src/chess/pawn.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2016 Mike Becker. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
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 */

#include "pawn.h"
#include "rules.h"

bool pawn_chkrules(const GameState *gamestate, const Move *move) {
    int8_t d = piece_color(move->piece) == WHITE ? -1 : 1;
    
    if (move->torank == (d < 0 ? 7 : 0)) {
        if (move->promotion) {
            unsigned ppiecetype = piece_type(move->promotion);
            if (!ppiecetype || ppiecetype == PAWN || ppiecetype == KING) {
                return false;
            }
        } else {
            return false;
        }
    } else {
        if (move->promotion) {
            return false;
        }
    }
    
    if (move->capture) {
        if (move->fromrank == move->torank + d && (
            move->fromfile == move->tofile + 1 ||
            move->fromfile == move->tofile - 1)) {

            return piece_at(gamestate, move->torank, move->tofile) ||
                enpassant_threat_exists(gamestate, move->fromrank, move->tofile);
        } else {
            return false;
        }
    } else {
        if (move->fromfile == move->tofile) {
            return (move->fromrank == move->torank + d) ||
                (move->fromrank == (d < 0 ? 1 : 6) && /* advanced first move */
                move->fromrank == move->torank + d*2);
        } else {
            return false;
        }
    }
}

bool pawn_isblocked(const GameState *gamestate, const Move *move) {
    if (move->torank == move->fromrank + 1
        || move->torank == move->fromrank - 1) {
        return piece_at(gamestate, move->torank, move->tofile)
            && !move->capture;
    } else {
        return piece_at(gamestate, move->torank, move->tofile) ||
            gamestate->board[(move->fromrank + move->torank) / 2][move->tofile];
    }
}

size_t pawn_moves(const GameState *gamestate,
        Color c, Rank r, File f, Move *moves) {
    (void) gamestate; /* no (theoretical) move depends on the game state */
    size_t count = 0;
    int rankdelta = c == WHITE ? 1 : -1;
    int promotionrank = c == WHITE ? 7 : 0;
    int startrank = c == WHITE ? 1 : 6;
    const int targets[4][3] = {
        {r + rankdelta,     f, 0},
        {r + rankdelta, f - 1, 1},
        {r + rankdelta, f + 1, 1},
        {r + rankdelta * 2, f, 0}
    };

    for (size_t i = 0 ; i < 4 ; i++) {
        Rank rank = targets[i][0];
        File file = targets[i][1];

        if (i == 3 && r != startrank) {
            continue;
        }

        if (isidx(rank) && isidx(file)) {
            moves[count] = (Move){0};
            moves[count].piece = mkpiece(PAWN, c);
            moves[count].fromrank = r;
            moves[count].fromfile = f;
            moves[count].torank = rank;
            moves[count].tofile = file;
            moves[count].capture = targets[i][2];

            if (rank == promotionrank) {
                moves[count].promotion = mkpiece(QUEEN, c);
            }

            count++;
        }
    }

    return count;
}