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Implementing pin detection (#71)
* added a new bitboard constructor from a square * implemented and tested pins functions * renamed internal lib to Bitbishop * updated clang tidy rules to support 'us' color * fixed linting
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12 files changed

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-7
lines changed

‎.clang-tidy‎

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@@ -9,8 +9,8 @@ WarningsAsErrors: "*"
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CheckOptions:
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- key: readability-identifier-length.IgnoredVariableNames
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value: "^(sq|to|from|bb|A[1-8]|B[1-8]|C[1-8]|D[1-8]|E[1-8]|F[1-8]|G[1-8]|H[1-8])$"
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value: "^(sq|to|from|bb|us|A[1-8]|B[1-8]|C[1-8]|D[1-8]|E[1-8]|F[1-8]|G[1-8]|H[1-8])$"
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- key: readability-identifier-length.IgnoredParameterNames
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value: "^(sq|to|from|bb)$"
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value: "^(sq|to|from|bb|us)$"
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- key: readability-identifier-length.IgnoredLoopCounterNames
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value: "^(r|f)$"

‎include/bitbishop/bitboard.hpp‎

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@@ -49,6 +49,9 @@ class Bitboard {
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/** @brief Constructs a bitboard from another bitboard by copy. */
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constexpr Bitboard(const Bitboard& bitboard) : m_bb(bitboard.value()) {}
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/** @brief Constructs a bitboard with the given square being the only bit set to one. */
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constexpr Bitboard(Square square) : m_bb(0ULL) { set(square); }
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/** @brief Returns the raw 64-bit value of the bitboard. */
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[[nodiscard]] constexpr uint64_t value() const { return m_bb; }
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‎include/bitbishop/movegen/pins.hpp‎

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@@ -0,0 +1,131 @@
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#include <bitbishop/bitboard.hpp>
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#include <bitbishop/board.hpp>
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#include <bitbishop/lookups/between_squares.hpp>
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#include <bitbishop/lookups/bishop_rays.hpp>
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#include <bitbishop/lookups/rook_rays.hpp>
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#include <bitbishop/square.hpp>
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/**
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* @brief Enumeration of sliding ray types used for pin detection.
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*
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* Distinguishes between rook-like and bishop-like rays,
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* determining which enemy sliders can produce a pin.
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*/
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enum class RayType : std::uint8_t {
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ROOK, ///< Orthogonal rays (rook / queen)
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BISHOP ///< Diagonal rays (bishop / queen)
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};
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/**
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* @brief Enumeration of ray directions from the king square.
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*
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* Used to determine ray orientation and correct blocker ordering
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* (LSB vs MSB) when scanning occupied squares.
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*/
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enum class RayDir : std::uint8_t {
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N,
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S,
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E,
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W, ///< Orthogonal directions
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NE,
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NW,
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SE,
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SW ///< Diagonal directions
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};
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/**
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* @brief Describes a single ray used for pin detection.
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*
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* A PinRay represents one directional ray starting from the king square,
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* along with the information required to:
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* - determine blocker ordering
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* - validate enemy sliding pieces that can create pins
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*/
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struct PinRay {
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Bitboard ray; ///< Precomputed ray bitboard from the king square
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RayType type; ///< Type of sliding piece relevant for this ray
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RayDir dir; ///< Direction of the ray
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/**
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* @brief Returns the first blocker along this ray.
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*
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* The function selects either the least-significant or most-significant
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* bit depending on the ray direction.
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*
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* @param bb Bitboard of occupied squares along the ray
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* @return Square of the closest blocker to the king
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*/
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[[nodiscard]] Square first_blocker(const Bitboard& bb) const {
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switch (dir) {
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case RayDir::N:
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case RayDir::NE:
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case RayDir::E:
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case RayDir::NW:
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return bb.lsb().value();
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default:
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return bb.msb().value();
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}
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}
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/**
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* @brief Checks whether a piece matches the required enemy slider for this ray.
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*
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* For rook rays, accepts enemy rooks or queens.
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* For bishop rays, accepts enemy bishops or queens.
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*
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* @param piece Bitboard with a single enemy piece
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* @param board Current board state
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* @param them Enemy color
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* @return true if the piece can create a pin along this ray
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*/
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[[nodiscard]] bool matches_slider(const Bitboard& piece, const Board& board, Color them) const {
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return (type == RayType::BISHOP) ? (piece & (board.bishops(them) | board.queens(them)))
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: (piece & (board.rooks(them) | board.queens(them)));
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}
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};
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/**
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* @brief Result structure for pin computation.
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*
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* Contains:
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* - a bitboard of all pinned friendly pieces
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* - a per-square pin ray mask restricting legal movement
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*/
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struct PinResult {
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Bitboard pinned = Bitboard::Zeros();
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std::array<Bitboard, Const::BOARD_SIZE> pin_ray{};
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};
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/**
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* @brief Scans a single ray from the king to detect a possible pin.
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*
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* The function detects the classical pin pattern:
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* king → friendly piece → enemy sliding piece
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*
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* If such a configuration is found:
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* - the friendly piece is marked as pinned
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* - its legal movement is restricted to the pin ray
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*
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* @param king_sq Square of the friendly king
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* @param ray_info Ray descriptor (direction, type, bitboard)
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* @param board Current board position
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* @param us Friendly color
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* @param result Accumulated pin result (modified in place)
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*/
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void scan_pin_ray(Square king_sq, const PinRay& ray_info, const Board& board, Color us, PinResult& result);
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/**
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* @brief Computes all pinned pieces for the given side.
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*
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* Pins are detected by scanning all rook and bishop rays
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* originating from the king square.
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*
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* A piece is considered pinned if moving it would expose
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* the king to a sliding attack.
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*
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* @param king_sq Square of the friendly king
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* @param board Current board position
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* @param us Friendly color
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* @return PinResult containing pinned pieces and their pin rays
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*/
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PinResult compute_pins(Square king_sq, const Board& board, Color us);

