Speed-up some arrays reading

This patch removes the empty rows at the beginning and at the end of
MobilityBonus[] and Protector[] arrays:

• reducing the size of MobilityBonus from 768 bytes to 512 bytes
• reducing the size of Protector from 1024 to 512 bytes

Also adds some comments and cleaner code for the arrays in pawns.cpp

No speed penalty (measured speed-up of 0.4%).

No functional change.

Closes #1018

src/evaluate.cpp

@@ -115,10 +115,9 @@ namespace {
   #define V(v) Value(v)
   #define S(mg, eg) make_score(mg, eg)
 
-  // MobilityBonus[PieceType][attacked] contains bonuses for middle and end game,
+  // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
   // indexed by piece type and number of attacked squares in the mobility area.
-  const Score MobilityBonus[][32] = {
+  const Score MobilityBonus[4][32] = {
-    {}, {},
     { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S(  6,  5), S( 14, 12), // Knights
       S( 22, 26), S( 29, 29), S( 36, 29) },
     { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
@@ -181,10 +180,9 @@ namespace {
     S(-20,-12), S( 1, -8), S( 2, 10), S(  9, 10)
   };
   
-  // Protector[PieceType][distance] contains a protecting bonus for our king,
+  // Protector[PieceType-2][distance] contains a protecting bonus for our king,
   // indexed by piece type and distance between the piece and the king.
-  const Score Protector[PIECE_TYPE_NB][8] = {
+  const Score Protector[4][8] = {
-    {}, {},
     { S(0, 0), S( 7, 9), S( 7, 1), S( 1, 5), S(-10,-4), S( -1,-4), S( -7,-3), S(-16,-10) }, // Knight
     { S(0, 0), S(11, 8), S(-7,-1), S(-1,-2), S( -1,-7), S(-11,-3), S( -9,-1), S(-16, -1) }, // Bishop
     { S(0, 0), S(10, 0), S(-2, 2), S(-5, 4), S( -6, 2), S(-14,-3), S( -2,-9), S(-12, -7) }, // Rook
@@ -303,10 +301,10 @@ namespace {
 
         int mob = popcount(b & ei.mobilityArea[Us]);
 
-        mobility[Us] += MobilityBonus[Pt][mob];
+        mobility[Us] += MobilityBonus[Pt-2][mob];
         
         // Bonus for this piece as a king protector
-        score += Protector[Pt][distance(s, pos.square<KING>(Us))];
+        score += Protector[Pt-2][distance(s, pos.square<KING>(Us))];
 
         if (Pt == BISHOP || Pt == KNIGHT)
         {

src/pawns.cpp

@@ -256,12 +256,13 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
       b  = theirPawns & file_bb(f);
       Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
 
-      safety -=  ShelterWeakness[std::min(f, FILE_H - f)][rkUs]
+      int d = std::min(f, FILE_H - f);
+      safety -=  ShelterWeakness[d][rkUs]
                + StormDanger
                  [f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing  :
                   rkUs   == RANK_1                                          ? Unopposed :
                   rkThem == rkUs + 1                                        ? BlockedByPawn  : Unblocked]
-                 [std::min(f, FILE_H - f)][rkThem];
+                 [d][rkThem];
   }
 
   return safety;