Space bonus and number of blocked pawns

This patch refines the recently introduced interaction between
the space bonus and the number of blocked pawns in a position.

* pawns count as blocked also if their push square is attacked by 2 enemy pawns;
* overall dependence is stronger as well as offset;
* bonus increase is capped at 9 blocked pawns in position;

passed STC
https://tests.stockfishchess.org/tests/view/5e94560663d105aebbab243d
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 29500 W: 5842 L: 5603 D: 18055
Ptnml(0-2): 504, 3443, 6677, 3562, 564

passed LTC
https://tests.stockfishchess.org/tests/view/5e95b383c2aaa99f75d1a14d
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 63504 W: 8329 L: 7974 D: 47201
Ptnml(0-2): 492, 5848, 18720, 6197, 495

closes https://github.com/official-stockfish/Stockfish/pull/2631

bench 4956028

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index cd535d885fc2e617d42c90588f2127f69e6fedfd..8feedfebad7d522cd80b33d420e35e61a0867fa7 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -695,7 +695,7 @@ namespace {
     behind |= shift<Down+Down>(behind);
 
     int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
-    int weight = pos.count<ALL_PIECES>(Us) - 2 + pe->blocked_count() / 2;
+    int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
     Score score = make_score(bonus * weight * weight / 16, 0);
 
     if (T)

diff --git a/src/pawns.cpp b/src/pawns.cpp
index a2063a8f8323cd9ad420e81d8cfe60cd93099ff6..75e6ad7a7dfc9f50b675c9b0eb6c8b4a10f308f4 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -106,7 +106,7 @@ namespace {
         phalanx    = neighbours & rank_bb(s);
         support    = neighbours & rank_bb(s - Up);
 
-        e->blockedCount[Us] += bool(blocked);
+        e->blockedCount[Us] += blocked || more_than_one(leverPush);
 
         // A pawn is backward when it is behind all pawns of the same color on
         // the adjacent files and cannot safely advance.