Retire probe_dtz() from Tablebases

It is not needed in SF.

src/syzygy/tbprobe.cpp

@@ -505,7 +505,7 @@ public:
 
 // Given a position, produce a 64-bit material signature key. If the engine
 // supports such a key, it should equal the engine's key.
-Key get_key(Position& pos, bool mirror)
+Key get_key(const Position& pos, bool mirror)
 {
     Key key = 0;
 
@@ -1520,7 +1520,7 @@ WDLScore probe_wdl_table(Position& pos, int* success)
     }
 }
 
-int probe_dtz_table(Position& pos, int wdl, int *success)
+int probe_dtz_table(const Position& pos, int wdl, int *success)
 {
     uint64_t idx;
     int i, res;
@@ -1727,6 +1727,238 @@ WDLScore probe_ab(Position& pos, WDLScore alpha, WDLScore beta, int *success)
     }
 }
 
+int probe_dtz(Position& pos, int *success);
+
+// This routine treats a position with en passant captures as one without.
+int probe_dtz_no_ep(Position& pos, int *success)
+{
+    int dtz;
+
+    WDLScore wdl = probe_ab(pos, WDLHardLoss, WDLHardWin, success);
+
+    if (*success == 0) return 0;
+
+    if (wdl == WDLDraw) return 0;
+
+    if (*success == 2)
+        return wdl == WDLHardWin ? 1 : 101;
+
+    ExtMove stack[MAX_MOVES];
+    ExtMove *moves, *end = NULL;
+    StateInfo st;
+    CheckInfo ci(pos);
+
+    if (wdl > 0) {
+        // Generate at least all legal non-capturing pawn moves
+        // including non-capturing promotions.
+        if (!pos.checkers())
+            end = generate<NON_EVASIONS>(pos, stack);
+        else
+            end = generate<EVASIONS>(pos, stack);
+
+        for (moves = stack; moves < end; ++moves) {
+            Move move = moves->move;
+
+            if (   type_of(pos.moved_piece(move)) != PAWN
+                || pos.capture(move)
+                || !pos.legal(move, ci.pinned))
+                continue;
+
+            pos.do_move(move, st, pos.gives_check(move, ci));
+            WDLScore v = -probe_ab(pos, WDLHardLoss, -wdl + WDLSoftWin, success);
+            pos.undo_move(move);
+
+            if (*success == 0) return 0;
+
+            if (v == wdl)
+                return v == WDLHardWin ? 1 : 101;
+        }
+    }
+
+    dtz = 1 + probe_dtz_table(pos, wdl, success);
+
+    if (*success >= 0) {
+        if (wdl & 1) dtz += 100;
+
+        return wdl >= 0 ? dtz : -dtz;
+    }
+
+    if (wdl > 0) {
+        int best = 0xffff;
+
+        for (moves = stack; moves < end; ++moves) {
+            Move move = moves->move;
+
+            if (pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN
+                    || !pos.legal(move, ci.pinned))
+                continue;
+
+            pos.do_move(move, st, pos.gives_check(move, ci));
+            int v = -probe_dtz(pos, success);
+            pos.undo_move(move);
+
+            if (*success == 0)
+                return 0;
+
+            if (v > 0 && v + 1 < best)
+                best = v + 1;
+        }
+
+        return best;
+    } else {
+        int best = -1;
+
+        if (!pos.checkers())
+            end = generate<NON_EVASIONS>(pos, stack);
+        else
+            end = generate<EVASIONS>(pos, stack);
+
+        for (moves = stack; moves < end; ++moves) {
+            int v;
+            Move move = moves->move;
+
+            if (!pos.legal(move, ci.pinned))
+                continue;
+
+            pos.do_move(move, st, pos.gives_check(move, ci));
+
+            if (st.rule50 == 0) {
+                if (wdl == -2) v = -1;
+                else {
+                    v = probe_ab(pos, WDLSoftWin, WDLHardWin, success);
+                    v = (v == 2) ? 0 : -101;
+                }
+            } else {
+                v = -probe_dtz(pos, success) - 1;
+            }
+
+            pos.undo_move(move);
+
