Add pos negamax function

Makefile

@@ -61,6 +61,7 @@ CPPFLAGS  += -DDEBUG_FEN                     # FEN decoding
 CPPFLAGS  += -DDEBUG_MOVE                    # move generation
 CPPFLAGS  += -DDEBUG_EVAL                    # eval functions
 CPPFLAGS  += -DDEBUG_PIECE                   # piece list management
+CPPFLAGS  += -DDEBUG_SEARCH                  # move search
 
 ##################################### General targets
 .PHONY: compile cflags all clean cleanall

src/move.c

@@ -62,6 +62,20 @@ void moves_pool_stats()
         pool_stats(moves_pool);
 }
 
+/**
+ * move_print() - print a move
+ * @movenum: move number
+ * @move: &move to display
+ * @flags: options to display
+ *
+ * Possible flags are:
+ * M_PR_CAPT:  print move if capture
+ * M_PR_NCAPT: print move if non capture
+ * M_PR_NUM:   print also move number
+ * M_PR_LONG:  print long notation
+ *
+ * @return: 0 if nothing printed, 1 otherwise
+ */
 int move_print(int movenum, move_t *move, move_flags_t flags)
 {
     if (flags & M_PR_CAPT && !(move->flags & M_CAPTURE)) {
@@ -88,10 +102,10 @@ int move_print(int movenum, move_t *move, move_flags_t flags)
         printf("%s%c%c", P_SYM(move->piece),
                FILE2C(F88(move->from)),
                RANK2C(R88(move->from)));
-        if (move->taken) {
+        if (move->flags & M_CAPTURE) {
             printf("x");
             if (flags & M_PR_LONG)
-                printf("%s", P_SYM(move->taken));
+                printf("%s", P_SYM(move->capture));
         } else {
             printf("-");
         }
@@ -172,9 +186,9 @@ static move_t *move_add(pos_t *pos, piece_t piece, square_t from,
     move->piece = piece;
     move->from = from;
     move->to = to;
-    move->taken = board[to].piece;
+    move->capture = board[to].piece;
     move->flags = M_NORMAL;
-    if (move->taken)
+    if (move->capture)
         move->flags |= M_CAPTURE;
 #   ifdef DEBUG_MOVE
     log_i(3, "added move from %c%c to %c%c\n",
@@ -336,10 +350,10 @@ int pseudo_moves_pawn(pos_t *pos, piece_list_t *ppiece, bool doit)
 #       endif
         if (sq_file == ep_file - 1 || sq_file == ep_file + 1) {
             square_t t_square = SQ88(ep_file, rank5); /* taken pawn square */
-            piece_t taken = board[t_square].piece;
+            piece_t captured = board[t_square].piece;
             move = move_pawn_add(pos, piece | color , square, pos->en_passant, rank7);
             move->flags |= M_EN_PASSANT | M_CAPTURE;
-            move->taken = taken;
+            move->capture = captured;
             pos->mobility[color]++;
             count++;
         }
@@ -668,11 +682,7 @@ pos_t *move_do(pos_t *pos, move_t *move)
     int color = COLOR(piece);
     square_t from = move->from, to = move->to;
 
-    /* todo: en passant, castle
-     */
-    SET_COLOR(new->turn, OPPONENT(color));        /* pos color */
-
-    if (move->taken || PIECE(piece) == PAWN)      /* 50 moves */
+    if (move->capture || PIECE(piece) == PAWN)    /* 50 moves */
         new->clock_50 = 0;
     else
         new->clock_50++;
@@ -739,12 +749,14 @@ pos_t *move_do(pos_t *pos, move_t *move)
     new->board[from].piece = 0;
     new->board[from].s_piece = NULL;
 
+    SET_COLOR(new->turn, OPPONENT(color));        /* pos color */
+
     return new;
 }
 
 void move_undo(pos_t *pos, __unused move_t *move)
 {
-    pos_clear(pos);
+    pos_del(pos);
 }
 
 #ifdef BIN_move

src/move.h

@@ -41,7 +41,7 @@ typedef unsigned char move_flags_t;
 typedef struct move_s {
     piece_t piece;
     square_t from, to;
-    piece_t taken;                                /* captured piece */
+    piece_t capture;                              /* captured piece */
     piece_t promotion;                            /* promoted piece */
     move_flags_t flags;
     struct list_head list;                        /* next move */

src/search.c

@@ -0,0 +1,51 @@
+/* search.c - search good moves.
+ *
+ * Copyright (C) 2023 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+
+
+#include <br.h>
+#include <list.h>
+#include <debug.h>
+
+#include "move.h"
+#include "eval.h"
+#include "search.h"
+
+/**
+ * negamax() - the negamax tree.
+ *
+ */
+eval_t negamax(pos_t *pos, int depth)
+{
+    move_t *move, *bestmove;
+    pos_t *newpos;
+    eval_t best = EVAL_MIN, score;
+
+    moves_gen_all(pos);
+    if (depth == 0)
+        return eval(pos) * pos->turn == WHITE? 1: -1;
+
+    list_for_each_entry(move, &pos->moves[pos->turn], list) {
+        newpos = move_do(pos, move);
+        score = -negamax(newpos, depth - 1 );
+        if(score > best) {
+            best = score;
+            bestmove = move;
+#           ifdef DEBUG_SEARCH
+            log_f(2, "depth=%d best move=", best);
+            move_print(0, bestmove, M_PR_LONG);
+            log_f(2, " eval=%d\n", best);
+#           endif
+        }
+    }
+    return best;
+}

src/search.h

@@ -0,0 +1,25 @@
+/* search.h - search for perfect move.
+ *
+ * Copyright (C) 2021 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+
+#ifndef SEARCH_H
+#define SEARCH_H
+
+#include <limits.h>
+#include "position.h"
+
+#define EVAL_MIN INT_MIN
+#define EVAL_MAX INT_MAX
+
+eval_t negamax(pos_t *pos, int depth);
+
+#endif  /* SEARCH_H */