X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fbitboard.cpp;h=de28e03a05c4ef345ab0d89db30d206046811637;hp=44e00da0a4cb25f4257a643e716da49c51783064;hb=bc54a44010e7a7fb55ee55afba65be029a9e423a;hpb=47959c56fd9abfbf07278b3efeb6f458fcb4830b

diff --git a/src/bitboard.cpp b/src/bitboard.cpp
index 44e00da0..de28e03a 100644
--- a/src/bitboard.cpp
+++ b/src/bitboard.cpp
@@ -212,8 +212,8 @@ void init_bitboards() {
                      {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
 
   for (Color c = WHITE; c <= BLACK; c++)
-      for (Square s = SQ_A1; s <= SQ_H8; s++)
-          for (PieceType pt = PAWN; pt <= KING; pt++)
+      for (PieceType pt = PAWN; pt <= KING; pt++)
+          for (Square s = SQ_A1; s <= SQ_H8; s++)
               for (int k = 0; steps[pt][k]; k++)
               {
                   Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
@@ -252,26 +252,7 @@ void init_bitboards() {
 
 namespace {
 
-  Bitboard submask(Bitboard mask, int key) {
-
-    Bitboard b, subMask = 0;
-    int bitProbe = 1;
-
-    // Extract an unique submask out of a mask according to the given key
-    while (mask)
-    {
-        b = mask & -mask;
-        mask ^= b;
-
-        if (key & bitProbe)
-            subMask |= b;
-
-        bitProbe <<= 1;
-    }
-    return subMask;
-  }
-
-  Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[], Bitboard excluded) {
+  Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[]) {
 
     Bitboard attacks = 0;
 
@@ -279,9 +260,7 @@ namespace {
     {
         Square s = sq + delta[i];
 
-        while (    square_is_ok(s)
-               &&  square_distance(s, s - delta[i]) == 1
-               && !bit_is_set(excluded, s))
+        while (square_is_ok(s) && square_distance(s, s - delta[i]) == 1)
         {
             set_bit(&attacks, s);
 
@@ -321,28 +300,28 @@ namespace {
     const int  MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
                                       { 1059, 3608,  605, 3234, 3326,   38, 2029, 3043 } };
     RKISS rk;
-    Bitboard occupancy[4096], reference[4096], excluded;
+    Bitboard occupancy[4096], reference[4096], edges, b;
     int key, maxKey, index, booster, offset = 0;
 
     for (Square s = SQ_A1; s <= SQ_H8; s++)
     {
-        excluded = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
+        edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
 
         attack[s] = &attTable[offset];
-        mask[s]   = sliding_attacks(s, EmptyBoardBB, delta, excluded);
+        mask[s]   = sliding_attacks(s, EmptyBoardBB, delta) & ~edges;
         shift[s]  = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(mask[s]);
 
-        maxKey = 1 << count_1s<CNT32_MAX15>(mask[s]);
+        // Use Carry-Rippler trick to enumerate all subsets of mask[s]
+        b = maxKey = 0;
+        do {
+            occupancy[maxKey] = b;
+            reference[maxKey++] = sliding_attacks(s, b, delta);
+            b = (b - mask[s]) & mask[s];
+        } while (b);
+
         offset += maxKey;
         booster = MagicBoosters[CpuIs64Bit][square_rank(s)];
 
-        // First compute occupancy and attacks for square 's'
-        for (key = 0; key < maxKey; key++)
-        {
-            occupancy[key] = submask(mask[s], key);
-            reference[key] = sliding_attacks(s, occupancy[key], delta, EmptyBoardBB);
-        }
-
         // Then find a possible magic and the corresponding attacks
         do {
             magic[s] = pick_magic(mask[s], rk, booster);