improving knight move gen code

1 files changed, 16 insertions, 15 deletions

diff --git a/src/moves.cpp b/src/moves.cpp
index 3cdeafa..a236536 100644
--- a/src/moves.cpp
+++ b/src/moves.cpp
@@ -13,23 +13,23 @@
 constexpr std::array<std::uint64_t, 64> computeKnightAttacks() {
   std::array<std::uint64_t, 64> attacks{};
 
-  for (int sq = 0; sq < 64; ++sq) {
-    const int f = sq % 8; // file (0=a, 7=h)
-    const int r = sq / 8; // rank (0=1, 7=8)
-    std::uint64_t bb = 0;
-
-    // {df, dr} for all 8 knight leaps
-    const int leaps[8][2] = {{1, 2},   {2, 1},   {2, -1}, {1, -2},
-                             {-1, -2}, {-2, -1}, {-2, 1}, {-1, 2}};
-
-    for (int i = 0; i < 8; ++i) {
-      const int nf = f + leaps[i][0];
-      const int nr = r + leaps[i][1];
-      if (nf >= 0 && nf < 8 && nr >= 0 && nr < 8) {
-        bb |= 1ULL << (nr * 8 + nf);
+  constexpr std::array<int, 8> knight_moves{-10, 6, 15, 17, 10, -6, -15, -17};
+
+  for (int i = 0; i < 64; i++) {
+    uint64_t bb = 0;
+    for (int offset : knight_moves) {
+      int next = i + offset;
+      if (next >= 64 || next < 0) {
+        continue;
       }
+      const int fileDelta = (next % 8) - (i % 8);
+      if (fileDelta != 1 && fileDelta != 2 && fileDelta != -1 &&
+          fileDelta != -2) {
+        continue;
+      };
+      bb |= 1ULL << next;
     }
-    attacks[static_cast<size_t>(sq)] = bb;
+    attacks[static_cast<size_t>(i)] = bb;
   }
   return attacks;
 }
@@ -38,6 +38,7 @@ constexpr std::array<std::uint64_t, 64> KNIGHT_ATTACKS = computeKnightAttacks();
 
 static void GenerateKnightMoves(Game *b, std::vector<Move> &moves,
                                 bool GenerateQuietMoves) {
+                                
   uint64_t knights = b->PieceBitboards[b->turn][KNIGHT];
   while (knights != 0) {
     int from = __builtin_ctzll(knights);