chessy/src/BitBoard.h

#ifndef CHESSY_BITBOARD_H
#define CHESSY_BITBOARD_H

#include "BitOperations.h"

#include <cinttypes>
#include <type_traits>
#include <string>


namespace chessy
{
    enum PieceType : char;

    struct Index;

    struct Move;

    struct Bitboard;

    using Side = int;

    const Side WHITE_SIDE = 0;
    const Side BLACK_SIDE = 1;

    inline constexpr Side otherSide(Side side)
    {
        return !side;
    }
}


enum chessy::PieceType : char
{
    EMPTY = -1,
    PAWN = 0,
    KNIGHT = 1,
    BISHOP = 2,
    ROOK = 3,
    QUEEN = 4,
    KING = 5,
};


/*!
 * data structure to index one field on a chess board
 */
struct chessy::Index
{
    int8_t index;

    Index(void) = default;
    inline constexpr Index(int8_t ind) : index{ ind } {}
    inline Index(const std::string& name) :
        Index{ name[1] - '1', name[0] - 'a' } {}
    inline constexpr Index(int row, int column) :
        index{int8_t(((row & 0x7) << 3) + (column & 0x7))} {}


    inline operator int8_t  (void) const    { return index; }

    inline int getColumn    (void) const    { return index & 0x7; }
    inline int getRow       (void) const    { return (index >> 3) & 0x7; }

    inline std::string getName(void) const
    {
        return { char('a' + getColumn()), char(getRow() + '1') };
    }
};


/*!
 * data structure that holds a simple move
 */
struct chessy::Move
{
    Index origin;
    Index destination;

    //! If the move is a promotion move, this field stores
    //! the type of the resulting piece.
    //! If this field is equal to <code>PieceType::PAWN</code>,
    //! it is indicated, that no promotion happened.
    PieceType promotion;

    bool isCastling;


    Move            (void)          = default;
    Move            (const Move&)   = default;
    Move            (Move&&)        = default;
    ~Move           (void)          = default;
    Move& operator= (const Move&)   = default;
    Move& operator= (Move&&)        = default;

    inline Move(const std::string& move) :
        promotion{ PieceType::PAWN }, isCastling{ false }
    {
        if (move.length() < 4)
            return;
        origin = Index { move.substr(0, 2) };
        destination = Index { move.substr(2, 2) };
        if (move.length() > 4) {
            switch (move[4]) {
            case 'n': promotion = PieceType::KNIGHT; break;
            case 'b': promotion = PieceType::BISHOP; break;
            case 'r': promotion = PieceType::ROOK; break;
            case 'q': promotion = PieceType::QUEEN; break;
            }
        }
    }

    inline Move(Index origin, Index destination) :
        origin{ origin }, destination{ destination },
        promotion{ PieceType::PAWN }, isCastling{ false } {}

    inline Move(Index origin, Index destination, PieceType promotion) :
        origin{ origin }, destination{ destination }, promotion{ promotion },
        isCastling{ false } {}

    inline Move(Index origin, Index destination, bool isCastling) :
        origin{ origin }, destination{ destination },
        promotion{ PieceType::PAWN }, isCastling{ isCastling } {}

    inline std::string asString(void) const
    {
        return origin.getName() + destination.getName() +
            (promotion == PieceType::KNIGHT ? "n" : "") +
            (promotion == PieceType::BISHOP ? "b" : "") +
            (promotion == PieceType::ROOK ? "r" : "") +
            (promotion == PieceType::QUEEN ? "q" : "");
    }
};


struct chessy::Bitboard
{
    U64 bits;

    Bitboard            (void)                  = default;
    Bitboard            (const Bitboard&)       = default;
    Bitboard            (Bitboard&&)            = default;
    ~Bitboard           (void)                  = default;
    Bitboard& operator= (const Bitboard&)       = default;
    Bitboard& operator= (Bitboard&&)            = default;

    inline constexpr Bitboard(U64 bits) : bits{ bits } {}
    inline static Bitboard fromIndex(Index i) { return U64(1) << i; }

    inline void     setBit      (Index i)     { bits |= U64(1) << i.index; }
    inline void     unsetBit    (Index i)     { bits |= ~(U64(1) << i.index); }
    inline void     toggleBit   (Index i)     { bits ^= U64(1) << i.index; }

