Consolidate pawn storm types

Simplification: the Unopposed and Unblocked pawn storm types are mathematically
similar enough to combine with no Elo loss. This reduces the pawn storm types
to BlockedByPawn and UnBlocked.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 116869 W: 23549 L: 23605 D: 69715
http://tests.stockfishchess.org/tests/view/5af2def90ebc5968e6523f82

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 39912 W: 6090 L: 5998 D: 27824
http://tests.stockfishchess.org/tests/view/5af3b2e20ebc5968e6524013

Closes https://github.com/official-stockfish/Stockfish/pull/1592

Bench: 5244314

diff --git a/src/pawns.cpp b/src/pawns.cpp
index b8a002428d5a1a6cc4e9024438a792267b0a7d10..2378b5325dd05df41e1c319a25462021fca3fb1c 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -53,21 +53,17 @@ namespace {
   };
 
   // Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
-  // For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has
-  // no pawn on the given file, or their pawn is behind our king.
+  // For the unblocked case, RANK_1 = 0 is used when opponent has no pawn on the
+  // given file, or their pawn is behind our king.
   constexpr Value StormDanger[][4][RANK_NB] = {
-    { { V(11),  V( 79), V(132), V( 68), V( 33) },  // Unopposed
-      { V( 4),  V(104), V(155), V(  4), V( 21) },
-      { V(-7),  V( 59), V(142), V( 45), V( 30) },
-      { V( 0),  V( 62), V(113), V( 43), V( 13) } },
+    { { V(25),  V( 79), V(107), V( 51), V( 27) },  // UnBlocked
+      { V(15),  V( 45), V(131), V(  8), V( 25) },
+      { V( 0),  V( 42), V(118), V( 56), V( 27) },
+      { V( 3),  V( 54), V(110), V( 55), V( 26) } },
     { { V( 0),  V(  0), V( 37), V(  5), V(-48) },  // BlockedByPawn
       { V( 0),  V(  0), V( 68), V(-12), V( 13) },
       { V( 0),  V(  0), V(111), V(-25), V( -3) },
-      { V( 0),  V(  0), V(108), V( 14), V( 21) } },
-    { { V(38),  V( 78), V( 83), V( 35), V( 22) },  // Unblocked
-      { V(33),  V(-15), V(108), V( 12), V( 28) },
-      { V( 8),  V( 25), V( 94), V( 68), V( 25) },
-      { V( 6),  V( 48), V(120), V( 68), V( 40) } }
+      { V( 0),  V(  0), V(108), V( 14), V( 21) } }
   };
 
   #undef S
@@ -212,7 +208,7 @@ Entry* probe(const Position& pos) {
 template<Color Us>
 Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
 
-  enum { Unopposed, BlockedByPawn, Unblocked };
+  enum { UnBlocked, BlockedByPawn };
   constexpr Color     Them = (Us == WHITE ? BLACK : WHITE);
   constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
   constexpr Bitboard  BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
@@ -224,22 +220,22 @@ Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
   Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
 
   if (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq)
-      safety += 374;
+      safety += Value(374);
 
   File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
   for (File f = File(center - 1); f <= File(center + 1); ++f)
   {
       b = ourPawns & file_bb(f);
-      Rank rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
+      int ourRank = b ? relative_rank(Us, backmost_sq(Us, b)) : 0;
 
       b = theirPawns & file_bb(f);
-      Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
+      int theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : 0;
 
       int d = std::min(f, ~f);
-      safety +=  ShelterStrength[d][rkUs]
-               - StormDanger[rkUs == RANK_1     ? Unopposed     :
-                             rkUs == rkThem - 1 ? BlockedByPawn : Unblocked]
-                            [d][rkThem];
+
+      safety += ShelterStrength[d][ourRank];
+      if (ourRank || theirRank)
+         safety -= StormDanger[ourRank && (ourRank == theirRank - 1) ? BlockedByPawn : UnBlocked][d][theirRank];
   }
 
   return safety;