Introduce and use SCORE_ZERO

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/evaluate.cpp

@@ -634,7 +634,7 @@ namespace {
     const Color Them = (Us == WHITE ? BLACK : WHITE);
 
     Bitboard b;
-    Score bonus = make_score(0, 0);
+    Score bonus = SCORE_ZERO;
 
     // Enemy pieces not defended by a pawn and under our attack
     Bitboard weakEnemies =  pos.pieces_of_color(Them)

src/pawns.cpp

@@ -185,7 +185,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
   Rank r;
   int bonus;
   bool passed, isolated, doubled, opposed, chain, backward, candidate;
-  Score value = make_score(0, 0);
+  Score value = SCORE_ZERO;
   const Square* ptr = pos.piece_list_begin(Us, PAWN);
 
   // Initialize pawn storm scores by giving bonuses for open files

src/position.cpp

@@ -1658,7 +1658,7 @@ Key Position::compute_material_key() const {
 /// updated by do_move and undo_move when the program is running in debug mode.
 Score Position::compute_value() const {
 
-  Score result = make_score(0, 0);
+  Score result = SCORE_ZERO;
   Bitboard b;
   Square s;
 

src/value.h

@@ -68,8 +68,9 @@ enum ScaleFactor {
 // Compiler is free to choose the enum type as long as can keep
 // its data, so ensure Score to be an integer type.
 enum Score {
-    ENSURE_32_BITS_SIZE_P =  (1 << 16),
-    ENSURE_32_BITS_SIZE_N = -(1 << 16)
+    SCORE_ZERO = 0,
+    SCORE_ENSURE_32_BITS_SIZE_P =  (1 << 16),
+    SCORE_ENSURE_32_BITS_SIZE_N = -(1 << 16)
 };
 
 ENABLE_OPERATORS_ON(Score);