From 0ff41c408b77f0edc3ada4e16f743a8f6b707a7e Mon Sep 17 00:00:00 2001
From: Bruno Raoult <braoult@gmail.com>
Date: Sun, 4 Aug 2024 09:37:58 +0200
Subject: [PATCH] add repetition detection, root position count

- hist.c: add hist_next() - get next entry in history
- state_t: remove plycount, clock_50 -> ply50, add phase, repcount
- pos_t: add plycount, plyroot
- state_t moved to chessdefs.h
- perft-test: split perft from do_perft (todo for perft_alt)
- position.c: add pos_repcount()
- search.c: add is_draw()
- uci: set root position (after moves), adjust history moves repcount
---
 Makefile          |  2 +-
 src/brchess.c     |  4 +--
 src/chessdefs.h   |  2 +-
 src/eval-defs.h   |  2 --
 src/eval.c        |  2 +-
 src/eval.h        |  2 +-
 src/fen.c         |  6 ++--
 src/hist.c        | 20 +++++++++---
 src/hist.h        |  1 +
 src/move-do.c     | 24 ++++++++++----
 src/perft.c       | 81 ++++++++++++++++++++++++++++++++++++-----------
 src/perft.h       |  2 +-
 src/position.c    | 33 ++++++++++++++++++-
 src/position.h    | 10 ++++--
 src/search.c      | 15 +++++++++
 src/search.h      |  1 +
 src/uci.c         | 29 ++++++++++++-----
 test/perft-test.c |  2 +-
 18 files changed, 183 insertions(+), 55 deletions(-)

diff --git a/Makefile b/Makefile
index cc829a3..181237c 100644
--- a/Makefile
+++ b/Makefile
@@ -415,7 +415,7 @@ TEST          += movedo-test perft-test tt-test
 PIECE_OBJS    := piece.o
 FEN_OBJS      := $(PIECE_OBJS) fen.o position.o bitboard.o board.o \
 	hq.o attack.o hash.o init.o util.o alloc.o move.o \
-	eval.o eval-defs.o eval-simple.o
+	eval.o eval-defs.o eval-simple.o hist.o
 BB_OBJS       := $(FEN_OBJS)
 MOVEGEN_OBJS  := $(BB_OBJS) move-gen.o
 ATTACK_OBJS   := $(MOVEGEN_OBJS)
diff --git a/src/brchess.c b/src/brchess.c
index 5b158a6..181519e 100644
--- a/src/brchess.c
+++ b/src/brchess.c
@@ -37,10 +37,10 @@ int main(int ac, char **av)
     pos_t *pos;
     int opt;
 
+    printf("brchess " VERSION "\n");
     init_all();
     pos = pos_new();
-    hist_link(pos);
-    printf("\nWelcome to brchess " VERSION "\nEngine ready.\n");
+    printf("Engine ready.\n");
 
     // size_t len = 0;
     // char *str = NULL;
diff --git a/src/chessdefs.h b/src/chessdefs.h
index 39b6822..25405de 100644
--- a/src/chessdefs.h
+++ b/src/chessdefs.h
@@ -85,9 +85,9 @@ typedef struct __movelist_s movelist_t;
 
 /* basic types
  */
-
 typedef u64 bitboard_t;
 typedef s16 eval_t;
+typedef s8 phase_t;
 
 /* forward enum definition is impossible in C11.
  * To simplify cross-dependancies, all important enum are moved here.
diff --git a/src/eval-defs.h b/src/eval-defs.h
index ab95263..bd3881c 100644
--- a/src/eval-defs.h
+++ b/src/eval-defs.h
@@ -14,7 +14,6 @@
 #ifndef EVAL_DEFS_H
 #define EVAL_DEFS_H
 
-
 #include "chessdefs.h"
 #include "piece.h"
 #include "eval.h"
@@ -26,7 +25,6 @@ enum {
     ENDGAME,
     PHASE_NB
 };
-typedef s16 phase_t;
 
