pleco_engine 0.1.6

//! A Table to store information concerning the structure of pawns. Used to evaluate
//! both the structure of the pawns, as well as king safety values.
//!
//! An entry is retrieved from the `pawn_key` field of a `Board`. A key is not garunteed to be
//! unique to a pawn structure, but it's very likely that there will be no collisions.

use std::mem::transmute;

use pleco::{Player, File, SQ, BitBoard, Board, PieceType, Rank, Piece};
use pleco::core::masks::{PLAYER_CNT,RANK_CNT};
use pleco::core::score::*;
use pleco::core::mono_traits::*;
use pleco::board::castle_rights::Castling;
use pleco::core::CastleType;
use pleco::helper::prelude::*;
use pleco::tools::{PreFetchable,prefetch_write};

use super::{TableBase,TableBaseConst};



// isolated pawn penalty
const ISOLATED: Score = Score(13, 18);

// backwards pawn penalty
const BACKWARDS: Score = Score(24, 12);

// doubled pawn penalty
const DOUBLED: Score = Score(18, 28);

// Lever bonus by rank
const LEVER: [Score; RANK_CNT] = [
    Score(0,0),
    Score(0,0),
    Score(0,0),
    Score(0,0),
    Score(17,16),
    Score(33,32),
    Score(0,0),
    Score(0,0),
];

const MAX_SAFETY_BONUS: Value = 258;


// Weakness of our pawn shelter in front of the king by [isKingFile][distance from edge][rank].
// RANK_1 = 0 is used for files where we have no pawns or our pawn is behind our king.
const SHELTER_WEAKNESS: [[[Value; RANK_CNT]; 4]; 2] = [
    [[  0,  97, 17,  9, 44,  84,  87,  99 ], // Not On King file
     [  0, 106,  6, 33, 86,  87, 104, 112 ],
     [  0, 101,  2, 65, 98,  58,  89, 115 ],
     [  0,  73,  7, 54, 73,  84,  83, 111 ] ],
    [[  0, 104, 20,  6, 27,  86,  93,  82 ], // On King file
     [  0, 123,  9, 34, 96, 112,  88,  75 ],
     [  0, 120, 25, 65, 91,  66,  78, 117 ],
     [  0,  81,  2, 47, 63,  94,  93, 104 ] ]
];

// Danger of enemy pawns moving toward our king by [type][distance from edge][rank].
// For the unopposed and unblocked cases, RANK_1 = 0 is used when opponent has
// no pawn on the given file, or their pawn is behind our king.
const STORM_DANGER: [[[Value; RANK_CNT]; 4]; 4] = [
    [ [  0, -290, -274, 57, 41, 0, 0, 0 ],  // BlockedByKing
      [  0,   60,  144, 39, 13, 0, 0, 0 ],
      [  0,   65,  141, 41, 34, 0, 0, 0 ],
      [  0,   53,  127, 56, 14, 0, 0, 0 ] ],
    [ [  4,   73,  132, 46, 31, 0, 0, 0 ],  // Unopposed
      [  1,   64,  143, 26, 13, 0, 0, 0 ],
      [  1,   47,  110, 44, 24, 0, 0, 0 ],
      [  0,   72,  127, 50, 31, 0, 0, 0 ] ],
    [ [  0,    0,   79, 23,  1, 0, 0, 0 ],  // BlockedByPawn
      [  0,    0,  148, 27,  2, 0, 0, 0 ],
      [  0,    0,  161, 16,  1, 0, 0, 0 ],
      [  0,    0,  171, 22, 15, 0, 0, 0 ] ],
    [ [ 22,   45,  104, 62,  6, 0, 0, 0 ],  // Unblocked
      [ 31,   30,   99, 39, 19, 0, 0, 0 ],
      [ 23,   29,   96, 41, 15, 0, 0, 0 ],
      [ 21,   23,  116, 41, 15, 0, 0, 0 ] ]
];


pub static mut CONNECTED: [[[[Score; RANK_CNT]; 3] ;2]; 2] = [[[[Score(0,0); RANK_CNT]; 3] ;2]; 2];

