move-do: use castling flags, other improvements (~12% on perft)

- always set K square and castling flags (remove expensive tests on K and castling flags)
- simplify castling rook move

src/move-do.c

@@ -25,6 +25,20 @@
 #include "move-do.h"
 #include "hash.h"
 
+/**
+ * sq_castle - castling rights per square.
+ *
+ * position castling rights mask has to be AND'ed with this array 'from' and 'to'.
+ */
+castle_rights_t sq_castle[64] = {
+    [A1] = ~CASTLE_WQ, [B1 ... D1] = ~CASTLE_NONE,
+    [E1] = ~CASTLE_W,  [F1 ... G1] = ~CASTLE_NONE,
+    [H1] = ~CASTLE_WK, [A2 ... H7] = ~CASTLE_NONE,
+    [A8] = ~CASTLE_BQ, [B8 ... D8] = ~CASTLE_NONE,
+    [E8] = ~CASTLE_B,  [F8 ... G8] = ~CASTLE_NONE,
+    [H8] = ~CASTLE_BK,
+};
+
 /**
  * move_do() - do move.
  * @pos:    &pos_t position
@@ -60,9 +74,8 @@ pos_t *move_do(pos_t *pos, const move_t move, state_t *state)
 
     *state = pos->state;                          /* save irreversible changes */
 
-    /* update key: switch turn, reset castling and ep */
+    /* update key: switch turn, reset ep */
     key ^= zobrist_turn;
-    key ^= zobrist_castling[pos->castle];
     key ^= zobrist_ep[EP_ZOBRIST_IDX(pos->en_passant)];
 
     ++pos->clock_50;
@@ -74,80 +87,69 @@ pos_t *move_do(pos_t *pos, const move_t move, state_t *state)
 
     bug_on(COLOR(piece) != us);
 
-    if (is_promotion(move)) {
+    /* special moves: captures, pawn double push, en-passant, castling.
-        bug_on(sq_rank(to) != sq_rel_rank(RANK_8, us));
+     * All these moves are exclusive (so we use if ... else)
-        new_piece = MAKE_PIECE(move_promoted(move), us);
+     */
-    }
+    if (captured != EMPTY) {                      /* capture: remove piece */
-
-    if (captured != EMPTY) {
         pos->clock_50 = 0;
         bug_on(pos->board[to] == EMPTY || COLOR(pos->captured) != them);
         key ^= zobrist_pieces[captured][to];
-        pos_clr_sq(pos, to);                      /* clear square */
+        pos_clr_sq(pos, to);
-    } else if (is_castle(move)) {                 /* handle rook move */
+    } else if (ptype == PAWN) {
-        square_t rookfrom, rookto;
-        if (to > from) {
-            rookfrom = sq_rel(H1, us);
-            rookto = sq_rel(F1, us);
-        } else {
-            rookfrom = sq_rel(A1, us);
-            rookto = sq_rel(D1, us);
-        }
-        key ^= zobrist_pieces[pos->board[rookfrom]][rookto] ^
-            zobrist_pieces[pos->board[rookfrom]][rookfrom];
-        pos_set_sq(pos, rookto, pos->board[rookfrom]);
-        pos_clr_sq(pos, rookfrom);
-        pos->castle = clr_castle(pos->castle, us);
-    } else if (ptype == PAWN) {                   /* pawn non capture or e.p. */
         pos->clock_50 = 0;
-        if (from + up + up == to) {               /* if pawn double push, set e.p. */
+        if (from + up + up == to) {               /* double push: set e.p. */
             square_t ep = from + up;
+            /* check that opponent can e.p. */
             if (bb_pawn_attacks[us][ep] & pos->bb[them][PAWN]) {
                 pos->en_passant = ep;
                 key ^= zobrist_ep[EP_ZOBRIST_IDX(pos->en_passant)];
             }
-        } else if (is_enpassant(move)) {          /* clear grabbed pawn */
+        } else if (is_enpassant(move)) {          /* e.p.: clear grabbed pawn */
             square_t grabbed = to - up;
             piece_t pc = pos->board[grabbed];
             key ^= zobrist_pieces[pc][grabbed];
             pos_clr_sq(pos, grabbed);
         }
+    } else if (is_castle(move)) {                 /* castling: handle rook move */
+        square_t rookfrom, rookto;
+        if (to > from) {                          /* o-o */
+            rookfrom = to + 1;
+            rookto = to - 1;
+        } else {                                  /* o-o-o */
+            rookfrom = to - 2;
+            rookto = to + 1;
+        }
+        key ^= zobrist_pieces[pos->board[rookfrom]][rookto] ^
+            zobrist_pieces[pos->board[rookfrom]][rookfrom];
+        pos_set_sq(pos, rookto, pos->board[rookfrom]);
+        pos_clr_sq(pos, rookfrom);
+    }
+
+    /* common part: captures and non captures
+     * We could improve slightly, as en-passant and double push will make
+     * the following tests.
+     * Improvement could be to add promotion test and king test twice above.
+     * (in capture and after ).
+     */
+    if (is_promotion(move)) {
+        bug_on(sq_rank(to) != sq_rel_rank(RANK_8, us));
+        new_piece = MAKE_PIECE(move_promoted(move), us);
     }
 
     key ^= zobrist_pieces[piece][from] ^ zobrist_pieces[new_piece][to];
-    pos_clr_sq(pos, from);                        /* clear "from" and set "to" */
+    pos_clr_sq(pos, from);
     pos_set_sq(pos, to, new_piece);
 
