From 86393cf0e2344f81f59db87ec541c6a7ed55d651 Mon Sep 17 00:00:00 2001
From: Adam <adammegarules1@gmail.com>
Date: Wed, 19 Aug 2026 11:48:06 +0200
Subject: perf(move): making undo move use incremental bitboard aproah instead
 of generation from scrath each time

---
 src/board/board.cpp | 73 ++++++++++++++++++++++++++++-------------------------
 src/board/board.hpp |  1 -
 2 files changed, 38 insertions(+), 36 deletions(-)

diff --git a/src/board/board.cpp b/src/board/board.cpp
index 4ca0667..7525fab 100644
--- a/src/board/board.cpp
+++ b/src/board/board.cpp
@@ -1,4 +1,5 @@
 #include <cassert>
+#include <chrono>
 #include <cstddef>
 #include <cstdint>
 #include <cstdlib>
@@ -114,8 +115,8 @@ bool isRepetionDraw(uint64_t key, Game *g) {
   return repetions >= 3;
 };
 
-static void movePiece(uint8_t fromSquare, Piece fromPiece, uint8_t toSquare,
-                      Piece toPiece, Game *g) {
+static void movePiece(const uint8_t &fromSquare, const Piece &fromPiece,
+                      const uint8_t &toSquare, const Piece &toPiece, Game *g) {
   uint64_t from = 1ULL << fromSquare;
   uint64_t to = 1ULL << toSquare;
 
@@ -238,6 +239,8 @@ Undo MakeMove(uint16_t move, Game *g) {
 
   // promotion is always set and should only be aplied when reached final rank
   // (default: knight)
+  // because we use only two bits of memory for promotion we cant represent a
+  // none type so we always have knight set and only it last rank and its pawn
   if (piece.type == PAWN &&
       IndexToPosition(toSquare).rank == (piece.color ? 7 : 0)) {
     piece.type = promotion;
@@ -373,13 +376,34 @@ Undo MakeMove(uint16_t move, Game *g) {
   return undo;
 };
 void UndoMove(Undo undo, Game *g) {
-  g->pieces[undo.from] = undo.movedPiece;
+  movePiece(undo.to, undo.movedPiece, undo.from, {.type = NONEPIECE}, g);
+
+  // uint64_t from = 1ULL << undo.from;
+  uint64_t to = 1ULL << undo.to;
 
   g->pieces[undo.to] = undo.capturedPiece;
+  if (undo.capturedPiece.type != NONEPIECE) {
+    g->PieceBitboards[undo.capturedPiece.color][undo.capturedPiece.type] ^= to;
+    if (undo.capturedPiece.color) {
+      g->WhitePieceBitboard ^= to;
+    } else {
+      g->BlackPieceBitboard ^= to;
+    }
+  };
 
   if (undo.wasEnPassantCapture) {
+    const uint64_t capturedSquare =
+        1ULL << PositionToIndex(undo.enPassantCapturedSquare);
     g->pieces[PositionToIndex(undo.enPassantCapturedSquare)] =
         undo.enPassantCapturedPiece;
+    g->PieceBitboards[undo.enPassantCapturedPiece.color]
+                     [undo.enPassantCapturedPiece.type] |= capturedSquare;
+    if (undo.enPassantCapturedPiece.color) {
+      g->WhitePieceBitboard |= capturedSquare;
+
+    } else {
+      g->BlackPieceBitboard |= capturedSquare;
+    }
   }
 
   g->turn = undo.oldTurn;
@@ -406,11 +430,11 @@ void UndoMove(Undo undo, Game *g) {
       Position rookTo = IndexToPosition(undo.from);
       rookTo.file = 7;
 
-      g->pieces[PositionToIndex(rookTo)] = g->pieces[PositionToIndex(rookFrom)];
-      g->pieces[PositionToIndex(rookFrom)] = {
-          .color = false,
-          .type = NONEPIECE,
-      };
+      movePiece(static_cast<uint8_t>(PositionToIndex(rookFrom)),
+                g->pieces[PositionToIndex(rookFrom)],
+                static_cast<uint8_t>(PositionToIndex(rookTo)),
+                {.type = NONEPIECE}, g);
+
     } else {
       // d -> a
       Position rookFrom = IndexToPosition(undo.from);
@@ -419,35 +443,14 @@ void UndoMove(Undo undo, Game *g) {
       Position rookTo = IndexToPosition(undo.from);
       rookTo.file = 0;
 
-      g->pieces[PositionToIndex(rookTo)] = g->pieces[PositionToIndex(rookFrom)];
-      g->pieces[PositionToIndex(rookFrom)] = {
-          .color = false,
-          .type = NONEPIECE,
-      };
-    }
+      movePiece(static_cast<uint8_t>(PositionToIndex(rookFrom)),
+                g->pieces[PositionToIndex(rookFrom)],
+                static_cast<uint8_t>(PositionToIndex(rookTo)),
+                {.type = NONEPIECE}, g);
+    };
   }
 
   g->history.pop_back();
 
-  UpdateHelpers(g);
-};
-void UpdateHelpers(Game *g) {
-  g->PieceBitboard = 0;
-  g->WhitePieceBitboard = 0;
-  g->BlackPieceBitboard = 0;
-  std::memset(g->PieceBitboards, 0, sizeof(g->PieceBitboards));
-  for (uint8_t i = 0; i < 64; i++) {
-    Piece piece = g->pieces[i];
-    if (piece.type == NONEPIECE) {
-      continue;
-    }
-    g->PieceBitboards[piece.color][piece.type] |= (1ULL << i);
-
-    if (piece.color) {
-      g->WhitePieceBitboard |= (1ULL << i);
-    } else {
-      g->BlackPieceBitboard |= (1ULL << i);
-    }
-  }
   g->PieceBitboard = g->WhitePieceBitboard | g->BlackPieceBitboard;
-}
+};
\ No newline at end of file
diff --git a/src/board/board.hpp b/src/board/board.hpp
index a2c4e1f..a64289e 100644
--- a/src/board/board.hpp
+++ b/src/board/board.hpp
@@ -109,5 +109,4 @@ Undo MakeMove(uint16_t move, Game *g);
 void UndoMove(Undo undo, Game *g);
 
 Position FindKing(const Game &g, bool color);
-void UpdateHelpers(Game *g);
 #endif /* SRC_BOARD_H_ */
-- 
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