‎main/CMakeLists.txt‎

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@@ -1,10 +1,10 @@
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message(STATUS "> Found main directory")
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add_executable(SandBox sandbox.cpp)
4-
target_link_libraries(SandBox PRIVATE ChessEngineLib spdlog::spdlog)
4+
target_link_libraries(SandBox PRIVATE Bitbishop spdlog::spdlog)
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66
add_executable(UCIChessEngine uci_loop.cpp)
7-
target_link_libraries(UCIChessEngine PRIVATE ChessEngineLib spdlog::spdlog)
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target_link_libraries(UCIChessEngine PRIVATE Bitbishop spdlog::spdlog)
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set_property(
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TARGET

‎src/bitbishop/CMakeLists.txt‎

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@@ -4,7 +4,7 @@ message(STATUS "> Found src/bitbishop directory")
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option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
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# Define the library target name and source folder
7-
set(target_name ChessEngineLib)
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set(target_name Bitbishop)
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set(target_folder_name bitbishop)
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# Search and list all .cpp files in the source folder
@@ -54,7 +54,7 @@ target_include_directories(${target_name}
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)
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# Define the folder in the IDE where the target will appear
57-
set_property(TARGET ${target_name} PROPERTY FOLDER ChessEngineLib)
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set_property(TARGET ${target_name} PROPERTY FOLDER Bitbishop)
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# Library packaging section
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‎src/bitbishop/movegen/pins.cpp‎