 /* pieces weight in phase calculation.
  */
diff --git a/src/eval.c b/src/eval.c
index c736c7e..9f2fb64 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -30,7 +30,7 @@
  *
  * @return:
  */
-s16 calc_phase(pos_t *pos)
+phase_t calc_phase(pos_t *pos)
 {
     int phase = ALL_PHASE;
     phase -= P_PHASE * popcount64(pos->bb[WHITE][PAWN]   | pos->bb[BLACK][PAWN]);
diff --git a/src/eval.h b/src/eval.h
index 4a5eb07..2c2185a 100644
--- a/src/eval.h
+++ b/src/eval.h
@@ -19,7 +19,7 @@
 #include "chessdefs.h"
 #include "eval-defs.h"
 
-s16 calc_phase(pos_t *pos);
+phase_t calc_phase(pos_t *pos);
 
 eval_t eval_mobility(pos_t *pos, bool color);
 eval_t eval_square_control(pos_t *pos, bool color);
diff --git a/src/fen.c b/src/fen.c
index fc98d22..be7fe72 100644
--- a/src/fen.c
+++ b/src/fen.c
@@ -230,12 +230,12 @@ pos_t *fen2pos(pos_t *pos, const char *fen)
 
     /* 5) half moves since last capture or pawn move (50 moves rule)
      */
-    tmppos.clock_50 = 0;
+    tmppos.ply50 = 0;
     tmppos.plycount = 1;
     if (sscanf(cur, "%hd%n", &tmp, &consumed) != 1)
         goto end;                                 /* early end, ignore w/o err */
 
-    tmppos.clock_50 = tmp;
+    tmppos.ply50 = tmp;
     cur += consumed;
     SKIP_BLANK(cur);
 
@@ -350,7 +350,7 @@ char *pos2fen(const pos_t *pos, char *fen)
     /* 5) moves since last capture or pawn move (50 moves rule)
      * 6) current full move number, starting with 1
      */
-    sprintf(fen+cur, "%d %d", pos->clock_50,
+    sprintf(fen+cur, "%d %d", pos->ply50,
             1 + (pos->plycount - (pos->turn == BLACK)) / 2);
     return fen;
 }
diff --git a/src/hist.c b/src/hist.c
index 58314d3..1774a23 100644
--- a/src/hist.c
+++ b/src/hist.c
@@ -37,6 +37,16 @@ void hist_init(void)
     hist.state[0].prev = &hist.state[0];
 }
 
+/**
+ * hist_next() - get next history slot.
+ *
+ * return: @state_t next history slot.
+ */
+state_t *hist_next(void)
+{
+    return hist.state + hist.nstates++;
+}
+
 /**
  * hist_push() - add a state to hist list
  * @st:   &state_t to add
@@ -134,9 +144,10 @@ void hist_static_print(void)
 
     printf("UCI state history: ");
     while (true) {
-        printf("%s(#%lx) ",
+        printf("%s(#%lx r=%d) ",
                move_to_str(movestr, st->move, 0),
-               hash_short(st->key));
+               hash_short(st->key),
+               st->repcount);
         if (st == HIST_START)
             break;
         st = hist_prev(st);
@@ -154,9 +165,10 @@ void hist_print(pos_t *pos)
     state_t *st = &pos->state;
     printf("position states history: ");
     while (true) {
-        printf("%s(#%lx) ",
+        printf("%s(#%lx r=%d) ",
                move_to_str(movestr, st->move, 0),
-               hash_short(st->key));
+               hash_short(st->key),
+               st->repcount);
         if (st == HIST_START)
             break;
         st = hist_prev(st);
diff --git a/src/hist.h b/src/hist.h
index 01b4e3a..47cfec9 100644
--- a/src/hist.h
+++ b/src/hist.h
@@ -48,6 +48,7 @@ extern hist_t hist;
 #define HIST_START  (hist.state)
 
 void hist_init(void);
+state_t *hist_next(void);
 void hist_push(state_t *st); //, move_t *move);
 void hist_link(pos_t *pos);
 state_t *hist_pop(void);
diff --git a/src/move-do.c b/src/move-do.c
index 16cf79c..c64cd5a 100644
--- a/src/move-do.c
+++ b/src/move-do.c
@@ -24,6 +24,7 @@
 #include "position.h"
 #include "move-do.h"
 #include "hash.h"
+#include "hist.h"
 
 /**
  * move_do() - do move.
@@ -59,14 +60,16 @@ pos_t *move_do(pos_t *pos, const move_t move, state_t *state)
     hkey_t key = pos->key;
 
