From fd808ef5e046af12177d210338ff081e3ca899b1 Mon Sep 17 00:00:00 2001
From: Quinten Kock <quintenkock@gmail.com>
Date: Thu, 18 Jun 2020 21:19:20 +0200
Subject: [PATCH] Implement unmaking and castle rights

---
 Board.h | 46 ++++++++++++++++++++++++++++++----------------
 1 file changed, 30 insertions(+), 16 deletions(-)

diff --git a/Board.h b/Board.h
index a685923..ed0f4bc 100644
--- a/Board.h
+++ b/Board.h
@@ -52,7 +52,7 @@ void board_init() {
 
 
 struct Unmove {
-	byte sq_from;	// 0b(1unused)(3rank)(1unused)(3file)
+	byte sq_from;	// 0b(1kingside_castle?)(3rank)(1queenside_castle?)(3file)
 	byte sq_to;	// 0b(1promoted?)(3rank)(1ep_capture?)(3file)
 	byte captured;	// 0b(4enpassantinfo)(1color)(3piecetype)
 	byte revmov;	// 8bit integer
@@ -136,9 +136,9 @@ void make(Move m) {
 	byte piece_type = field[m.sq_from] & 0x7;
 
 	if(u.captured || piece_type == W_PAWN) {
-		field[PTR_REVMOV]++;
-	} else {
 		field[PTR_REVMOV] = 0;
+	} else {
+		field[PTR_REVMOV]++;
 	}
 
 	// Calculate the move 'amount' (unique signature for dx,dy)
@@ -162,23 +162,28 @@ void make(Move m) {
 	}
 
 	// Handle castling rights
+	// First store the current rights in the unmove
+	byte our_rights = field[PTR_SIDE_AND_CASTLERIGHT] >> (1 + 2*black_moving());
+	if(our_rights & 0b10) // kingside allowed
+		u.sq_from |= 0x80;
+	if(our_rights & 0b01) // queenside allowed
+		u.sq_from |= 0x08;
 	// We are doing the simple way:
 	// unset it any time a move is made from the original position.
 	// TODO handle castle rights and unmake
 	if(m.sq_from == 0x00) // white queenside rook
 		field[PTR_SIDE_AND_CASTLERIGHT] &= ~0b00010;
-	if(m.sq_from == 0x07) // white kingside rook
+	else if(m.sq_from == 0x07) // white kingside rook
 		field[PTR_SIDE_AND_CASTLERIGHT] &= ~0b00100;
-	if(m.sq_from == 0x04) // white king
+	else if(m.sq_from == 0x04) // white king
 		field[PTR_SIDE_AND_CASTLERIGHT] &= ~0b00110;
-	if(m.sq_from == 0x70) // black queenside rook
+	else if(m.sq_from == 0x70) // black queenside rook
 		field[PTR_SIDE_AND_CASTLERIGHT] &= ~0b01000;
-	if(m.sq_from == 0x77) // black kingside rook
+	else if(m.sq_from == 0x77) // black kingside rook
 		field[PTR_SIDE_AND_CASTLERIGHT] &= ~0b10000;
-	if(m.sq_from == 0x74) // black king
+	else if(m.sq_from == 0x74) // black king
 		field[PTR_SIDE_AND_CASTLERIGHT] &= ~0b11000;
 
-
 	// TODO: test enpassant code more than basics
 
 	// handle enpassant capture
@@ -233,35 +238,44 @@ void unmake() {
 	Unmove u = read_unmove();
 	field[PTR_REVMOV] = u.revmov;
 
+	byte sq_from = u.sq_from & 0x77;
 	byte sq_to = u.sq_to & 0x77;
 	byte prom_ep_capt = u.sq_to & 0x88;
 
 
 	if(prom_ep_capt == 0) {
 		// regular move
-		field[u.sq_from] = field[sq_to];
+		field[sq_from] = field[sq_to];
 	} else if (prom_ep_capt == 0x80) {
 		// piece was promoted
 		// so the source is a pawn
-		field[u.sq_from] = W_PAWN | (field[u.sq_to] & 0b1000);
+		field[sq_from] = W_PAWN | (field[sq_to] & 0b1000);
 	} else if (prom_ep_capt == 0x08) {
 		// we did an enpassant capture
-		byte ep_sq = (u.sq_to & 0x07) | (u.sq_from & 0x70);
+		byte ep_sq = (sq_to & 0x07) | (sq_from & 0x70);
 		field[ep_sq] = W_PAWN | black_moving() << 3;
 		// also undo the regular move
-		field[u.sq_from] = field[sq_to];
+		field[sq_from] = field[sq_to];
+	}
+
+	byte castleright_offset = 3 - 2*black_moving();
+	if(u.sq_from & 0x80) {
+		// restore king side castling rights
+		field[PTR_SIDE_AND_CASTLERIGHT] |= 0b10 << castleright_offset;
+	}
+	if(u.sq_from & 0x08) {
+		field[PTR_SIDE_AND_CASTLERIGHT] |= 0b01 << castleright_offset;
 	}
-	// TODO handle castling rights
 
 	int sq_diff = (int)sq_to - (int)u.sq_from;
 	int sq_diff_abs = abs(sq_diff);
-	if((field[u.sq_from] & 0x7) == W_KING && sq_diff_abs == 2) {
+	if((field[sq_from] & 0x7) == W_KING && sq_diff_abs == 2) {
 		// we castled
 		byte castle_source = 0x70*!black_moving();
 		if(sq_diff == 2) {
 			castle_source += 0x7;
 		}
-		byte castle_target = u.sq_from + (sq_diff/2);
+		byte castle_target = sq_from + (sq_diff/2);
 		// move rook back to original position
 		field[castle_source] = field[castle_target];
 		// and clear where it was put