add pvs(), aka Principal Variation Search

src/eval-simple.c

@@ -0,0 +1,198 @@
+/* eval-simple.c - simple position evaluation.
+ *
+ * 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 <bits.h>
+#include <debug.h>
+
+#include "piece.h"
+#include "eval-simple.h"
+#include "position.h"
+
+/*
+ * Tables are from https://www.chessprogramming.org/Simplified_Evaluation_Function
+ *
+ * Attention! Tables are black point of view (to be visually easier to read).
+ */
+
+static int mg_pawn[] = {
+    0,   0,   0,   0,   0,   0,  0,  0,
+    50, 50,  50,  50,  50,  50, 50, 50,
+    10, 10,  20,  30,  30,  20, 10, 10,
+    5,   5,  10,  25,  25,  10,  5,  5,
+    0,   0,   0,  20,  20,   0,  0,  0,
+    5,  -5, -10,   0,   0, -10, -5,  5,
+    5,  10,  10, -20, -20,  10, 10,  5,
+    0,   0,   0,   0,   0,   0,  0,  0
+};
+
+static int mg_knight[] = {
+    -50, -40, -30, -30, -30, -30, -40, -50,
+    -40, -20,   0,   0,   0,   0, -20, -40,
+    -30,   0,  10,  15,  15,  10,   0, -30,
+    -30,   5,  15,  20,  20,  15,   5, -30,
+    -30,   0,  15,  20,  20,  15,   0, -30,
+    -30,   5,  10,  15,  15,  10,   5, -30,
+    -40, -20,   0,   5,   5,   0, -20, -40,
+    -50, -40, -30, -30, -30, -30, -40, -50
+};
+
+static int mg_bishop[] = {
+    -20, -10, -10, -10, -10, -10, -10, -20,
+    -10,   0,   0,   0,   0,   0,   0, -10,
+    -10,   0,   5,  10,  10,   5,   0, -10,
+    -10,   5,   5,  10,  10,   5,   5, -10,
+    -10,   0,  10,  10,  10,  10,   0, -10,
+    -10,  10,  10,  10,  10,  10,  10, -10,
+    -10,   5,   0,   0,   0,   0,   5, -10,
+    -20, -10, -10, -10, -10, -10, -10, -20
+};
+
+static int mg_rook[] = {
+    0,   0,  0,  0,  0,  0,  0,  0,
+    5,  10, 10, 10, 10, 10, 10,  5,
+    -5,  0,  0,  0,  0,  0,  0, -5,
+    -5,  0,  0,  0,  0,  0,  0, -5,
+    -5,  0,  0,  0,  0,  0,  0, -5,
+    -5,  0,  0,  0,  0,  0,  0, -5,
+    -5,  0,  0,  0,  0,  0,  0, -5,
+    0,   0,  0,  5,  5,  0,  0,  0
+};
+
+static int mg_queen[] = {
+    -20, -10, -10, -5, -5, -10, -10, -20,
+    -10,   0,   0,  0,  0,   0,   0, -10,
+    -10,   0,   5,  5,  5,   5,   0, -10,
+    -5,    0,   5,  5,  5,   5,   0,  -5,
+    0,     0,   5,  5,  5,   5,   0,  -5,
+    -10,   5,   5,  5,  5,   5,   0, -10,
+    -10,   0,   5,  0,  0,   0,   0, -10,
+    -20, -10, -10, -5, -5, -10, -10, -20
+};
+
+static int mg_king[] = {
+    -30, -40, -40, -50, -50, -40, -40, -30,
+    -30, -40, -40, -50, -50, -40, -40, -30,
+    -30, -40, -40, -50, -50, -40, -40, -30,
+    -30, -40, -40, -50, -50, -40, -40, -30,
+    -20, -30, -30, -40, -40, -30, -30, -20,
+    -10, -20, -20, -20, -20, -20, -20, -10,
+    20,  20,   0,   0,   0,   0,  20,  20,
+    20,  30,  10,   0,   0,  10,  30,  20
+};
+
+static int eg_king[] = {
+    -50, -40, -30, -20, -20, -30, -40, -50,
+    -30, -20, -10,   0,   0, -10, -20, -30,
+    -30, -10,  20,  30,  30,  20, -10, -30,
+    -30, -10,  30,  40,  40,  30, -10, -30,
+    -30, -10,  30,  40,  40,  30, -10, -30,
+    -30, -10,  20,  30,  30,  20, -10, -30,
+    -30, -30,   0,   0,   0,   0, -30, -30,
+    -50, -30, -30, -30, -30, -30, -30, -50
+};
+
+/* as pieces bitboard tables start at position 2; we make these tables
+ * bigger.
+ */
+static int *mg_tables[] = {
+    NULL,
+    NULL,
+    mg_pawn,
+    mg_knight,
+    mg_bishop,
+    mg_rook,
+    mg_queen,
+    mg_king
+};
+
+static int *eg_tables[] = {
+    NULL,
+    NULL,
+    mg_pawn,
+    mg_knight,
+    mg_bishop,
+    mg_rook,
+    mg_queen,
+    eg_king
+};
+
+/* to flip vertically a square, we need to XOR it with 56
+ */
+static int mg_table[2][6 + 2][64];
+static int eg_table[2][6 + 2][64];
+
+void eval_simple_init(void)
+{
+#   ifdef DEBUG_EVAL
+    log_f(1, "initializing piece tables\n");
+#   endif
+    for (int piece = BB_PAWN; piece <= BB_KING; ++piece) {
+        for (int square = 0; square < 64; ++square) {
+            mg_table[WHITE][piece][square] = mg_tables[piece][FLIP_V(square)];
+            eg_table[WHITE][piece][square] = eg_tables[piece][FLIP_V(square)];
+            mg_table[BLACK][piece][square] = mg_tables[piece][square];
+            eg_table[BLACK][piece][square] = eg_tables[piece][square];
+        }
+    }
+}
+
+/**
+ * eval_simple() - simple and fast position evaluation
+ * @pos: &position to evaluate
+ *
+ * This function is normally used only during initialization,
+ * or when changing phase (middlegame <--> endgame), as the eval
+ * will be done increntally when doing moves.
+ *
+ * @return: the @pos evaluation in centipawns
+ */
+eval_t eval_simple(pos_t *pos)
+{
+    eval_t eval[2] = { 0, 0 };
+    int eg = simple_is_endgame(pos);
+    int (*gg)[6 + 2][64]= eg? eg_table: mg_table;
+
+    pos->eval_simple_phase = ENDGAME;
+#   ifdef DEBUG_EVAL
+    log_f(1, "phase = %s.\n", eg? "endgame": "midgame");
+#   endif
+
+    for (int color = WHITE; color <= BLACK; ++color) {
+        for (uint piece = PAWN; piece <= KING; piece <<= 1) {
+            int bb = PIECETOBB(piece), cur;
+            u64 _t;
+
+#           ifdef DEBUG_EVAL
+            log_f(1, "p=%u bb=%d %s %s: count=%d val=%ld ", piece, bb, color? "black": "white",
+                  P_SYM(piece), popcount64(pos->bb[color][bb]),
+                  popcount64(pos->bb[color][bb]) * P_VALUE(piece));
+#           endif
+
+            eval[color] += popcount64(pos->bb[color][bb]) * P_LETTER(piece);
+            bit_for_each64_2(cur, _t, pos->bb[color][piece]) {
+#               ifdef DEBUG_EVAL
+                log(1, "sq=%d:%d ", cur, gg[color][bb][cur]);
+#               endif
+                eval[color] += gg[color][bb][cur];
+            }
+#           ifdef DEBUG_EVAL
+            log(1, "\n");
+#           endif
+        }
+    }
+#   ifdef DEBUG_EVAL
+    log_f(1, "white: %d black:%d\n", eval[WHITE], eval[BLACK]);
+#   endif
+
+    return eval[WHITE] - eval[BLACK];
+}

