X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fpawns.cpp;h=d65b0418f0145f448c3d37dff8ecb7262c86fdaf;hp=718dd575957076d73e62b0bf47350619e826891c;hb=457ac26de5e2925c87bdc0169478d138074c50f8;hpb=1f40cd6d02374277abb5620d88d6fe58d7e9d6f7

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 718dd575..d65b0418 100644
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -92,7 +92,6 @@ 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);
@@ -113,13 +112,12 @@ namespace {
         assert(pos.piece_on(s) == make_piece(Us, PAWN));
 
         f = file_of(s);
-        r = rank_of(s);
 
         // This file cannot be semi-open
         e->semiopenFiles[Us] &= ~(1 << f);
 
         // Our rank plus previous one. Used for chain detection
-        b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
+        b = rank_bb(s) | rank_bb(s - pawn_push(Us));
 
         // Flag the pawn as passed, isolated, doubled or member of a pawn
         // chain (but not the backward one).
@@ -129,29 +127,25 @@ namespace {
         opposed  =   theirPawns & forward_bb(Us, s);
         passed   = !(theirPawns & passed_pawn_mask(Us, s));
 
-        // Test for backward pawn
-        backward = false;
-
+        // Test for backward pawn.
         // If the pawn is passed, isolated, or member of a pawn chain it cannot
         // be backward. If there are friendly pawns behind on adjacent files
         // or if can capture an enemy pawn it cannot be backward either.
-        if (   !(passed | isolated | chain)
-            && !(ourPawns & pawn_attack_span(Them, s))
-            && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
+        if (   (passed | isolated | chain)
+            || (ourPawns & pawn_attack_span(Them, s))
+            || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
+            backward = false;
+        else
         {
             // We now know that there are no friendly pawns beside or behind this
             // pawn on adjacent files. We now check whether the pawn is
             // backward by looking in the forward direction on the adjacent
-            // files, and seeing whether we meet a friendly or an enemy pawn first.
-            b = pos.attacks_from<PAWN>(s, Us);
-
-            // Note that we are sure to find something because pawn is not passed
-            // nor isolated, so loop is potentially infinite, but it isn't.
-            while (!(b & (ourPawns | theirPawns)))
-                b = shift_bb<Up>(b);
+            // files, and picking the closest pawn there.
+            b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
+            b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
 
-            // The friendly pawn needs to be at least two ranks closer than the
-            // enemy pawn in order to help the potentially backward pawn advance.
+            // If we have an enemy pawn in the same or next rank, the pawn is
+            // backward because it cannot advance without being captured.
             backward = (b | shift_bb<Up>(b)) & theirPawns;
         }
 
@@ -226,18 +220,16 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
   Bitboard ourPawns = b & pos.pieces(Us);
   Bitboard theirPawns = b & pos.pieces(Them);
   Rank rkUs, rkThem;
-  File kf = file_of(ksq);
-
-  kf = (kf == FILE_A) ? FILE_B : (kf == FILE_H) ? FILE_G : kf;
+  File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
 
   for (int f = kf - 1; f <= kf + 1; f++)
   {
       b = ourPawns & FileBB[f];
-      rkUs = b ? relative_rank(Us, Us == WHITE ? lsb(b) : msb(b)) : RANK_1;
+      rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
       safety -= ShelterWeakness[rkUs];
 
       b  = theirPawns & FileBB[f];
-      rkThem = b ? relative_rank(Us, Us == WHITE ? lsb(b) : msb(b)) : RANK_1;
+      rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
       safety -= StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
   }