Rename first_1 / last_1 in lsb / msb

It seems more accurate: lsb is clear while 'first
bit' depends from where you look at the bitboard.

And fix compile in case of 64 bits platforms that
do not use BSFQ intrinsics.

No functional change.

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

src/bitbase.cpp

@@ -196,8 +196,8 @@ namespace {
 
     while (b)
     {
-        r |= Us == WHITE ? db[index(pop_1st_bit(&b), bksq, psq, BLACK)]
+        r |= Us == WHITE ? db[index(pop_lsb(&b), bksq, psq, BLACK)]
-                         : db[index(wksq, pop_1st_bit(&b), psq, WHITE)];
+                         : db[index(wksq, pop_lsb(&b), psq, WHITE)];
 
         if (Us == WHITE && (r & WIN))
             return WIN;

src/bitboard.cpp

@@ -69,40 +69,35 @@ namespace {
                    Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
 }
 
-/// first_1() finds the least significant nonzero bit in a nonzero bitboard.
+/// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
-/// pop_1st_bit() finds and clears the least significant nonzero bit in a
+/// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
-/// nonzero bitboard.
 
-#if defined(IS_64BIT) && !defined(USE_BSFQ)
+#if !defined(USE_BSFQ)
 
-Square first_1(Bitboard b) {
+Square lsb(Bitboard b) {
-  return Square(BSFTable[((b & -b) * 0x218A392CD3D5DBFULL) >> 58]);
-}
 
-Square pop_1st_bit(Bitboard* b) {
+  if (Is64Bit)
-  Bitboard bb = *b;
+      return Square(BSFTable[((b & -b) * 0x218A392CD3D5DBFULL) >> 58]);
-  *b &= (*b - 1);
-  return Square(BSFTable[((bb & -bb) * 0x218A392CD3D5DBFULL) >> 58]);
-}
 
-#elif !defined(USE_BSFQ)
-
-Square first_1(Bitboard b) {
   b ^= (b - 1);
   uint32_t fold = unsigned(b) ^ unsigned(b >> 32);
   return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
 }
 
-Square pop_1st_bit(Bitboard* b) {
+Square pop_lsb(Bitboard* b) {
 
   Bitboard bb = *b;
   *b = bb & (bb - 1);
+
+  if (Is64Bit)
+      return Square(BSFTable[((bb & -bb) * 0x218A392CD3D5DBFULL) >> 58]);
+
   bb ^= (bb - 1);
   uint32_t fold = unsigned(bb) ^ unsigned(bb >> 32);
   return Square(BSFTable[(fold * 0x783A9B23) >> 26]);
 }
 
-Square last_1(Bitboard b) {
+Square msb(Bitboard b) {
 
   unsigned b32;
   int result = 0;

src/bitboard.h

@@ -221,51 +221,52 @@ inline Bitboard attacks_bb(Square s, Bitboard occ) {
 }
 
 
-/// first_1() finds the least significant nonzero bit in a nonzero bitboard.
+/// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
-/// pop_1st_bit() finds and clears the least significant nonzero bit in a
+/// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
-/// nonzero bitboard.
 
 #if defined(USE_BSFQ)
 
-#if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
+#  if defined(_MSC_VER) && !defined(__INTEL_COMPILER)
 
-FORCE_INLINE Square first_1(Bitboard b) {
+FORCE_INLINE Square lsb(Bitboard b) {
   unsigned long index;
   _BitScanForward64(&index, b);
   return (Square) index;
 }
 
-FORCE_INLINE Square last_1(Bitboard b) {
+FORCE_INLINE Square msb(Bitboard b) {
   unsigned long index;
   _BitScanReverse64(&index, b);
   return (Square) index;
 }
-#else
 