src/eval-simple.h

@@ -0,0 +1,47 @@
+/* eval-simple.h - simple position evaluation.
+ *
+ * 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 EVAL_SIMPLE_H
+#define EVAL_SIMPLE_H
+
+
+#include "chessdefs.h"
+
+/* no queen on board */
+#define simple_no_queen(p, c)              \
+    ( !(p)->bb[c][BB_QUEEN] )
+
+#define simple_one_queen(p, c)             \
+    ( popcount64((p)->bb[c][BB_QUEEN]) == 1 )
+
+#define simple_no_rook(p, c)               \
+    (!(p)->bb[c][BB_ROOK])
+
+#define simple_one_minor_piece(p, c)       \
+    (popcount64((p)->bb[c][BB_KNIGHT] | (p)->bb[c][BB_BISHOP]) == 1)
+
+#define simple_is_endgame(p)                  \
+    ( (simple_no_queen(p, WHITE)   ||         \
+       (simple_one_queen(p, WHITE) &&         \
+        simple_no_rook(p, WHITE)   &&         \
+        simple_one_minor_piece(p, WHITE)))    \
+      &&                                      \
+      (simple_no_queen(p, BLACK)   ||         \
+       (simple_one_queen(p, BLACK) &&         \
+        simple_no_rook(p, BLACK)   &&         \
+        simple_one_minor_piece(p, BLACK))) )
+
+void eval_simple_init(void);
+eval_t eval_simple(pos_t *pos);
+
+#endif  /* EVAL_SIMPLE_H */

src/eval.c

@@ -1,6 +1,6 @@
 /* eval.c - static position evaluation.
  *
- * Copyright (C) 2021 Bruno Raoult ("br")
+ * Copyright (C) 2021-2023 Bruno Raoult ("br")
  * Licensed under the GNU General Public License v3.0 or later.
  * Some rights reserved. See COPYING.
  *
@@ -16,6 +16,7 @@
 #include <list.h>
 #include <debug.h>
 