/// Initalizes the CONNECTED table.
#[cold]
pub fn init() {
    unsafe {
        let seed: [i32; 8] = [0, 13, 24, 18, 76, 100, 175, 330];
        for opposed in 0..2 {
            for phalanx in 0..2 {
                for support in 0..3 {
                    for r in 1..7 {
                        let mut v: i32 = 17 * support;
                        v += (seed[r] + (phalanx * ((seed[r as usize +1] - seed[r as usize]) / 2))) >> opposed;
                        let eg: i32 = v * (r as i32 - 2) / 4;
                        CONNECTED[opposed as usize][phalanx as usize][support as usize][r as usize] = Score(v, eg);
                    }
                }
            }
        }
    }
}

fn init_connected() -> [[[[Score; 2]; 2] ;3]; RANK_CNT] {
    let seed: [i32; 8] = [0, 13, 24, 18, 76, 100, 175, 330];
    let mut a: [[[[Score; 2]; 2] ;3]; 8] = [[[[Score(0,0); 2]; 2] ;3]; 8];
    for opposed in 0..2 {
        for phalanx in 0..2 {
            for support in 0..3 {
                for r in 1..7 {
                    let mut v: i32 = 17 * support;
                    v += (seed[r] + (phalanx * ((seed[r as usize +1] - seed[r as usize]) / 2))) >> opposed;
                    let eg: i32 = v * (r as i32 - 2) / 4;
                    a[r as usize][support as usize][phalanx as usize][opposed as usize] = Score(v, eg);
                }
            }
        }
    }
    a
}

/// Table to hold information about the pawn structure.
pub struct PawnTable {
    table: TableBase<PawnEntry>,
}

unsafe impl Send for PawnTable {}

impl PawnTable {
    /// Creates a new `PawnTable` of `size` entries.
    ///
    /// # Panics
    ///
    /// Panics if size is not a power of 2.
    pub fn new() -> Self {
        PawnTable {
            table: TableBase::new().unwrap()
        }
    }

    /// Retrieves the entry of a specified key. This method won't evaluate the resulting entry at all,
    /// so use sparingly.
    pub fn get(&mut self, key: u64) -> &mut PawnEntry {
        self.table.get_mut(key)
    }


    /// Clears the table and resets to another size.
    pub fn clear(&mut self) {
        self.table.clear();
    }

    /// Retrieves the entry of a specified key. If the `Entry` doesn't a matching key,
    /// the `Entry` will be evaluated for its pawn structure.
    pub fn probe(&mut self, board: &Board) -> &mut PawnEntry {
        let key: u64 = board.pawn_key();
        let entry = self.get(key);

        if entry.key == key {
            return entry;
        }

        entry.key = key;
        entry.score[Player::White as usize] = entry.evaluate::<WhiteType>(board);
        entry.score[Player::Black as usize] = entry.evaluate::<BlackType>(board);
        entry.open_files = (entry.semiopen_files[Player::White as usize]
            & entry.semiopen_files[Player::Black as usize]).count_ones() as u8;

        let all_passed: BitBoard = entry.passed_pawns[Player::White as usize]
            | entry.passed_pawns[Player::Black as usize];
        let exclusive_open_files = entry.semiopen_files[Player::White as usize]
            ^ entry.semiopen_files[Player::Black as usize];

        entry.asymmetry = (all_passed | BitBoard(exclusive_open_files as u64)).count_bits() as i16;
        entry
    }
}

impl PreFetchable for PawnTable {
    /// Pre-fetches a particular key. This means bringing it into the cache for faster eventual
    /// access.
    #[inline(always)]
    fn prefetch(&self, key: u64) {
        unsafe {
            let ptr = self.table.get_ptr(key);
            prefetch_write(ptr);
        }
    }

    #[inline(always)]
    fn prefetch2(&self, key: u64) {
        unsafe {
            let ptr = self.table.get_ptr(key);
            prefetch_write(ptr);
            let ptr_2 = (ptr as *mut u8).offset(64) as *const PawnEntry;
            prefetch_write(ptr_2);
        }
    }
}