-    if (ptype == KING)
+    /* update castling flags */
-        pos->king[us] = to;
-
-    /* update castling flags
-     * As we always consider flags are valid, we :
-     * - adjust our flags if relative from is "E1", "A1", H1"
-     * - adjust opp flags if relative to   if "A8", H8"
-     */
-    if (can_castle(pos->castle, us)) {            /* do we save time with this test ? */
-        square_t rel_e1 = sq_rel(E1, us);
-        square_t rel_a1 = sq_rel(A1, us);
-        square_t rel_h1 = sq_rel(H1, us);
-        if (from == rel_e1)
-            pos->castle = clr_castle(pos->castle, us);
-        else if (from == rel_a1)
-            pos->castle = clr_ooo(pos->castle, us);
-        else if (from == rel_h1)
-            pos->castle = clr_oo(pos->castle, us);
-    }
-    if (can_castle(pos->castle, them)) {
-        square_t rel_a8 = sq_rel(A8, us);
-        square_t rel_h8 = sq_rel(H8, us);
-        if (to == rel_a8)
-            pos->castle = clr_ooo(pos->castle, them);
-        else if (to == rel_h8)
-            pos->castle = clr_oo(pos->castle, them);
-    }
-
-    /* update castling rights key */
     key ^= zobrist_castling[pos->castle];
+    pos->castle &= sq_castle[from] & sq_castle[to];
+    key ^= zobrist_castling[pos->castle];
+
+    //if (ptype == KING) {
+    //    pos->king[us] = to;
+    //} else
+    /* do this always, cheaper than test on K move */
+    pos->king[us] = ctz64(pos->bb[us][KING]);
 
     pos->key = key;
 
@@ -180,33 +182,43 @@ pos_t *move_undo(pos_t *pos, const move_t move, const state_t *state)
     piece_t piece = pos->board[to];
     int up = sq_up(them);
 
+    /* common part: captures and non captures
+     * We could improve slightly, as en-passant and double push will make
+     * the following tests.
+     * Improvement could be to add promotion test and king test twice above.
+     * (in capture and after ).
+     */
     if (is_promotion(move))
         piece = MAKE_PIECE(PAWN, us);
 
-    pos_clr_sq(pos, to);                          /* always clear "to" ... */
+    pos_clr_sq(pos, to);
-    pos_set_sq(pos, from, piece);                 /* ... and set "from" */
+    pos_set_sq(pos, from, piece);
 
-    if (PIECE(piece) == KING)
+    /* special moves: capture, king (+ castling), en-passant
-        pos->king[us] = from;
+     */
-
+    if (pos->captured != EMPTY) {                 /* captured: restore piece */
-    if (pos->captured != EMPTY) {
+        pos_set_sq(pos, to, pos->captured);
-        pos_set_sq(pos, to, pos->captured);       /* restore captured piece */
+    } else if (is_castle(move)) {                 /* castle: rook move */
-    } else if (is_castle(move)) {                 /* make reverse rook move */
         square_t rookfrom, rookto;
-        if (to > from) {
+        if (to > from) {                          /* o-o */
-            rookfrom = sq_rel(F1, us);
+            rookfrom = to - 1;
-            rookto = sq_rel(H1, us);
+            rookto = to + 1;
-        } else {
+        } else {                                  /* o-o-o */
-            rookfrom = sq_rel(D1, us);
+            rookfrom = to + 1;
-            rookto = sq_rel(A1, us);
+            rookto = to - 2;
         }
         pos_set_sq(pos, rookto, pos->board[rookfrom]);
         pos_clr_sq(pos, rookfrom);
-    } else if (is_enpassant(move)) {              /* restore grabbed pawn */
+    } else if (is_enpassant(move)) {              /* e.p.: restore grabbed pawn */
         square_t grabbed = to + up;
         pos_set_sq(pos, grabbed, MAKE_PIECE(PAWN, them));
     }
 
+    /* do this always, cheaper than test on K move */
+    pos->king[us] = ctz64(pos->bb[us][KING]);
+    //if (PIECE(piece) == KING)
+    //    pos->king[us] = from;
+
     pos->state = *state;                          /* restore irreversible changes */
     pos->turn = us;
     return pos;
@@ -284,7 +296,7 @@ pos_t *move_do_alt(pos_t *pos, const move_t move, state_t *state)
     }
 
     key ^= zobrist_pieces[piece][from] ^ zobrist_pieces[new_piece][to];
-    pos_clr_sq(pos, from);                        /* clear "from" and set "to" */
+    pos_clr_sq(pos, from);
     pos_set_sq(pos, to, new_piece);
 
     if (ptype == KING)

src/move-do.h

@@ -14,8 +14,11 @@
 #ifndef MOVE_DO_H
 #define MOVE_DO_H
 
+#include "chessdefs.h"
 #include "position.h"
 
+extern castle_rights_t sq_castle[64];             /* to adjust castling rights */
+
 pos_t *move_do(pos_t *pos, const move_t move, state_t *state);
 pos_t *move_undo(pos_t *pos, const move_t move, const state_t *state);