+#include "position.h"
 #include "eval.h"
 
 inline eval_t eval_material(pos_t *pos, bool color)
@@ -52,6 +53,9 @@ eval_t eval(pos_t *pos)
 {
     eval_t material[2] = {0}, control[2] = {0};
 
+    if (pos->eval != EVAL_INVALID)
+        return pos->eval;
+
     /* 1) pieces value */
     material[WHITE] = eval_material(pos, WHITE);
     material[BLACK] = eval_material(pos, BLACK);
@@ -85,7 +89,7 @@ eval_t eval(pos_t *pos)
 #   ifdef DEBUG_EVAL
     log_f(2, "eval: %d\n", res);
 #   endif
-
+    pos->eval = res;
     return res;
 }
 

src/eval.h

@@ -14,7 +14,20 @@
 #ifndef EVAL_H
 #define EVAL_H
 
-#include "position.h"
+#include <limits.h>
+
+#include "chessdefs.h"
+#include "piece.h"
+
+#define EVAL_MAX       \
+    KING_VALUE     +   \
+    QUEEN_VALUE  * 9 + \
+    ROOK_VALUE   * 2 + \
+    BISHOP_VALUE * 2 + \
+    KNIGHT_VALUE * 2
+
+#define EVAL_MIN     (-EVAL_MAX)
+#define EVAL_INVALID INT_MIN
 
 eval_t eval_material(pos_t *pos, bool color);
 eval_t eval_mobility(pos_t *pos, bool color);

src/search.c

@@ -21,8 +21,15 @@
 #include "search.h"
 
 /**
- * negamax() - the negamax tree.
+ * negamax() - search position negamax.
+ * @pos: &position to search
+ * @depth: Wanted depth.
+ * @color: 1 for white, -1 for black.
  *
+ * Calculate the negamax value of @pos. This is an extensive search, with
+ * absolutely no cutoff.
+ *
+ * @return: The @pos negamax evaluation.
  */
 eval_t negamax(pos_t *pos, int depth, int color)
 {
@@ -30,40 +37,180 @@ eval_t negamax(pos_t *pos, int depth, int color)
     pos_t *newpos;
     eval_t best = EVAL_MIN, score;
 
