Use a formula for chain membership bonus

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index b74f0659b24a371a92a6184ce5c73a50ea57ae7c..91da8a7b0858cf748e7ba57231aabfa93b6f238a 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -51,17 +51,8 @@ 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) }};
 
-  // Pawn chain membership bonus by file
-  const Score ChainMember[FILE_NB][RANK_NB] = {
-    { S(0, 0), S(14, 0), S(16, 4), S(18,  9), S(56, 56), S(104, 208), S(236, 472) }, 
-    { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) }, 
-    { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) }, 
-    { S(0, 0), S(17, 0), S(19, 6), S(22, 11), S(66, 66), S(118, 236), S(254, 508) }, 
-    { S(0, 0), S(17, 0), S(19, 6), S(22, 11), S(66, 66), S(118, 236), S(254, 508) }, 
-    { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) }, 
-    { S(0, 0), S(16, 0), S(18, 5), S(20, 10), S(60, 60), S(108, 216), S(240, 480) }, 
-    { S(0, 0), S(14, 0), S(16, 4), S(18,  9), S(56, 56), S(104, 208), S(236, 472) }
-  }; 
+  // Pawn chain membership bonus by file and rank (initialized by formula)
+  Score ChainMember[FILE_NB][RANK_NB];
 
   // Candidate passed pawn bonus by rank
   const Score CandidatePassed[RANK_NB] = {
@@ -98,7 +89,6 @@ namespace {
     Bitboard b;
     Square s;
     File f;
-    Rank r;
     bool passed, isolated, doubled, opposed, chain, backward, candidate;
     Score value = SCORE_ZERO;
     const Square* pl = pos.list<PAWN>(Us);
@@ -119,7 +109,6 @@ namespace {
         assert(pos.piece_on(s) == make_piece(Us, PAWN));
 
         f = file_of(s);
-        r = relative_rank(Us, s);
 
         // This file cannot be semi-open
         e->semiopenFiles[Us] &= ~(1 << f);
@@ -184,11 +173,11 @@ namespace {
             value -= Backward[opposed][f];
 
         if (chain)
-            value += opposed ? ChainMember[f][r] / 2 : ChainMember[f][r];
+            value += ChainMember[f][relative_rank(Us, s)];
 
         if (candidate)
         {
-            value += CandidatePassed[r];
+            value += CandidatePassed[relative_rank(Us, s)];
 
             if (!doubled)
                 e->candidatePawns[Us] |= s;
@@ -202,6 +191,22 @@ namespace {
 
 namespace Pawns {
 
+/// init() initializes some tables by formula instead of hard-code their values
+
+void init() {
+
+  const int chainByFile[8] = { 1, 3, 3, 4, 4, 3, 3, 1 };
+  int bonus;
+
+  for (Rank r = RANK_1; r < RANK_8; ++r)
+      for (File f = FILE_A; f <= FILE_H; ++f)
+      {
+          bonus = r * (r-1) * (r-2) + chainByFile[f] * (r/2 + 1);
+          ChainMember[f][r] = make_score(bonus, bonus);
+      }
+}
+
+
 /// probe() takes a position object 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.
@@ -235,13 +240,13 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
   Rank rkUs, rkThem;
   File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
 
-  for (int f = kf - 1; f <= kf + 1; ++f)
+  for (File f = kf - File(1); f <= kf + File(1); ++f)
   {
-      b = ourPawns & FileBB[f];
+      b = ourPawns & file_bb(f);
       rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
       safety -= ShelterWeakness[rkUs];
 
-      b  = theirPawns & FileBB[f];
+      b  = theirPawns & file_bb(f);
       rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
       safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
   }