-FORCE_INLINE Square first_1(Bitboard b) { // Assembly code by Heinz van Saanen
+#  else
-  Bitboard dummy;
+
-  __asm__("bsfq %1, %0": "=r"(dummy): "rm"(b) );
+FORCE_INLINE Square lsb(Bitboard b) { // Assembly code by Heinz van Saanen
-  return (Square) dummy;
+  Bitboard index;
+  __asm__("bsfq %1, %0": "=r"(index): "rm"(b) );
+  return (Square) index;
 }
 
-FORCE_INLINE Square last_1(Bitboard b) {
+FORCE_INLINE Square msb(Bitboard b) {
-  Bitboard dummy;
+  Bitboard index;
-  __asm__("bsrq %1, %0": "=r"(dummy): "rm"(b) );
+  __asm__("bsrq %1, %0": "=r"(index): "rm"(b) );
-  return (Square) dummy;
+  return (Square) index;
 }
-#endif
 
-FORCE_INLINE Square pop_1st_bit(Bitboard* b) {
+#  endif
-  const Square s = first_1(*b);
+
-  *b &= ~(1ULL<<s);
+FORCE_INLINE Square pop_lsb(Bitboard* b) {
+  const Square s = lsb(*b);
+  *b &= ~(1ULL << s);
   return s;
 }
 
 #else // if !defined(USE_BSFQ)
 
-extern Square first_1(Bitboard b);
+extern Square msb(Bitboard b);
-extern Square last_1(Bitboard b);
+extern Square lsb(Bitboard b);
-extern Square pop_1st_bit(Bitboard* b);
+extern Square pop_lsb(Bitboard* b);
 
 #endif
 

src/bitcount.h

@@ -90,7 +90,7 @@ inline int popcount<CNT_HW_POPCNT>(Bitboard b) {
 #if !defined(USE_POPCNT)
 
   assert(false);
-  return int(b != 0); // Avoid 'b not used' warning
+  return b != 0; // Avoid 'b not used' warning
 
 #elif defined(_MSC_VER) && defined(__INTEL_COMPILER)
 

src/book.cpp

@@ -316,7 +316,7 @@ namespace {
     {
         // Piece offset is at 64 * polyPiece where polyPiece is defined as:
         // BP = 0, WP = 1, BN = 2, WN = 3, ... BK = 10, WK = 11
-        Square s = pop_1st_bit(&b);
+        Square s = pop_lsb(&b);
         Piece p = pos.piece_on(s);
         int polyPiece = 2 * (type_of(p) - 1) + (color_of(p) == WHITE);
         key ^= ZobPiece[64 * polyPiece + s];
@@ -325,7 +325,7 @@ namespace {
     b = pos.can_castle(ALL_CASTLES);
 
     while (b)
-        key ^= ZobCastle[pop_1st_bit(&b)];
+        key ^= ZobCastle[pop_lsb(&b)];
 
     if (pos.ep_square() != SQ_NONE)
         key ^= ZobEnPassant[file_of(pos.ep_square())];

src/evaluate.cpp

@@ -582,7 +582,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
             assert(b);
 
             if (!more_than_one(b) && (b & pos.pieces(Them)))
-                score += ThreatBonus[Piece][type_of(pos.piece_on(first_1(b)))];
+                score += ThreatBonus[Piece][type_of(pos.piece_on(lsb(b)))];
         }
 
         // Decrease score if we are attacked by an enemy pawn. Remaining part
@@ -870,7 +870,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
         return SCORE_ZERO;
 
     do {
-        Square s = pop_1st_bit(&b);
+        Square s = pop_lsb(&b);
 
         assert(pos.pawn_is_passed(Us, s));
 
@@ -976,7 +976,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
 
         while (b)
         {
-            s = pop_1st_bit(&b);
+            s = pop_lsb(&b);
             queeningSquare = relative_square(c, file_of(s) | RANK_8);
             queeningPath = forward_bb(c, s);
 
@@ -1017,7 +1017,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
 
     while (b)
     {
-        s = pop_1st_bit(&b);
+        s = pop_lsb(&b);
 
