From: Stefan Geschwentner <stgeschwentner@gmail.com>
Date: Thu, 19 Jan 2017 17:16:23 +0000 (+0100)
Subject: Candidate passed pawns
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=471f7a1b5c4da03a712da2ce079034de45b4c35b

Candidate passed pawns

Detect safe candidate passers.

STC: http://tests.stockfishchess.org/tests/view/5882395c0ebc5915193f78b3
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 53569 W: 9925 L: 9570 D: 34074

LTC: http://tests.stockfishchess.org/tests/view/5882b4fb0ebc5915193f78e2
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 77576 W: 10387 L: 10014 D: 57175

Bench: 5325829
---

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 6e33bb72..d9aae3d3 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -606,10 +606,11 @@ namespace {
   }
 
 
-  // evaluate_passed_pawns() evaluates the passed pawns of the given color
+  // evaluate_passer_pawns() evaluates the passed pawns and candidate passed
+  // pawns of the given color.
 
   template<Color Us, bool DoTrace>
-  Score evaluate_passed_pawns(const Position& pos, const EvalInfo& ei) {
+  Score evaluate_passer_pawns(const Position& pos, const EvalInfo& ei) {
 
     const Color Them = (Us == WHITE ? BLACK : WHITE);
 
@@ -622,7 +623,6 @@ namespace {
     {
         Square s = pop_lsb(&b);
 
-        assert(pos.pawn_passed(Us, s));
         assert(!(pos.pieces(PAWN) & forward_bb(Us, s)));
 
         bb = forward_bb(Us, s) & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
@@ -683,6 +683,11 @@ namespace {
         if (!pos.non_pawn_material(Them))
             ebonus += 20;
 
+        // Scale down bonus for candidate passers which need more than one pawn
+        // push to become passed.
+        if (!pos.pawn_passed(Us, s + pawn_push(Us)))
+            mbonus /= 2, ebonus /= 2;
+
         score += make_score(mbonus, ebonus) + PassedFile[file_of(s)];
     }
 
@@ -844,8 +849,8 @@ Value Eval::evaluate(const Position& pos) {
           - evaluate_threats<BLACK, DoTrace>(pos, ei);
 
   // Evaluate passed pawns, we need full attack information including king
-  score +=  evaluate_passed_pawns<WHITE, DoTrace>(pos, ei)
-          - evaluate_passed_pawns<BLACK, DoTrace>(pos, ei);
+  score +=  evaluate_passer_pawns<WHITE, DoTrace>(pos, ei)
+          - evaluate_passer_pawns<BLACK, DoTrace>(pos, ei);
 
   // Evaluate space for both sides, only during opening
   if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
diff --git a/src/pawns.cpp b/src/pawns.cpp
index 03b422f8..fb91afcb 100644
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -99,8 +99,9 @@ namespace {
     const Square Left  = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
 
     Bitboard b, neighbours, stoppers, doubled, supported, phalanx;
+    Bitboard lever, leverPush, connected;
     Square s;
-    bool opposed, lever, connected, backward;
+    bool opposed, backward;
     Score score = SCORE_ZERO;
     const Square* pl = pos.squares<PAWN>(Us);
     const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
@@ -129,6 +130,7 @@ namespace {
         opposed    = theirPawns & forward_bb(Us, s);
         stoppers   = theirPawns & passed_pawn_mask(Us, s);
         lever      = theirPawns & pawnAttacksBB[s];
+        leverPush  = theirPawns & pawnAttacksBB[s + Up];
         doubled    = ourPawns   & (s + Up);
         neighbours = ourPawns   & adjacent_files_bb(f);
         phalanx    = neighbours & rank_bb(s);
@@ -153,8 +155,13 @@ namespace {
         }
 
         // Passed pawns will be properly scored in evaluation because we need
-        // full attack info to evaluate them.
-        if (!stoppers && !(ourPawns & forward_bb(Us, s)))
+        // full attack info to evaluate them. Include also not passed pawns
+        // which could become passed after one or two pawn pushes when are
+        // not attacked more times than defended.
+        if (   !(stoppers ^ lever ^ leverPush)
+            && !(ourPawns & forward_bb(Us, s))
+            && popcount(supported) >= popcount(lever)
+            && popcount(phalanx)   >= popcount(leverPush))
             e->passedPawns[Us] |= s;
 
         // Score this pawn