implemented legal knights moves generation

Author: Hardcode3

include/bitbishop/movegen/knight_moves.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <bitbishop/board.hpp>
+#include <bitbishop/color.hpp>
+#include <bitbishop/lookups/knight_attacks.hpp>
+#include <bitbishop/move.hpp>
+#include <bitbishop/movegen/pins.hpp>
+#include <utility>
+#include <vector>
+
+void generate_knight_legal_moves(std::vector<Move>& moves, const Board& board, Color us, const Bitboard& check_mask,
+                                 const PinResult& pins) {
+  const Bitboard own = board.friendly(us);
+  const Bitboard enemy = board.enemy(us);
+  Bitboard knights = board.knights(us);
+  knights &= ~pins.pinned;
+
+  // warning: this loop is destructive on Bitboard knights
+  while (auto from_opt = knights.pop_lsb()) {
+    Square from = from_opt.value();
+
+    Bitboard candidates = Lookups::KNIGHT_ATTACKS[from.value()];
+    candidates &= ~own;
+    candidates &= check_mask;
+
+    for (Square to : candidates) {
+      const bool is_capture = enemy.test(to);
+      moves.emplace_back(from, to, std::nullopt, is_capture, false, false);
+    }
+  }
+}