+            if (*success == 0)
+                return 0;
+
+            if (v < best)
+                best = v;
+        }
+
+        return best;
+    }
+}
+
+// Probe the DTZ table for a particular position.
+// If *success != 0, the probe was successful.
+// The return value is from the point of view of the side to move:
+//         n < -100 : loss, but draw under 50-move rule
+// -100 <= n < -1   : loss in n ply (assuming 50-move counter == 0)
+//         0        : draw
+//     1 < n <= 100 : win in n ply (assuming 50-move counter == 0)
+//   100 < n        : win, but draw under 50-move rule
+//
+// The return value n can be off by 1: a return value -n can mean a loss
+// in n+1 ply and a return value +n can mean a win in n+1 ply. This
+// cannot happen for tables with positions exactly on the "edge" of
+// the 50-move rule.
+//
+// This implies that if dtz > 0 is returned, the position is certainly
+// a win if dtz + 50-move-counter <= 99. Care must be taken that the engine
+// picks moves that preserve dtz + 50-move-counter <= 99.
+//
+// If n = 100 immediately after a capture or pawn move, then the position
+// is also certainly a win, and during the whole phase until the next
+// capture or pawn move, the inequality to be preserved is
+// dtz + 50-movecounter <= 100.
+//
+// In short, if a move is available resulting in dtz + 50-move-counter <= 99,
+// then do not accept moves leading to dtz + 50-move-counter == 100.
+//
+int probe_dtz(Position& pos, int *success)
+{
+    *success = 1;
+    int v = probe_dtz_no_ep(pos, success);
+
+    if (pos.ep_square() == SQ_NONE)
+        return v;
+
+    if (*success == 0)
+        return 0;
+
+    // Now handle en passant.
+    int v1 = -3;
+
+    ExtMove stack[MAX_MOVES];
+    ExtMove *moves, *end;
+    StateInfo st;
+
+    if (!pos.checkers())
+        end = generate<CAPTURES>(pos, stack);
+    else
+        end = generate<EVASIONS>(pos, stack);
+
+    CheckInfo ci(pos);
+
+    for (moves = stack; moves < end; ++moves) {
+        Move capture = moves->move;
+
+        if (type_of(capture) != ENPASSANT
+                || !pos.legal(capture, ci.pinned))
+            continue;
+
+        pos.do_move(capture, st, pos.gives_check(capture, ci));
+        WDLScore v0 = -probe_ab(pos, WDLHardLoss, WDLHardWin, success);
+        pos.undo_move(capture);
+
+        if (*success == 0)
+            return 0;
+
+        if (v0 > v1) v1 = v0;
+    }
+
+    if (v1 > -3) {
+        v1 = wdl_to_dtz[v1 + 2];
+
+        if (v < -100) {
+            if (v1 >= 0)
+                v = v1;
+        } else if (v < 0) {
+            if (v1 >= 0 || v1 < -100)
+                v = v1;
+        } else if (v > 100) {
+            if (v1 > 0)
+                v = v1;
+        } else if (v > 0) {
+            if (v1 == 1)
+                v = v1;
+        } else if (v1 >= 0) {
+            v = v1;
+        } else {
+            for (moves = stack; moves < end; ++moves) {
+                Move move = moves->move;
+
+                if (type_of(move) == ENPASSANT) continue;
+
+                if (pos.legal(move, ci.pinned))
+                    break;
+            }
+
+            if (moves == end && !pos.checkers()) {
+                end = generate<QUIETS>(pos, end);
+
+                for (; moves < end; ++moves) {
+                    Move move = moves->move;
+
+                    if (pos.legal(move, ci.pinned))
+                        break;
+                }
+            }
+
+            if (moves == end)
+                v = v1;
+        }
+    }
+
+    return v;
+}
+
 } // namespace
 
 void Tablebases::free()
@@ -1895,236 +2127,6 @@ WDLScore Tablebases::probe_wdl(Position& pos, int *success)
     return v;
 }
 