     *state = pos->state;                          /* save irreversible changes */
+    pos->prev = state;
 
     /* update key: switch turn, reset castling and ep */
     key ^= zobrist_turn;
     key ^= zobrist_castling[pos->castle];
     key ^= zobrist_ep[EP_ZOBRIST_IDX(pos->en_passant)];
 
-    ++pos->clock_50;
+    ++pos->ply50;
     ++pos->plycount;
+    ++pos->plyroot;
     pos->en_passant = SQUARE_NONE;
     pos->turn = them;
     pos->captured = captured;
@@ -80,7 +83,7 @@ pos_t *move_do(pos_t *pos, const move_t move, state_t *state)
     }
 
     if (captured != EMPTY) {
-        pos->clock_50 = 0;
+        pos->ply50 = 0;
         bug_on(pos->board[to] == EMPTY || COLOR(pos->captured) != them);
         key ^= zobrist_pieces[captured][to];
         pos_clr_sq(pos, to);                      /* clear square */
@@ -99,7 +102,7 @@ pos_t *move_do(pos_t *pos, const move_t move, state_t *state)
         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;
+        pos->ply50 = 0;
         if (from + up + up == to) {               /* if pawn double push, set e.p. */
             square_t ep = from + up;
             if (bb_pawn_attacks[us][ep] & pos->bb[them][PAWN]) {
@@ -151,6 +154,7 @@ pos_t *move_do(pos_t *pos, const move_t move, state_t *state)
 
     pos->key = key;
 
+    pos->repcount = pos_repcount(pos);
     zobrist_verify(pos);
 
     return pos;
@@ -209,6 +213,8 @@ pos_t *move_undo(pos_t *pos, const move_t move, const state_t *state)
 
     pos->state = *state;                          /* restore irreversible changes */
     pos->turn = us;
+    --pos->plycount;
+    --pos->plyroot;
     return pos;
 }
 
@@ -227,14 +233,16 @@ pos_t *move_do_alt(pos_t *pos, const move_t move, state_t *state)
     hkey_t key = pos->key;
 
     *state = pos->state;                          /* save irreversible changes */
+    pos->prev = state;
 
     /* update key: switch turn, reset castling and ep */
     key ^= zobrist_turn;
     key ^= zobrist_castling[pos->castle];
     key ^= zobrist_ep[EP_ZOBRIST_IDX(pos->en_passant)];
 
-    ++pos->clock_50;
+    ++pos->ply50;
     ++pos->plycount;
+    ++pos->plyroot;
     pos->en_passant = SQUARE_NONE;
     pos->turn = them;
     pos->captured = captured;
@@ -248,8 +256,7 @@ pos_t *move_do_alt(pos_t *pos, const move_t move, state_t *state)
     }
 
     if (captured != EMPTY) {
-        pos->clock_50 = 0;
-        //pos->captured = pos->board[to];           /* save capture info */
+        pos->ply50 = 0;
         bug_on(pos->board[to] == EMPTY || COLOR(pos->captured) != them);
         key ^= zobrist_pieces[captured][to];
         pos_clr_sq(pos, to);                      /* clear square */
@@ -268,7 +275,7 @@ pos_t *move_do_alt(pos_t *pos, const move_t move, state_t *state)
         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;
+        pos->ply50 = 0;
         if (from + up + up == to) {               /* if pawn double push, set e.p. */
             square_t ep = from + up;
             if (bb_pawn_attacks[us][ep] & pos->bb[them][PAWN]) {
@@ -320,6 +327,7 @@ pos_t *move_do_alt(pos_t *pos, const move_t move, state_t *state)
 
     pos->key = key;
 
