removing hard coded knight moves

1 files changed, 31 insertions, 24 deletions

diff --git a/src/moves.cpp b/src/moves.cpp
index a130055..52c8d2f 100644
--- a/src/moves.cpp
+++ b/src/moves.cpp
@@ -1,5 +1,6 @@
 #include <array>
 #include <cassert>
+#include <cstddef>
 #include <cstdint>
 #include <cstdlib>
 #include <iostream>
@@ -9,29 +10,31 @@
 #include "board/board.hpp"
 #include "moves.hpp"
 
-constexpr std::array<uint64_t, 64> KNIGHT_ATTACKS = {
-    0x0000000000020400ULL, 0x0000000000050800ULL, 0x00000000000A1100ULL,
-    0x0000000000142200ULL, 0x0000000000284400ULL, 0x0000000000508800ULL,
-    0x0000000000A01000ULL, 0x0000000000402000ULL, 0x0000000002040004ULL,
-    0x0000000005080008ULL, 0x000000000A110011ULL, 0x0000000014220022ULL,
-    0x0000000028440044ULL, 0x0000000050880088ULL, 0x00000000A0100010ULL,
-    0x0000000040200020ULL, 0x0000000204000402ULL, 0x0000000508000805ULL,
-    0x0000000A1100110AULL, 0x0000001422002214ULL, 0x0000002844004428ULL,
-    0x0000005088008850ULL, 0x000000A0100010A0ULL, 0x0000004020002040ULL,
-    0x0000020400040200ULL, 0x0000050800080500ULL, 0x00000A1100110A00ULL,
-    0x0000142200221400ULL, 0x0000284400442800ULL, 0x0000508800885000ULL,
-    0x0000A0100010A000ULL, 0x0000402000204000ULL, 0x0002040004020000ULL,
-    0x0005080008050000ULL, 0x000A1100110A0000ULL, 0x0014220022140000ULL,
-    0x0028440044280000ULL, 0x0050880088500000ULL, 0x00A0100010A00000ULL,
-    0x0040200020400000ULL, 0x0204000402000000ULL, 0x0508000805000000ULL,
-    0x0A1100110A000000ULL, 0x1422002214000000ULL, 0x2844004428000000ULL,
-    0x5088008850000000ULL, 0xA0100010A0000000ULL, 0x4020002040000000ULL,
-    0x0400040200000000ULL, 0x0800080500000000ULL, 0x1100110A00000000ULL,
-    0x2200221400000000ULL, 0x4400442800000000ULL, 0x8800885000000000ULL,
-    0x100010A000000000ULL, 0x2000204000000000ULL, 0x0004020000000000ULL,
-    0x0008050000000000ULL, 0x00110A0000000000ULL, 0x0022140000000000ULL,
-    0x0044280000000000ULL, 0x0088500000000000ULL, 0x0010A00000000000ULL,
-    0x0020400000000000ULL};
+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);
+      }
+    }
+    attacks[static_cast<size_t>(sq)] = bb;
+  }
+  return attacks;
+}
+
+constexpr std::array<std::uint64_t, 64> KNIGHT_ATTACKS = computeKnightAttacks();
 
 static void GenerateKnightMoves(Game *b, std::vector<Move> &moves,
                                 bool GenerateQuietMoves) {
@@ -44,17 +47,21 @@ static void GenerateKnightMoves(Game *b, std::vector<Move> &moves,
       int next = __builtin_ctzll(knight_attacks);
       knight_attacks &= knight_attacks - 1;
 
+      // maybe remove this line of code
       if (next >= 64 || next < 0) {
         continue;
       }
+
+      // maybe also remove this line of code
       const int fileDelta = std::abs((next % 8) - (from % 8));
       if (fileDelta != 1 && fileDelta != 2) {
         continue;
       };
+
       bool hasFriendlyPiece =
           b->turn ? (b->WhitePieceBitboard & (1ULL << next)) > 0
                   : (b->BlackPieceBitboard & (1ULL << next)) > 0;
-      
+
       bool isCaptuare = (b->PieceBitboard & (1ULL << next)) > 0;
       if (hasFriendlyPiece) {
         continue;