    inline void     setBit      (int row, int column)
        { setBit(row * 8 + column); }
    inline void     unsetBit    (int row, int column)
        { unsetBit(row * 8 + column); }

    static const    U64 hColumn             = 0x0101010101010101ULL;
    static const    U64 aColumn             = 0x8080808080808080ULL;
    inline void     moveNorth   (int dist)  { bits <<= (8 * dist); }
    inline Bitboard north       (int dist)  { return bits << (8 * dist); }
    inline void     moveSouth   (int dist)  { bits >>= (8 * dist); }
    inline Bitboard south       (int dist)  { return bits >> (8 * dist); }
    inline void     moveNorthOne(void)      { bits <<= 8; }
    inline Bitboard northOne    (void)      { return bits << 8; }
    inline void     moveSouthOne(void)      { bits >>= 8; }
    inline Bitboard southOne    (void)      { return bits >> 8; }
    inline void     moveEastOne (void)      { bits = (bits & ~hColumn) >> 1; }
    inline Bitboard eastOne     (void)      { return (bits & ~hColumn) >> 1; }
    inline void     moveWestOne (void)      { bits = (bits & ~aColumn) << 1; }
    inline Bitboard westOne     (void)      { return (bits & ~aColumn) << 1; }
    inline void     moveNWOne   (void)      { bits = (bits << 7) & ~aColumn; }
    inline Bitboard nwOne       (void)      { return (bits << 7) & ~aColumn; }
    inline void     moveNEOne   (void)      { bits = (bits << 9) & ~hColumn; }
    inline Bitboard neOne       (void)      { return (bits << 9) & ~hColumn; }
    inline void     moveSWOne   (void)      { bits = (bits >> 9) & ~aColumn; }
    inline Bitboard swOne       (void)      { return (bits >> 9) & ~aColumn; }
    inline void     moveSEOne   (void)      { bits = (bits >> 7) & ~hColumn; }
    inline Bitboard seOne       (void)      { return (bits >> 7) & ~hColumn; }

    inline static Bitboard getColumn(int index)
    {
        return hColumn << index;
    }
    
    inline static Bitboard getRow(int index)
    {
        return 0xFFULL << (index * 8);
    }

    template<Side side>
    inline void     pushOne(void)
    {
        if (side == WHITE_SIDE)
            moveNorthOne();
        else
            moveSouthOne();
    }

    inline void     operator &= (const Bitboard& b)         { bits &= b.bits; }
    inline void     operator |= (const Bitboard& b)         { bits |= b.bits; }
    inline void     operator ^= (const Bitboard& b)         { bits ^= b.bits; }

    inline Bitboard operator &  (const Bitboard& b) const   { return bits & b.bits; }
    inline Bitboard operator |  (const Bitboard& b) const   { return bits | b.bits; }
    inline Bitboard operator ^  (const Bitboard& b) const   { return bits ^ b.bits; }
    inline Bitboard operator ~  (void) const                { return ~bits; }
    inline bool     operator == (const Bitboard& b) const   { return bits == b.bits; }
    inline bool     operator != (const Bitboard& b) const   { return bits != b.bits; }
    inline          operator U64(void) const                { return bits; }
    inline explicit operator bool(void) const               { return bits != 0; }

    inline void applyMove(Move move)
    {
        bits &= ~fromIndex(move.origin);
        bits |= fromIndex(move.destination);
    }

    inline Bitboard mirror(void) const                      { return byteswap(bits); }
    inline Index    getLeastSignificantBit (void) const     { return trailingZeroes(bits); }
    inline int      popcount    (void) const                { return chessy::popcount(bits); }

    static const uint64_t aFile = 0x8080808080808080ULL;
    static const uint64_t hFile = 0x0101010101010101ULL;
};


static_assert(std::is_pod<chessy::Bitboard>::value,
    "chessy::Bitboard should be a POD structure.");
static_assert(std::is_pod<chessy::Index>::value,
    "chessy::Index should be a POD structure.");
static_assert(sizeof(chessy::Bitboard) == sizeof(uint64_t),
    "chessy::Bitboard should be 64 bits in size.");


#endif // CHESSY_BITBOARD_H