-                    piece = Piece(kind: Knight, color: sideToMove)
-                of PromoteToRook:
-                    piece = Piece(kind: Rook, color: sideToMove)
-                of PromoteToQueen:
-                    piece = Piece(kind: Queen, color: sideToMove)
-                else:
-                    discard  # Unreachable
-            result += PROMOTION_MULTIPLIER * self.board.position.getPieceScore(piece, move.targetSquare)
+            # If the capture is also a promotion we want to give it an even bigger bonus
+            if move.isPromotion():
+                var piece: Piece
+                case move.getPromotionType():
+                    of PromoteToBishop:
+                        piece = Piece(kind: Bishop, color: sideToMove)
+                    of PromoteToKnight:
+                        piece = Piece(kind: Knight, color: sideToMove)
+                    of PromoteToRook:
+                        piece = Piece(kind: Rook, color: sideToMove)
+                    of PromoteToQueen:
+                        piece = Piece(kind: Queen, color: sideToMove)
+                    else:
+                        discard  # Unreachable
+                result += PROMOTION_MULTIPLIER * self.board.position.getPieceScore(piece, move.targetSquare)
 
-        return result + MVV_LVA_OFFSET
+            return result + BAD_SEE_OFFSET
+        else:
+            # If the capture is good then we just use the SEE score + the offset
+            return seeScore + GOOD_SEE_OFFSET
 
     if move.isQuiet():
         # History heuristic bonus