+    pos->repcount = pos_repcount(pos);
     zobrist_verify(pos);
 
     return pos;
@@ -361,5 +369,7 @@ pos_t *move_undo_alt(pos_t *pos, const move_t move, const state_t *state)
 
     pos->state = *state;                          /* restore irreversible changes */
     pos->turn = us;
+    --pos->plycount;
+    --pos->plyroot;
     return pos;
 }
diff --git a/src/perft.c b/src/perft.c
index a05e285..970f1b3 100644
--- a/src/perft.c
+++ b/src/perft.c
@@ -40,7 +40,65 @@
  *
  * @return: total moves found at @depth level.
  */
-u64 perft(pos_t *pos, int depth, int ply, bool divide)
+static u64 do_perft(pos_t *pos, int depth)
+{
+    u64 subnodes = 0, nodes = 0;
+    movelist_t movelist;
+    move_t *move, *last;
+    state_t state;
+
+    pos_set_checkers_pinners_blockers(pos);
+    pos_legal(pos, pos_gen_pseudo(pos, &movelist));
+    if (depth == 1)
+        return movelist.nmoves;
+    last = movelist.move + movelist.nmoves;
+
+    for (move = movelist.move; move < last; ++move) {
+        move_do(pos, *move, &state);
+        if (depth == 2) {
+            movelist_t movelist2;
+            pos_set_checkers_pinners_blockers(pos);
+            subnodes = pos_legal(pos, pos_gen_pseudo(pos, &movelist2))->nmoves;
+        } else if (pos->plyroot >= 3) {
+            hentry_t *entry = tt_probe_perft(pos->key, depth);
+            if (entry != TT_MISS) {
+                subnodes = HASH_PERFT_VAL(entry->data);
+            } else {
+                subnodes = do_perft(pos, depth - 1);
+                tt_store_perft(pos->key, depth, subnodes);
+            }
+        } else {
+            subnodes = do_perft(pos, depth - 1);
+        }
+        move_undo(pos, *move, &state);
+        nodes += subnodes;
+    }
+
+    return nodes;
+}
+
+/**
+ * perft() - Perform perft on position
+ * @pos:    &position to search
+ * @depth:  Wanted depth.
+ * @ply:    current perft depth level (root = 1)
+ * @divide: output total for 1st level moves.
+ *
+ * Run perft on a position. This function displays the available moves at @depth
+ * level for each possible first move, and the total of moves.
+ *
+ * This version uses the algorithm:
+ *    if last depth
+ *      return 1;
+ *    gen legal moves
+ *    loop for legal move
+ *      do-move
+ *      perft (depth -1)
+ *      undo-move
+ *
+ * @return: total moves found at @depth level.
+ */
+u64 perft(pos_t *pos, int depth, bool divide)
 {
     u64 subnodes = 0, nodes = 0;
     movelist_t movelist;
@@ -56,30 +114,15 @@ u64 perft(pos_t *pos, int depth, int ply, bool divide)
             subnodes = 1;
         } else {
             move_do(pos, *move, &state);
-            if (depth == 2) {
-                movelist_t movelist2;
-                pos_set_checkers_pinners_blockers(pos);
-                subnodes = pos_legal(pos, pos_gen_pseudo(pos, &movelist2))->nmoves;
-            } else if (ply >= 3) {
-                hentry_t *entry = tt_probe_perft(pos->key, depth);
-                if (entry != TT_MISS) {
-                    subnodes = HASH_PERFT_VAL(entry->data);
-                } else {
-                    subnodes = perft(pos, depth - 1, ply + 1, divide);
-                    tt_store_perft(pos->key, depth, subnodes);
-                }
-            } else {
-                subnodes = perft(pos, depth - 1, ply + 1, divide);
-            }
+            subnodes = do_perft(pos, depth - 1);
             move_undo(pos, *move, &state);
         }
-        nodes += subnodes;
-        if (ply == 1 && divide) {
+        if (divide) {
             char movestr[8];
             printf("%s: %lu\n", move_to_str(movestr, *move, 0), subnodes);
         }
+        nodes += subnodes;
     }
-
     return nodes;
 }
 
diff --git a/src/perft.h b/src/perft.h
index 810475c..a574137 100644
--- a/src/perft.h
+++ b/src/perft.h
@@ -16,7 +16,7 @@
 
 #include "position.h"
 
-u64 perft(pos_t *pos, int depth, int ply, bool output);
+u64 perft(pos_t *pos, int depth,/* int ply,*/ bool divide);
 u64 perft_alt(pos_t *pos, int depth, int ply, bool output);
 