         // Compute plies from queening
         queeningSquare = relative_square(loserSide, file_of(s) | RANK_8);
@@ -1039,7 +1039,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
 
     while (b)
     {
-        s = pop_1st_bit(&b);
+        s = pop_lsb(&b);
         sacptg = blockersCount = 0;
         minKingDist = kingptg = 256;
 
@@ -1058,7 +1058,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
         // How many plies does it take to remove all the blocking pawns?
         while (blockers)
         {
-            blockSq = pop_1st_bit(&blockers);
+            blockSq = pop_lsb(&blockers);
             movesToGo = 256;
 
             // Check pawns that can give support to overcome obstacle, for instance
@@ -1069,7 +1069,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
 
                 while (b2) // This while-loop could be replaced with LSB/MSB (depending on color)
                 {
-                    d = square_distance(blockSq, pop_1st_bit(&b2)) - 2;
+                    d = square_distance(blockSq, pop_lsb(&b2)) - 2;
                     movesToGo = std::min(movesToGo, d);
                 }
             }
@@ -1079,7 +1079,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
 
             while (b2) // This while-loop could be replaced with LSB/MSB (depending on color)
             {
-                d = square_distance(blockSq, pop_1st_bit(&b2)) - 2;
+                d = square_distance(blockSq, pop_lsb(&b2)) - 2;
                 movesToGo = std::min(movesToGo, d);
             }
 

src/movegen.cpp

@@ -25,10 +25,10 @@
 
 /// Simple macro to wrap a very common while loop, no facny, no flexibility,
 /// hardcoded names 'mlist' and 'from'.
-#define SERIALIZE(b) while (b) (*mlist++).move = make_move(from, pop_1st_bit(&b))
+#define SERIALIZE(b) while (b) (*mlist++).move = make_move(from, pop_lsb(&b))
 
 /// Version used for pawns, where the 'from' square is given as a delta from the 'to' square
-#define SERIALIZE_PAWNS(b, d) while (b) { Square to = pop_1st_bit(&b); \
+#define SERIALIZE_PAWNS(b, d) while (b) { Square to = pop_lsb(&b); \
                                          (*mlist++).move = make_move(to - (d), to); }
 namespace {
 
@@ -87,7 +87,7 @@ namespace {
 
     while (b)
     {
-        Square to = pop_1st_bit(&b);
+        Square to = pop_lsb(&b);
 
         if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
             (*mlist++).move = make<PROMOTION>(to - Delta, to, QUEEN);
@@ -207,7 +207,7 @@ namespace {
             assert(b1);
 
             while (b1)
-                (*mlist++).move = make<ENPASSANT>(pop_1st_bit(&b1), pos.ep_square());
+                (*mlist++).move = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
         }
     }
 
@@ -343,7 +343,7 @@ MoveStack* generate<QUIET_CHECKS>(const Position& pos, MoveStack* mlist) {
 
   while (dc)
   {
-     Square from = pop_1st_bit(&dc);
+     Square from = pop_lsb(&dc);
      PieceType pt = type_of(pos.piece_on(from));
 
      if (pt == PAWN)
@@ -398,7 +398,7 @@ MoveStack* generate<EVASIONS>(const Position& pos, MoveStack* mlist) {
   do
   {
       checkersCnt++;
-      checksq = pop_1st_bit(&b);
+      checksq = pop_lsb(&b);
 
       assert(color_of(pos.piece_on(checksq)) == ~us);
 

src/notation.cpp

@@ -108,7 +108,7 @@ const string move_to_san(Position& pos, Move m) {
 
           while (attackers)
           {
-              Square sq = pop_1st_bit(&attackers);
+              Square sq = pop_lsb(&attackers);
 