-// This routine treats a position with en passant captures as one without.
-static int probe_dtz_no_ep(Position& pos, int *success)
-{
-    int dtz;
-
-    WDLScore wdl = probe_ab(pos, WDLHardLoss, WDLHardWin, success);
-
-    if (*success == 0) return 0;
-
-    if (wdl == WDLDraw) return 0;
-
-    if (*success == 2)
-        return wdl == WDLHardWin ? 1 : 101;
-
-    ExtMove stack[MAX_MOVES];
-    ExtMove *moves, *end = NULL;
-    StateInfo st;
-    CheckInfo ci(pos);
-
-    if (wdl > 0) {
-        // Generate at least all legal non-capturing pawn moves
-        // including non-capturing promotions.
-        if (!pos.checkers())
-            end = generate<NON_EVASIONS>(pos, stack);
-        else
-            end = generate<EVASIONS>(pos, stack);
-
-        for (moves = stack; moves < end; ++moves) {
-            Move move = moves->move;
-
-            if (   type_of(pos.moved_piece(move)) != PAWN
-                || pos.capture(move)
-                || !pos.legal(move, ci.pinned))
-                continue;
-
-            pos.do_move(move, st, pos.gives_check(move, ci));
-            WDLScore v = -probe_ab(pos, WDLHardLoss, -wdl + WDLSoftWin, success);
-            pos.undo_move(move);
-
-            if (*success == 0) return 0;
-
-            if (v == wdl)
-                return v == WDLHardWin ? 1 : 101;
-        }
-    }
-
-    dtz = 1 + probe_dtz_table(pos, wdl, success);
-
-    if (*success >= 0) {
-        if (wdl & 1) dtz += 100;
-
-        return wdl >= 0 ? dtz : -dtz;
-    }
-
-    if (wdl > 0) {
-        int best = 0xffff;
-
-        for (moves = stack; moves < end; ++moves) {
-            Move move = moves->move;
-
-            if (pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN
-                    || !pos.legal(move, ci.pinned))
-                continue;
-
-            pos.do_move(move, st, pos.gives_check(move, ci));
-            int v = -Tablebases::probe_dtz(pos, success);
-            pos.undo_move(move);
-
-            if (*success == 0)
-                return 0;
-
-            if (v > 0 && v + 1 < best)
-                best = v + 1;
-        }
-
-        return best;
-    } else {
-        int best = -1;
-
-        if (!pos.checkers())
-            end = generate<NON_EVASIONS>(pos, stack);
-        else
-            end = generate<EVASIONS>(pos, stack);
-
-        for (moves = stack; moves < end; ++moves) {
-            int v;
-            Move move = moves->move;
-
-            if (!pos.legal(move, ci.pinned))
-                continue;
-
-            pos.do_move(move, st, pos.gives_check(move, ci));
-
-            if (st.rule50 == 0) {
-                if (wdl == -2) v = -1;
-                else {
-                    v = probe_ab(pos, WDLSoftWin, WDLHardWin, success);
-                    v = (v == 2) ? 0 : -101;
-                }
-            } else {
-                v = -Tablebases::probe_dtz(pos, success) - 1;
-            }
-
-            pos.undo_move(move);
-
-            if (*success == 0)
-                return 0;
-
-            if (v < best)
-                best = v;
-        }
-
-        return best;
-    }
-}
-
-// Probe the DTZ table for a particular position.
-// If *success != 0, the probe was successful.
-// The return value is from the point of view of the side to move:
-//         n < -100 : loss, but draw under 50-move rule
-// -100 <= n < -1   : loss in n ply (assuming 50-move counter == 0)
-//         0        : draw
-//     1 < n <= 100 : win in n ply (assuming 50-move counter == 0)
-//   100 < n        : win, but draw under 50-move rule
-//
-// The return value n can be off by 1: a return value -n can mean a loss
-// in n+1 ply and a return value +n can mean a win in n+1 ply. This
-// cannot happen for tables with positions exactly on the "edge" of
-// the 50-move rule.
-//