 #endif  /* PERFT_H */
diff --git a/src/position.c b/src/position.c
index 99b6d6c..40da984 100644
--- a/src/position.c
+++ b/src/position.c
@@ -108,6 +108,7 @@ pos_t *pos_clear(pos_t *pos)
 
     pos->king[WHITE] = SQUARE_NONE;
     pos->king[BLACK] = SQUARE_NONE;
+    pos->prev = HIST_START;
 
     return pos;
 }
@@ -130,7 +131,7 @@ bool pos_cmp(const pos_t *pos1, const pos_t *pos2)
 
     /* move_do/undo position state */
     if (_cmpf(key) || _cmpf(en_passant) || _cmpf(castle) ||
-        _cmpf(clock_50) || _cmpf(plycount) || _cmpf(captured))
+        _cmpf(ply50) || _cmpf(plycount) || _cmpf(captured))
         goto end;
 
     if (_cmpf(checkers) || _cmpf(pinners) || _cmpf(blockers))
@@ -180,6 +181,36 @@ bitboard_t pos_checkers(const pos_t *pos, const color_t color)
     return sq_attackers(pos, occ, pos->king[color], OPPONENT(color));
 }
 
+/**
+ * pos_repcount() - return position repetition count.
+ * @pos: &position to search
+ *
+ * Attention: positions before (and including) root position repcount is
+ * decreased by one. See do_moves() in uci.c.
+ *
+ * @return: The number of repetitions in history, zero otherwise.
+ */
+u8 pos_repcount(pos_t *pos)
+{
+    int c50 = pos->ply50;
+    state_t *st = &pos->state;
+    hkey_t key = pos->key;
+
+    st = hist_prev4(st);
+    //printf("is rep: START=%p ", HIST_START);
+    //printf("state=%p diff=%zd c50=%d k1=%#lx k2=%#lx\n",
+    //       st, st - HIST_START, c50, hash_short(pos->key), hash_short(st->key));
+
+    /* attention, what about root position ? Isn't it dangerous to compare with
+     * its key ? like: st->prev != HIST_START
+     */
+    for (; c50 >= 0 && st != HIST_START; st = hist_prev2(st), c50 -= 2) {
+        if (key == st->key)
+            return st->repcount + 1;
+    }
+    return false;
+}
+
 /**
  * pos_set_checkers_pinners_blockers() - calculate checkers, pinners and blockers.
  * @pos:   &position
diff --git a/src/position.h b/src/position.h
index 38a0e3c..1296ab4 100644
--- a/src/position.h
+++ b/src/position.h
@@ -27,6 +27,7 @@
 #include "piece.h"
 #include "move.h"
 #include "board.h"
+#include "eval-defs.h"
 
 typedef struct __pos_s {
     u64 node_count;                               /* evaluated nodes */
@@ -50,14 +51,14 @@ typedef struct __pos_s {
 
                         /* 16 bits */
                         move_t move;
-                        u16 plycount;             /* plies so far, start from 1 */
-                        s16 phase;
 
                         /* 8 bits */
                         square_t en_passant;
                         castle_rights_t castle;
                         piece_t captured;         /* only used in move_undo */
-                        u8 clock_50;
+                        phase_t phase;
+                        u8 ply50;
+                        u8 repcount;              /* repetition count */
         );
     eval_t eval;
     bitboard_t checkers;                          /* opponent checkers */
@@ -66,6 +67,8 @@ typedef struct __pos_s {
     piece_t board[BOARDSIZE];
     bitboard_t bb[2][PT_NB];                      /* bb[0][PAWN], bb[1][ALL_PIECES] */
     square_t king[2];                             /* dup with bb, faster retrieval */
+    u16 plycount;                                 /* plies in game, start from 1 */
+    u8 plyroot;                                   /* plies since search root. root=0 */
 } pos_t;
 
 typedef struct state_s state_t;
@@ -183,6 +186,7 @@ void pos_del(pos_t *pos);
 pos_t *pos_clear(pos_t *pos);
 bool pos_cmp(const pos_t *pos1, const pos_t *pos2);
 