               // Pinned pieces are not included in the possible sub-set
               if (!pos.pl_move_is_legal(make_move(sq, to), pos.pinned_pieces()))

src/pawns.cpp

@@ -240,12 +240,12 @@ Value PawnEntry::shelter_storm(const Position& pos, Square ksq) {
   {
       // Shelter penalty is higher for the pawn in front of the king
       b = ourPawns & FileBB[f];
-      rkUs = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
+      rkUs = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
       safety -= ShelterWeakness[f != kf][rkUs];
 
       // Storm danger is smaller if enemy pawn is blocked
       b  = theirPawns & FileBB[f];
-      rkThem = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
+      rkThem = b ? rank_of(Us == WHITE ? lsb(b) : ~msb(b)) : RANK_1;
       safety -= StormDanger[rkThem == rkUs + 1][rkThem];
   }
 

src/position.cpp

@@ -359,7 +359,7 @@ Bitboard Position::hidden_checkers() const {
 
   while (pinners)
   {
-      b = between_bb(ksq, pop_1st_bit(&pinners)) & pieces();
+      b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
 
       if (b && !more_than_one(b) && (b & pieces(sideToMove)))
           result |= b;
@@ -597,7 +597,7 @@ bool Position::is_pseudo_legal(const Move m) const {
       if (type_of(pc) != KING)
       {
           Bitboard b = checkers();
-          Square checksq = pop_1st_bit(&b);
+          Square checksq = pop_lsb(&b);
 
           if (b) // double check ? In this case a king move is required
               return false;
@@ -1323,7 +1323,7 @@ Key Position::compute_key() const {
 
   for (Bitboard b = pieces(); b; )
   {
-      Square s = pop_1st_bit(&b);
+      Square s = pop_lsb(&b);
       k ^= zobrist[color_of(piece_on(s))][type_of(piece_on(s))][s];
   }
 
@@ -1349,7 +1349,7 @@ Key Position::compute_pawn_key() const {
 
   for (Bitboard b = pieces(PAWN); b; )
   {
-      Square s = pop_1st_bit(&b);
+      Square s = pop_lsb(&b);
       k ^= zobrist[color_of(piece_on(s))][PAWN][s];
   }
 
@@ -1386,7 +1386,7 @@ Score Position::compute_psq_score() const {
 
   for (Bitboard b = pieces(); b; )
   {
-      Square s = pop_1st_bit(&b);
+      Square s = pop_lsb(&b);
       score += pieceSquareTable[piece_on(s)][s];
   }
 
@@ -1477,7 +1477,7 @@ void Position::init() {
       Bitboard b = cr;
       while (b)
       {
-          Key k = zobCastle[1ULL << pop_1st_bit(&b)];
+          Key k = zobCastle[1ULL << pop_lsb(&b)];
           zobCastle[cr] ^= k ? k : rk.rand<Key>();
       }
   }

src/search.cpp

@@ -1354,7 +1354,7 @@ split_point_start: // At split points actual search starts from here
     while (b)
     {
         // Note that here we generate illegal "double move"!
-        if (futilityBase + PieceValueEndgame[pos.piece_on(pop_1st_bit(&b))] >= beta)
+        if (futilityBase + PieceValueEndgame[pos.piece_on(pop_lsb(&b))] >= beta)
             return true;
     }
 

src/tt.cpp

@@ -44,7 +44,7 @@ TranspositionTable::~TranspositionTable() {
 
 void TranspositionTable::set_size(size_t mbSize) {
 
-  size_t newSize = 1ULL << last_1((mbSize << 20) / sizeof(TTCluster));
+  size_t newSize = 1ULL << msb((mbSize << 20) / sizeof(TTCluster));
 
   if (newSize == size)
       return;
@@ -60,7 +60,7 @@ void TranspositionTable::set_size(size_t mbSize) {
       exit(EXIT_FAILURE);
   }
 
-  clear(); // operator new is not guaranteed to initialize memory to zero
+  clear(); // Operator new is not guaranteed to initialize memory to zero
 }