More readable init of MS1BTable[]

[stockfish] / src / bitboard.cpp

diff --git a/src/bitboard.cpp b/src/bitboard.cpp
index 84405411555430c30eb091f5a6243d611fb1a65a..fd3db6715b6e15278a5c8d382d37798132adc37b 100644 (file)
--- a/src/bitboard.cpp
+++ b/src/bitboard.cpp
@@ -80,8 +80,8 @@ namespace {
   }
 }
 
-/// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
-/// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
+/// lsb()/msb() finds the least/most significant bit in a non-zero bitboard.
+/// pop_lsb() finds and clears the least significant bit in a non-zero bitboard.
 
 #ifndef USE_BSFQ
 
@@ -151,15 +151,11 @@ const std::string Bitboards::pretty(Bitboard b) {
 
 void Bitboards::init() {
 
-  for (int k = 0, i = 0; i < 8; ++i)
-      while (k < (2 << i))
-          MS1BTable[k++] = i;
-
-  for (int i = 0; i < 64; ++i)
-      BSFTable[bsf_index(1ULL << i)] = Square(i);
-
   for (Square s = SQ_A1; s <= SQ_H8; ++s)
-      SquareBB[s] = 1ULL << s;
+      BSFTable[bsf_index(SquareBB[s] = 1ULL << s)] = s;
+
+  for (Bitboard b = 1; b < 256; ++b)
+      MS1BTable[b] = more_than_one(b) ? MS1BTable[b - 1] : lsb(b);
 
   FileBB[FILE_A] = FileABB;
   RankBB[RANK_1] = Rank1BB;
@@ -198,9 +194,9 @@ void Bitboards::init() {
   for (Color c = WHITE; c <= BLACK; ++c)
       for (PieceType pt = PAWN; pt <= KING; ++pt)
           for (Square s = SQ_A1; s <= SQ_H8; ++s)
-              for (int k = 0; steps[pt][k]; ++k)
+              for (int i = 0; steps[pt][i]; ++i)
               {
-                  Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
+                  Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
 
                   if (is_ok(to) && square_distance(s, to) < 3)
                       StepAttacksBB[make_piece(c, pt)][s] |= to;
@@ -256,7 +252,7 @@ namespace {
   Bitboard pick_random(RKISS& rk, int booster) {
 
     // Values s1 and s2 are used to rotate the candidate magic of a
-    // quantity known to be the optimal to quickly find the magics.
+    // quantity known to be optimal to quickly find the magics.
     int s1 = booster & 63, s2 = (booster >> 6) & 63;
 
     Bitboard m = rk.rand<Bitboard>();