/// Information on a the pawn structure for a given position.
///
/// This information is computed upon access.
pub struct PawnEntry {
    key: u64,
    score: [Score; PLAYER_CNT],
    passed_pawns: [BitBoard; PLAYER_CNT],
    pawn_attacks: [BitBoard; PLAYER_CNT],
    pawn_attacks_span: [BitBoard; PLAYER_CNT],
    king_squares: [SQ; PLAYER_CNT],
    king_safety_score: [Score; PLAYER_CNT],
    weak_unopposed: [i16; PLAYER_CNT],
    castling_rights: [Castling; PLAYER_CNT],
    semiopen_files: [u8; PLAYER_CNT],
    // per
    pawns_on_squares: [[u8; PLAYER_CNT]; PLAYER_CNT], // [color][light/dark squares]
    asymmetry: i16,
    open_files: u8
}

impl TableBaseConst for PawnEntry {
    const ENTRY_COUNT: usize = 16384;
}


impl PawnEntry {

    /// Returns the current score of the pawn structure.
    #[inline(always)]
    pub fn pawns_score(&self, player: Player) -> Score {
        self.score[player as usize]
    }

    /// Returns the possible pawn attacks `BitBoard` of a player.
    #[inline(always)]
    pub fn pawn_attacks(&self, player: Player) -> BitBoard {
        self.pawn_attacks[player as usize]
    }

    /// Returns the `BitBoard` of the passed pawns for a specified player. A passed pawn is one that
    /// has no opposing pawns in the same file, or any adjacent file.
    #[inline(always)]
    pub fn passed_pawns(&self, player: Player) -> BitBoard {
        self.passed_pawns[player as usize]
    }

    /// Returns the span of all the pawn's attacks for a given player.
    #[inline(always)]
    pub fn pawn_attacks_span(&self, player: Player) -> BitBoard {
        self.pawn_attacks_span[player as usize]
    }

    /// Returns the weak-unopposed score of the given player. This measures the strength of the pawn
    /// structure when considering isolated and disconnected pawns.
    #[inline(always)]
    pub fn weak_unopposed(&self, player: Player) -> i16 {
        self.weak_unopposed[player as usize]
    }

    /// Assymetric score of a position.
    #[inline(always)]
    pub fn asymmetry(&self) -> i16 {
        self.asymmetry
    }

    /// Returns a bitfield of the current ranks.
    #[inline(always)]
    pub fn open_files(&self) -> u8 {
        self.open_files
    }

    /// Returns if a file is semi-open for a given player, meaning there are no pieces of the
    /// opposing player on that file.
    #[inline]
    pub fn semiopen_file(&self, player: Player, file: File) -> bool {
        self.semiopen_files[player as usize] & (1 << file as u8) != 0
    }

    /// Returns if a side of a file is semi-open, meaning no enemy pieces.
    #[inline]
    pub fn semiopen_side(&self, player: Player, file: File, left_side: bool) -> bool {
        let side_mask: u8 = if left_side {
            file.left_side_mask()
        } else {
            file.right_side_mask()
        };
        self.semiopen_files[player as usize] & side_mask != 0
    }

    // returns count of pawns of a player on the same color square as the player's color.
    #[inline]
    pub fn pawns_on_same_color_squares(&self, player: Player, sq: SQ) -> u8 {
        self.pawns_on_squares[player as usize][sq.square_color_index()]
    }

    /// Returns the current king safety `Score` for a given player and king square.
    pub fn king_safety<P: PlayerTrait>(&mut self, board: &Board, ksq: SQ) -> Score {
        if self.king_squares[P::player_idx()] == ksq
            && self.castling_rights[P::player_idx()] == board.player_can_castle(P::player()) {
            self.king_safety_score[P::player_idx()]
        } else {
            self.king_safety_score[P::player_idx()] = self.do_king_safety::<P>(board, ksq);
            self.king_safety_score[P::player_idx()]
        }
    }

    fn do_king_safety<P: PlayerTrait>(&mut self, board: &Board, ksq: SQ) -> Score {
        self.king_squares[P::player_idx()] = ksq;
        self.castling_rights[P::player_idx()] = board.player_can_castle(P::player());
        let mut min_king_distance = 0;