-// This implies that if dtz > 0 is returned, the position is certainly
-// a win if dtz + 50-move-counter <= 99. Care must be taken that the engine
-// picks moves that preserve dtz + 50-move-counter <= 99.
-//
-// If n = 100 immediately after a capture or pawn move, then the position
-// is also certainly a win, and during the whole phase until the next
-// capture or pawn move, the inequality to be preserved is
-// dtz + 50-movecounter <= 100.
-//
-// In short, if a move is available resulting in dtz + 50-move-counter <= 99,
-// then do not accept moves leading to dtz + 50-move-counter == 100.
-//
-int Tablebases::probe_dtz(Position& pos, int *success)
-{
-    *success = 1;
-    int v = probe_dtz_no_ep(pos, success);
-
-    if (pos.ep_square() == SQ_NONE)
-        return v;
-
-    if (*success == 0)
-        return 0;
-
-    // Now handle en passant.
-    int v1 = -3;
-
-    ExtMove stack[MAX_MOVES];
-    ExtMove *moves, *end;
-    StateInfo st;
-
-    if (!pos.checkers())
-        end = generate<CAPTURES>(pos, stack);
-    else
-        end = generate<EVASIONS>(pos, stack);
-
-    CheckInfo ci(pos);
-
-    for (moves = stack; moves < end; ++moves) {
-        Move capture = moves->move;
-
-        if (type_of(capture) != ENPASSANT
-                || !pos.legal(capture, ci.pinned))
-            continue;
-
-        pos.do_move(capture, st, pos.gives_check(capture, ci));
-        WDLScore v0 = -probe_ab(pos, WDLHardLoss, WDLHardWin, success);
-        pos.undo_move(capture);
-
-        if (*success == 0)
-            return 0;
-
-        if (v0 > v1) v1 = v0;
-    }
-
-    if (v1 > -3) {
-        v1 = wdl_to_dtz[v1 + 2];
-
-        if (v < -100) {
-            if (v1 >= 0)
-                v = v1;
-        } else if (v < 0) {
-            if (v1 >= 0 || v1 < -100)
-                v = v1;
-        } else if (v > 100) {
-            if (v1 > 0)
-                v = v1;
-        } else if (v > 0) {
-            if (v1 == 1)
-                v = v1;
-        } else if (v1 >= 0) {
-            v = v1;
-        } else {
-            for (moves = stack; moves < end; ++moves) {
-                Move move = moves->move;
-
-                if (type_of(move) == ENPASSANT) continue;
-
-                if (pos.legal(move, ci.pinned))
-                    break;
-            }
-
-            if (moves == end && !pos.checkers()) {
-                end = generate<QUIETS>(pos, end);
-
-                for (; moves < end; ++moves) {
-                    Move move = moves->move;
-
-                    if (pos.legal(move, ci.pinned))
-                        break;
-                }
-            }
-
-            if (moves == end)
-                v = v1;
-        }
-    }
-
-    return v;
-}
-
 // Check whether there has been at least one repetition of positions
 // since the last capture or pawn move.
 static int has_repeated(StateInfo *st)
@@ -2182,14 +2184,14 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, Value&
 
         if (!v) {
             if (st.rule50 != 0) {
-                v = -Tablebases::probe_dtz(pos, &success);
+                v = -probe_dtz(pos, &success);
 
                 if (v > 0)
                     ++v;
                 else if (v < 0)
                     --v;
             } else {
-                v = -Tablebases::probe_wdl(pos, &success);
+                v = -probe_wdl(pos, &success);
                 v = wdl_to_dtz[v + 2];
             }
         }

src/syzygy/tbprobe.h

@@ -18,7 +18,6 @@ extern int MaxCardinality;
 void init(const std::string& paths);
 void free();
 WDLScore probe_wdl(Position& pos, int* success);
-int probe_dtz(Position& pos, int* success);
 bool root_probe(Position& pos, Search::RootMoves& rootMoves, Value& score);
 bool root_probe_wdl(Position& pos, Search::RootMoves& rootMoves, Value& score);