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@@ -0,0 +1,56 @@
1+
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#include <bitbishop/movegen/pins.hpp>
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void scan_pin_ray(Square king_sq, const PinRay& ray_info, const Board& board, Color us, PinResult& result) {
5+
const Bitboard occupied = board.occupied();
6+
const Bitboard own = board.friendly(us);
7+
const Color them = ColorUtil::opposite(us);
8+
9+
Bitboard blockers = ray_info.ray & occupied;
10+
if (!blockers) {
11+
return;
12+
}
13+
14+
Square first_blocker_sq = ray_info.first_blocker(blockers);
15+
Bitboard first_blocker_bb(first_blocker_sq);
16+
if (!(first_blocker_bb & own)) {
17+
return;
18+
}
19+
20+
Bitboard beyond = ray_info.ray & ~(Lookups::BETWEEN[king_sq.value()][first_blocker_sq.value()] | first_blocker_bb);
21+
Bitboard second_blockers_bb = beyond & occupied;
22+
if (!second_blockers_bb) {
23+
return;
24+
}
25+
26+
Square second_blocker_sq = ray_info.first_blocker(second_blockers_bb);
27+
Bitboard second_blocker_bb(second_blocker_sq);
28+
if (!ray_info.matches_slider(second_blocker_bb, board, them)) {
29+
return;
30+
}
31+
32+
result.pinned |= first_blocker_bb;
33+
result.pin_ray[first_blocker_sq.value()] =
34+
Lookups::BETWEEN[king_sq.value()][second_blocker_sq.value()] | second_blocker_bb;
35+
}
36+
37+
PinResult compute_pins(Square king_sq, const Board& board, Color us) {
38+
PinResult result;
39+
40+
const std::array<PinRay, 8> ray_infos = {{
41+
PinRay{.ray = Lookups::ROOK_NORTH_RAYS[king_sq.value()], .type = RayType::ROOK, .dir = RayDir::N},
42+
PinRay{.ray = Lookups::ROOK_SOUTH_RAYS[king_sq.value()], .type = RayType::ROOK, .dir = RayDir::S},
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PinRay{.ray = Lookups::ROOK_EAST_RAYS[king_sq.value()], .type = RayType::ROOK, .dir = RayDir::E},
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PinRay{.ray = Lookups::ROOK_WEST_RAYS[king_sq.value()], .type = RayType::ROOK, .dir = RayDir::W},
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PinRay{.ray = Lookups::BISHOP_NORTHEAST_RAYS[king_sq.value()], .type = RayType::BISHOP, .dir = RayDir::NE},
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PinRay{.ray = Lookups::BISHOP_NORTHWEST_RAYS[king_sq.value()], .type = RayType::BISHOP, .dir = RayDir::NW},
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PinRay{.ray = Lookups::BISHOP_SOUTHEAST_RAYS[king_sq.value()], .type = RayType::BISHOP, .dir = RayDir::SE},
48+
PinRay{.ray = Lookups::BISHOP_SOUTHWEST_RAYS[king_sq.value()], .type = RayType::BISHOP, .dir = RayDir::SW},
49+
}};
50+
51+
for (const auto& ray_info : ray_infos) {
52+
scan_pin_ray(king_sq, ray_info, board, us, result);
53+
}
54+
55+
return result;
56+
}

‎tests/CMakeLists.txt‎

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Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ foreach(TEST_FILE ${TESTS_SOURCES})
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get_filename_component(TEST_NAME ${TEST_FILE} NAME_WE)
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add_executable(${TEST_NAME} ${TEST_FILE} ${TESTS_HEADERS})
1010
add_test(NAME ${TEST_NAME} COMMAND ${TEST_NAME})
11-
target_link_libraries(${TEST_NAME} PRIVATE ChessEngineLib GTest::gtest GTest::gtest_main)
11+
target_link_libraries(${TEST_NAME} PRIVATE Bitbishop GTest::gtest GTest::gtest_main)
1212
target_include_directories(${TEST_NAME} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
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set_property(TARGET ${TEST_NAME} PROPERTY FOLDER Tests)
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endforeach(TEST_FILE)

‎tests/bitbishop/bitboard/test_bb_constructors.cpp‎

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Original file line numberDiff line numberDiff line change
@@ -93,3 +93,15 @@ TEST(BitboardTest, OnesStaticConstructor) {
9393
static_assert(bb.value() == (~0ULL), "Bitboard::Ones() static constructor must be constexpr");
9494
EXPECT_EQ(bb.value(), (~0ULL));
9595
}
96+
97+
/**
98+
* @test Bitboard(Square) constructor.
99+
* @brief Verifies that the constructor can be evaluated at compile time.
100+
*/
101+
TEST(BitboardConstructorsTest, SquareConstructorIsConstexpr) {
102+
constexpr Bitboard bb = Bitboard(Squares::A4);
103+
104+
static_assert(bb.test(Squares::A4) == true, "Bitboard(Square) must be constexpr");
105+
EXPECT_TRUE(bb.test(Squares::A4));
106+
EXPECT_EQ(bb.count(), 1);
107+
}

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