        let pawns: BitBoard = board.piece_bb(P::player(), PieceType::P);
        if !pawns.is_empty() {
            while (ring_distance(ksq, min_king_distance as u8) & pawns).is_empty() {
                min_king_distance += 1;
            }
        }

        let mut bonus: Value = self.shelter_storm::<P>(board,ksq);

        if board.can_castle(P::player(),CastleType::KingSide) {
            bonus = bonus.max( self.shelter_storm::<P>(board, P::player().relative_square(SQ::G1)));
        }

        if board.can_castle(P::player(),CastleType::QueenSide) {
            bonus = bonus.max(self.shelter_storm::<P>(board, P::player().relative_square(SQ::C1)));
        }

        Score::new(bonus, -16 * min_king_distance)
    }


    fn shelter_storm<P: PlayerTrait>(&self, board: &Board, ksq: SQ) -> Value {
        let center: File = (File::B).max(File::G.min(ksq.file()));

        let mut b: BitBoard = board.piece_bb_both_players(PieceType::P)
            & (forward_rank_bb(P::player(), ksq.rank()) | ksq.rank_bb())
            & (adjacent_file(center) | SQ(center as u8).file_bb());

        let our_pawns: BitBoard = b & board.get_occupied_player(P::player());
        let their_pawns: BitBoard = b & board.get_occupied_player(P::opp_player());
        let mut safety: Value = MAX_SAFETY_BONUS;

        for file in ((center as u8) - 1)..((center as u8) + 2) {
            b = our_pawns & SQ(file).file_bb();
            let rk_us: Rank = if b.is_empty() {
                Rank::R1
            } else {
                P::player().relative_rank_of_sq(b.backmost_sq(P::player()))
            };


            b = their_pawns & SQ(file).file_bb();
            let rk_them: Rank = if b.is_empty() {
                Rank::R1
            } else {
                P::player().relative_rank_of_sq(b.frontmost_sq(P::opp_player()))
            };
            let d: File = unsafe { (transmute::<u8,File>(file)).min(!transmute::<u8,File>(file)) };

            // TODO: Simplify
            let r = if file == ksq.file() as u8 {
                1
            } else {
                0
            };

            let storm_danger_idx: usize = if file == ksq.file() as u8 && P::player().relative_rank_of_sq(ksq) as u8 + 1 == rk_them as u8 {
                0   // Blocked By King
            } else if rk_us == Rank::R1 {
                1  // Unopossed
            } else if rk_them as u8 == rk_us as u8 + 1 {
                2  // Blocked by Pawn
            } else {
                3  // Unblocked
            };

            safety -= SHELTER_WEAKNESS[r as usize][d as usize][rk_us as usize];
            safety -= STORM_DANGER[storm_danger_idx][d as usize][rk_them as usize];

        }
        safety
    }

    fn evaluate<P: PlayerTrait>(&mut self, board: &Board) -> Score {
        let mut b: BitBoard;
        let mut neighbours: BitBoard;
        let mut stoppers: BitBoard;
        let mut doubled: BitBoard;
        let mut supported: BitBoard;
        let mut phalanx: BitBoard;
        let mut lever: BitBoard;
        let mut lever_push: BitBoard;
        let mut opposed: bool;
        let mut backward: bool;

        let mut score: Score = Score::ZERO;
        let our_pawns: BitBoard = board.piece_bb(P::player(), PieceType::P);
        let their_pawns: BitBoard = board.piece_bb(P::opp_player(), PieceType::P);

        let mut p1: BitBoard = our_pawns;

        self.passed_pawns[P::player() as usize] =  BitBoard(0);
        self.pawn_attacks_span[P::player() as usize] = BitBoard(0);
        self.weak_unopposed[P::player() as usize] = 0;
        self.semiopen_files[P::player() as usize] = 0xFF;
        self.king_squares[P::player() as usize] = SQ::NO_SQ;
        self.pawn_attacks[P::player() as usize] = P::shift_up_left(our_pawns) | P::shift_up_right(our_pawns);

        let pawns_on_dark: u8 = (our_pawns & BitBoard::DARK_SQUARES).count_bits();
        self.pawns_on_squares[P::player() as usize][Player::Black as usize] = pawns_on_dark;
        self.pawns_on_squares[P::player() as usize][Player::White as usize] = board.count_piece(P::player(), PieceType::P) - pawns_on_dark;