+u8 pos_repcount(pos_t *pos);
 void pos_set_checkers_pinners_blockers(pos_t *pos);
 void pos_set_pinners_blockers(pos_t *pos);
 bitboard_t pos_checkers(const pos_t *pos, const color_t color);
diff --git a/src/search.c b/src/search.c
index 816c846..4e558d7 100644
--- a/src/search.c
+++ b/src/search.c
@@ -20,6 +20,21 @@
 #include "move-do.h"
 #include "search.h"
 #include "attack.h"
+#include "hist.h"
+
+/**
+ * is_draw() - check if position is draw by 50 or repetition rule.
+ * @pos: &position to search
+ *
+ * Note that states before (and including) root position state have
+ * their repcount decreased by one.
+ *
+ * @return: The @pos negamax evaluation.
+ */
+bool is_draw(pos_t *pos)
+{
+    return (pos->ply50 > 100 || pos->repcount);
+}
 
 /**
  * negamax() - search position negamax.
diff --git a/src/search.h b/src/search.h
index fa5766c..3b73978 100644
--- a/src/search.h
+++ b/src/search.h
@@ -16,6 +16,7 @@
 
 #include "position.h"
 
+bool is_draw(pos_t *pos);
 //eval_t negamax(pos_t *pos, int depth, int color);
 //eval_t pvs(pos_t *pos, int depth, int alpha, int beta, int color);
 
diff --git a/src/uci.c b/src/uci.c
index 7faed06..6054d6a 100644
--- a/src/uci.c
+++ b/src/uci.c
@@ -370,7 +370,7 @@ int do_position(pos_t *pos, char *arg)
     }
     /* link last position t history */
     //hist_pop();
-    hist_link(pos);
+    //hist_link(pos);
     return 1;
 }
 
@@ -378,8 +378,8 @@ int do_moves(__unused pos_t *pos, char *arg)
 {
     char *saveptr = NULL, *token, check[8];
     move_t move;
-    state_t state;
     movelist_t movelist;
+
     saveptr = NULL;
     token = strtok_r(arg, " ", &saveptr);
     while (token) {
@@ -395,13 +395,26 @@ int do_moves(__unused pos_t *pos, char *arg)
             return 1;
         }
         //printf("move: %s\n", move_to_str(check, move, 0));
-        hist_push(&pos->state);                   /* push previous state */
-        move_do(pos, move, &state);
-        pos_print(pos);
+        //hist_push(&pos->state);                   /* push previous state */
+        move_do(pos, move, hist_next());
+        printf("repet=%d\n", pos->repcount);
+        //if (is_repetition(pos))
+        //    printf("rep detected\n");
+        //else if(is_draw(pos))
+        //    printf("draw detected\n");
         hist_static_print();
         token = strtok_r(NULL, " ", &saveptr);
     }
-    //hist_static_print();
+    /* reset position root, and decrease history moves repcounts.
+     * TODO: Maybe use "ucinewgame" to decide when to perform this decrease ?
+     */
+    pos->plyroot = 0;
+    for (state_t *st = &pos->state; st != HIST_START; st = hist_prev(st)) {
+        //printf("adjust rep=%d->\n");
+        st->repcount = max(0, st->repcount - 1);
+    }
+    pos_print(pos);
+    hist_print(pos);
     return 1;
 }
 
@@ -429,7 +442,7 @@ int do_perft(__unused pos_t *pos, __unused char *arg)
     printf("perft: divide=%d alt=%d depth=%d\n", divide, alt, depth);
     if (depth > 0) {
         if (!alt)
-            perft(pos, depth, 1, divide);
+            perft(pos, depth, divide);
         else
             perft_alt(pos, depth, 1, divide);
     }
@@ -438,7 +451,7 @@ int do_perft(__unused pos_t *pos, __unused char *arg)
 
 int do_hist(__unused pos_t *pos, __unused char *arg)
 {
-    hist_static_print();
+    hist_print(pos);
     return 0;
 }
 
diff --git a/test/perft-test.c b/test/perft-test.c
index d8cab81..6bb0e9f 100644
--- a/test/perft-test.c
+++ b/test/perft-test.c
@@ -364,7 +364,7 @@ int main(int ac, char**av)
 
         if (run & 1) {
             clock_start(&clock);
-            my_count = perft(pos, depth, 1, divide);
+            my_count = perft(pos, depth, divide);
             ms = clock_elapsed_ms(&clock);
             if (!ms) {
                 res[0].skipped++;