From: protonspring <mike@whiteley.org>
Date: Mon, 20 Aug 2018 16:29:46 +0000 (-0600)
Subject: make DistanceRing more consistent
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=8a4821923ac6860c791185a6d25c60ad0391739f;hp=6307fd08e6e8c315802301fd35b22ca2a67071a9;ds=inline

make DistanceRing more consistent

This is a non-functional change. By pre-incrementing minKingPawnDistance
instead of post-incrementing, we can remove this -1.

This also makes DistanceRing more consistent with the rest of stockfish
since it now holds an actual "distance" instead of a less natural distance-1.

In current master, PseudoAttacks[KING][ksq] == DistanceRingBB[ksq][0]
With this patch, it will be PseudoAttacks[KING][ksq] == DistanceRingBB[ksq][1]
ie squares at distance 1 from the king. This is more natural use of distance.

The current array size DistanceRingBB[SQUARE_NB][8] is still OK with the new
definition, because maximum distance between two squares on a chess board is
seven (for example Kh1 and a8).

No functional change.
---

diff --git a/src/bitboard.cpp b/src/bitboard.cpp
index b3aeed85..4e2778a9 100644
--- a/src/bitboard.cpp
+++ b/src/bitboard.cpp
@@ -116,7 +116,7 @@ void Bitboards::init() {
           if (s1 != s2)
           {
               SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
-              DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
+              DistanceRingBB[s1][SquareDistance[s1][s2]] |= s2;
           }
 
   int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
diff --git a/src/pawns.cpp b/src/pawns.cpp
index 7cc71ca6..5048d4f1 100644
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -245,7 +245,7 @@ Score Entry::do_king_safety(const Position& pos, Square ksq) {
 
   Bitboard pawns = pos.pieces(Us, PAWN);
   if (pawns)
-      while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
+      while (!(DistanceRingBB[ksq][++minKingPawnDistance] & pawns)) {}
 
   Value bonus = evaluate_shelter<Us>(pos, ksq);