        while let Some(s) = p1.pop_some_lsb() {
            assert_eq!(board.piece_at_sq(s), Piece::make_lossy(P::player(),PieceType::P));

            let f: File = s.file();

            self.semiopen_files[P::player() as usize] &= !(1 << f as u8);
            self.pawn_attacks[P::player() as usize] |= pawn_attacks_span(P::player(), s);

            opposed = (their_pawns & forward_file_bb(P::player(),s)).is_not_empty();
            stoppers = their_pawns & passed_pawn_mask(P::player(),s);
            lever = their_pawns & pawn_attacks_from(s, P::player());
            lever_push = their_pawns & pawn_attacks_from(P::up(s), P::player());
            doubled = our_pawns & (P::down(s)).to_bb();
            neighbours = our_pawns & adjacent_file(f);
            phalanx = neighbours & s.rank_bb();
            supported = neighbours & (P::down(s)).rank_bb();

            // A pawn is backward when it is behind all pawns of the same color on the
            // adjacent files and cannot be safely advanced.
            if neighbours.is_empty() || lever.is_not_empty()
                || P::player().relative_rank_of_sq(s) >= Rank::R5 {
                backward = false;
            } else {
                // Find the backmost rank with neighbours or stoppers
                b = (neighbours | stoppers).backmost_sq(P::player()).rank_bb();

                // The pawn is backward when it cannot safely progress to that rank:
                // either there is a stopper in the way on this rank, or there is a
                // stopper on adjacent file which controls the way to that rank.
                backward = ((b | P::shift_up(b & adjacent_file(f))) & stoppers)
                    .is_not_empty();

                assert!(!(backward && (forward_rank_bb(P::opp_player(), P::up(s).rank()) & neighbours).is_not_empty()));
            }

            // Passed pawns will be properly scored in evaluation because we need
            // full attack info to evaluate them. Include also not passed pawns
            // which could become passed after one or two pawn pushes when are
            // not attacked more times than defended.
            if    (stoppers ^ lever ^ lever_push).is_empty()
                && (our_pawns & forward_file_bb(P::player(),s)).is_empty()
                && supported.count_bits() as i8 >= lever.count_bits() as i8 - 1
                && phalanx.count_bits()   >= lever_push.count_bits() {
                self.passed_pawns[P::player() as usize] |= s.to_bb();

            } else if stoppers == P::up(s).to_bb() && P::player().relative_rank_of_sq(s) >= Rank::R5 {
                b = P::shift_up(supported) & !their_pawns;
                while let Some(b_sq) = b.pop_some_lsb() {
                    if !(their_pawns & pawn_attacks_from(b_sq, P::player())).more_than_one() {
                        self.passed_pawns[P::player() as usize] |= s.to_bb();
                    }
                }
            }

            if supported.is_not_empty() | supported.is_not_empty() {
                score += unsafe {
                    CONNECTED[opposed as usize]
                        [phalanx.is_not_empty() as usize]
                        [supported.count_bits() as usize]
                        [P::player().relative_rank_of_sq(s) as usize]
                };
            } else if neighbours.is_empty() {
                score -= ISOLATED;
                self.weak_unopposed[P::player() as usize] += (!opposed) as i16;
            } else if backward {
                score -= BACKWARDS;
                self.weak_unopposed[P::player() as usize] += (!opposed) as i16;
            }

            if doubled.is_not_empty() && supported.is_empty() {
                score -= DOUBLED;
            }
        }
        score
    }
}


#[cfg(test)]
mod tests {
    use super::*;
    use pleco::Board;

    #[test]
    fn pawn_eval() {
        let mut t: PawnTable = PawnTable::new();
        let boards: Vec<Board> = Board::random().pseudo_random(2222212).many(9);
        let mut score: i64 = 0;
        boards.iter().for_each(|b| {
            let entry = t.probe(b);
            score += entry.pawns_score(Player::White).0 as i64;
            score += entry.pawns_score(Player::Black).0 as i64;
        });
    }
}