Add pos negamax function

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;
+}