Clean-up some shifting in space calculation (#1955)

protonspring · mcostalba · commit 691a287bfe7a · 2019-01-20T12:21:16.000+01:00
No functional change.
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
@@ -701,7 +701,8 @@ namespace {
     if (pos.non_pawn_material() < SpaceThreshold)
         return SCORE_ZERO;
 
-    constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
+    constexpr Color Them     = (Us == WHITE ? BLACK : WHITE);
+    constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
     constexpr Bitboard SpaceMask =
       Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
                   : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
@@ -713,8 +714,8 @@ namespace {
 
     // Find all squares which are at most three squares behind some friendly pawn
     Bitboard behind = pos.pieces(Us, PAWN);
-    behind |= (Us == WHITE ? behind >>  8 : behind <<  8);
-    behind |= (Us == WHITE ? behind >> 16 : behind << 16);
+    behind |= shift<Down>(behind);
+    behind |= shift<Down>(shift<Down>(behind));
 
     int bonus = popcount(safe) + popcount(behind & safe);
     int weight =  pos.count<ALL_PIECES>(Us)
