Retire PawnsFileSpan

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 4693e1584f5b2161573fd42ff19643791feeef20..3634f95746796afef7ab904856629b59d2c970fa 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -49,17 +49,14 @@ namespace {
   { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
     S(33, 31), S(33, 31), S(29, 31), S(20, 28) } };
 
-  // Connected bonus by rank
-  const int Connected[RANK_NB] = {0, 6, 15, 10, 57, 75, 135, 258};
+  // Connected pawn bonus by opposed, phalanx flags and rank
+  Score Connected[2][2][RANK_NB];
 
   // Levers bonus by rank
   const Score Lever[RANK_NB] = {
     S( 0, 0), S( 0, 0), S(0, 0), S(0, 0),
     S(20,20), S(40,40), S(0, 0), S(0, 0) };
 
-  // Bonus for file distance of the two outermost pawns
-  const Score PawnsFileSpan = S(0, 15);
-
   // Unsupported pawn penalty
   const Score UnsupportedPawnPenalty = S(20, 10);
 
@@ -89,9 +86,9 @@ namespace {
     const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
     const Square Left  = (Us == WHITE ? DELTA_NW : DELTA_SE);
 
-    Bitboard b, p, doubled;
+    Bitboard b, p, doubled, connected;
     Square s;
-    bool passed, isolated, opposed, connected, backward, unsupported, lever;
+    bool passed, isolated, opposed, phalanx, backward, unsupported, lever;
     Score value = SCORE_ZERO;
     const Square* pl = pos.list<PAWN>(Us);
     const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
@@ -111,7 +108,6 @@ namespace {
     {
         assert(pos.piece_on(s) == make_piece(Us, PAWN));
 
-        Rank r = rank_of(s), rr = relative_rank(Us, s);
         File f = file_of(s);
 
         // This file cannot be semi-open
@@ -120,12 +116,10 @@ namespace {
         // Previous rank
         p = rank_bb(s - pawn_push(Us));
 
-        // Our rank plus previous one
-        b = rank_bb(s) | p;
-
         // Flag the pawn as passed, isolated, doubled,
         // unsupported or connected (but not the backward one).
-        connected   =   ourPawns   & adjacent_files_bb(f) & b;
+        connected   =   ourPawns   & adjacent_files_bb(f) & (rank_bb(s) | p);
+        phalanx     =   connected  & rank_bb(s);
         unsupported = !(ourPawns   & adjacent_files_bb(f) & p);
         isolated    = !(ourPawns   & adjacent_files_bb(f));
         doubled     =   ourPawns   & forward_bb(Us, s);
@@ -176,24 +170,16 @@ namespace {
         if (backward)
             value -= Backward[opposed][f];
 
-        if (connected) {
-            int bonus = Connected[rr];
-            if (ourPawns & adjacent_files_bb(f) & rank_bb(r))
-                bonus += (Connected[rr+1] - Connected[rr]) / 2;
-            value += make_score(bonus / 2, bonus >> opposed);
-        }
+        if (connected)
+            value += Connected[opposed][phalanx][relative_rank(Us, s)];
 
         if (lever)
-            value += Lever[rr];
+            value += Lever[relative_rank(Us, s)];
     }
 
     b = e->semiopenFiles[Us] ^ 0xFF;
     e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
 
-    // In endgame it's better to have pawns on both wings. So give a bonus according
-    // to file distance between left and right outermost pawns.
-    value += PawnsFileSpan * e->pawnSpan[Us];
-
     return value;
   }
 
@@ -201,6 +187,24 @@ namespace {
 
 namespace Pawns {
 
+/// init() initializes some tables used by evaluation. Instead of hard-coded
+/// tables, when makes sense, we prefer to calculate them with a formula to
+/// reduce independent parameters and to allow easier tuning and better insight.
+
+void init()
+{
+  static const int Seed[RANK_NB] = { 0, 6, 15, 10, 57, 75, 135, 258 };
+
+  for (int opposed = 0; opposed <= 1; ++opposed)
+      for (int phalanx = 0; phalanx <= 1; ++phalanx)
+          for (Rank r = RANK_2; r < RANK_8; ++r)
+          {
+              int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
+              Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
+          }
+}
+
+
 /// probe() takes a position as input, computes a Entry object, and returns a
 /// pointer to it. The result is also stored in a hash table, so we don't have
 /// to recompute everything when the same pawn structure occurs again.