implemented bishop legal moves

cpp/src/pieces/bishop.cpp

@@ -0,0 +1,23 @@
+#include "../board.hpp"
+#include "../coords.hpp"
+#include "../move.hpp"
+#include "piece.hpp"
+
+#include <vector>
+
+std::vector<Move> bishop_moves(const Board& b, const Coords xy) {
+    std::vector<Move> ret;
+    auto ne = look_direction(b, xy, 1, 1);
+    ret.insert(ret.end(), ne.begin(), ne.end());
+
+    auto se = look_direction(b, xy, 1, -1);
+    ret.insert(ret.end(), se.begin(), se.end());
+
+    auto sw = look_direction(b, xy, -1, -1);
+    ret.insert(ret.end(), sw.begin(), sw.end());
+
+    auto nw = look_direction(b, xy, -1, 1);
+    ret.insert(ret.end(), nw.begin(), nw.end());
+
+    return ret;
+}

cpp/src/pieces/piece.cpp

@@ -36,3 +36,37 @@ std::vector<Move> legal_moves(
 
     return {};
 }
+
+std::optional<Move>
+move_for_position(const Board& board, const Coords source, const Coords dest) {
+    if (dest.is_within_bounds())
+        return {};
+
+    int8_t piece = board.squares[dest.to_index()];
+    if (piece == Piece::None)
+        return Move{source.to_index(), dest.to_index()};
+
+    int8_t source_colour = board.squares[source.to_index()] & 0b11000;
+    int8_t dest_colour = piece & 0b11000;
+    if (source_colour != dest_colour)
+        return Move{source.to_index(), dest.to_index(), true};
+    return {};
+}
+
+std::vector<Move>
+look_direction(const Board& board, const Coords xy, int mult_dx, int mult_dy) {
+    std::vector<Move> ret;
+    for (int d = 0; d < 8; d++) {
+        int dx = mult_dx * d;
+        int dy = mult_dy * d;
+
+        std::optional<Move> move =
+            move_for_position(board, xy, Coords{xy.x + dx, xy.y + dy});
+        if (move.has_value()) {
+            ret.push_back(move.value());
+            if (move.value().is_capturing)
+                break;
+        }
+    }
+    return ret;
+}

cpp/src/pieces/piece.hpp

@@ -3,6 +3,7 @@
 #include "../move.hpp"
 
 #include <cstdint>
+#include <optional>
 #include <vector>
 
 enum Piece : int8_t {
@@ -25,6 +26,8 @@ struct Coords;
 
 std::vector<Move> legal_moves(int8_t, const Board&, const Coords, bool);
 std::vector<Move> keep_only_blocking(const std::vector<Move>, const Board&);
+std::optional<Move> move_for_position(const Board&, const Coords, const Coords);
+std::vector<Move> look_direction(const Board&, const Coords, int, int);
 
 std::vector<Move> pawn_moves(const Board&, const Coords);
 std::vector<Move> rook_moves(const Board&, const Coords);