-    //printf("depth=%d\n", depth);
-    moves_gen_all(pos);
-    //pos_check(pos);
     if (depth == 0) {
-        score = eval(pos);
+        moves_gen_all_nomoves(pos);
-        //printf("evalnega=%d turn=%d color=%d", score, pos->turn, color);
+        score = eval(pos) * color;
-        score *= color;
-        //printf(" --> evalnega=%d\n", score);
         return score;
     }
-    //moves_print(pos, 0);
+    moves_gen_all(pos);
     list_for_each_entry(move, &pos->moves[pos->turn], list) {
         log(1, "%.*s", 5 - depth, "                ");
         newpos = move_do(pos, move);
-        //move_print(0, move, 0);
-        //printf("color piece = %d\n", COLOR(move->piece));
-        //printf("turns=%d/%d\n", pos->turn, newpos->turn);
-        //fflush(stdout);
         score = -negamax(newpos, depth - 1, -color);
+        pos->node_count += newpos->node_count;
         move->negamax = score;
-        //printf("move=");
-        //move_print(0, move, 0);
-        //printf("score=%d\n", score);
-
         if (score > best) {
             best = score;
             pos->bestmove = move;
-#           ifdef DEBUG_SEARCH
-            //printf("depth=%d best move=", depth);
-            //move_print(0, &bestmove, 0);
-            //printf(" eval=%d\n", best);
-#           endif
         }
         move_undo(newpos, move);
     }
     return best;
 }
+
+
+/**
+ * pvs() - Principal Variation Search.
+ * @pos: &position to search
+ * @depth: wanted depth.
+ * @alpha: alpha value.
+ * @beta: beta value.
+ * @color: 1 for white, -1 for black.
+ *
+ * Calculate the PVS value of @pos.
+ * See https://en.wikipedia.org/wiki/Principal_variation_search
+ *
+ * @return: The @pos PVS evaluation.
+ */
+eval_t pvs(pos_t *pos, int depth, int alpha, int beta, int color)
+{
+    move_t *move;
+    pos_t *newpos;
+    eval_t score;
+    int n = 0;
+
+    if (depth == 0) {
+        //return quiesce(p, alpha, beta);           /* leaf node */
+        moves_gen_all_nomoves(pos);
+        score = eval(pos) * color;
+        return score;
+    }
+
+    moves_gen_eval_sort(pos);
+
+    //moves_print(pos, M_PR_EVAL);
+    list_for_each_entry(move, &pos->moves[pos->turn], list) {
+        log(1, "%.*s", 5 - depth, "                ");
+        newpos = move->pos;
+        log_f(1, "depth=%d eval=%d move=", depth, move->eval);
+        move_print(0, move, M_PR_EVAL);
+        log(1, "\n");
+        if (!n++) {                               /* first child */
+            score = -pvs(newpos, depth - 1, -beta, -alpha, -color);
+        } else {
+            /* search with a null window */
+            score = -pvs(newpos, depth - 1, -alpha - 1, -alpha, -color);
+            if (score > alpha && score < beta) {
+                /* if failed high, do a full re-search */
+                score = -pvs(newpos, depth - 1, -beta, -score, -color);
+            }
+        }
+        if (score > alpha) {
+            alpha = score;
+            pos->bestmove = move;
+        }
+        move_undo(newpos, move);
+        move->pos = NULL;
+        pos->node_count += newpos->node_count;
+        move->negamax = score;
+        // alpha = max(alpha, score);
+        if (alpha > beta) {                       /* beta cut-off */
+            break;
+        }
+    }
+
+    return alpha;
+}
+
+/*
+ * int negascout (pos_t *pos, int depth, int alpha, int beta )
+ * {                     /\* compute minimax value of position p *\/
+ *     move_t *move;
+ *     pos_t *newpos;
+ *     eval_t best = EVAL_MIN, score;
+ *
+ *     int a, b, t, i;
+ *
+ *     if (depth == 0) {
+ *         //return quiesce(p, alpha, beta);           /\* leaf node *\/
+ *         moves_gen_all_nomoves(pos);
+ *         score = eval(pos) * color;
+ *         return score;
+ *     }
+ *     moves_gen_all(pos);
+ *     a = alpha;
+ *     b = beta;
+ *     list_for_each_entry(move, &pos->moves[pos->turn], list) {
+ *         log(1, "%.*s", 5 - depth, "                ");
+ *         newpos = move_do(pos, move);
+ * //    for ( i = 1; i <= w; i++ ) {
+ *         t = -negascout (newpos, depth - 1, -b, -alpha);
+ *         if ( (t > a) && (t < beta) && (i > 1) )
+ *             t = -NegaScout ( p_i, -beta, -alpha ); /\* re-search *\/
+ *         alpha = max( alpha, t );
+ *         if ( alpha >= beta )
+ *             return alpha;                            /\* cut-off *\/
+ *         b = alpha + 1;                  /\* set new null window *\/
+ *     }
+ *     return alpha;
+ * }
+ */
+
+/*
+ * int quiesce(pos_t *pos, int alpha, int beta)
+ * {
+ *     int stand_pat = eval(pos);
+ *
+ *     if( stand_pat >= beta )
+ *         return beta;
+ *     if( alpha < stand_pat )
+ *         alpha = stand_pat;
+ *
+ *     /\*
+ *      * until( every_capture_has_been_examined )  {
+ *      *     MakeCapture();
+ *      *     score = -Quiesce( -beta, -alpha );
+ *      *     TakeBackMove();
+ *      *
+ *      *     if( score >= beta )
+ *      *         return beta;
+ *      *     if( score > alpha )
+ *      *        alpha = score;
+ *      * }
+ *      *\/
+ *     return alpha;
+ * }
+ */
+
+/**
+ * ab_negamax() - search position negamax with alpha-beta cutoff.
+ * @pos: &position to search
+ * @depth: Wanted depth.
+ * @color: 1 for white, -1 for black.
+ *
+ * Calculate the negamax value of @pos, with alpha-beta pruning.
+ *
+ * @return: The @pos negamax evaluation.
+ */
+/*int ab_negamax(pos_t *pos, int alpha, int beta, int depth)
+{
+    move_t *move;
+    pos_t *newpos;
+    eval_t best = EVAL_MIN, score;
+
+    if(depth == 0) {
+       //return quiesce( alpha, beta );
+        moves_gen_all_nomoves(pos);
+       score = eval(pos) * color;
+       return score;
+    }
+   for ( all moves)  {
+      score = -alphaBeta( -beta, -alpha, depthleft - 1 );
+      if( score >= beta )
+         return beta;   //  fail hard beta-cutoff
+      if( score > alpha )
+         alpha = score; // alpha acts like max in MiniMax
+   }
+   return alpha;
+}
+*/

src/search.h

@@ -14,12 +14,9 @@
 #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, int color);
+eval_t pvs(pos_t *pos, int depth, int alpha, int beta, int color);
 
 #endif  /* SEARCH_H */