testsAndMisc/C/lichess_random_engine/perft.c

#include "movegen.h"
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static unsigned long long perft(Position pos, int depth)
{
    if (depth == 0)
    {
        return 1ULL;
    }
    Move               moves[256];
    unsigned long long nodes = 0ULL;
    int                n     = gen_moves(&pos, moves, 256, 0);
    for (int i = 0; i < n; i++)
    {
        Position child = pos;
        Piece    cap   = EMPTY;
        make_move(&child, &moves[i], &cap);
        nodes += perft(child, depth - 1);
    }
    return nodes;
}

static void uci_from_move(const Move *m, char *buf)
{
    int ff = (m->from & 7);
    int fr = (m->from >> 4);
    int tf = (m->to & 7);
    int tr = (m->to >> 4);
    buf[0] = (char)('a' + ff);
    buf[1] = (char)('1' + fr);
    buf[2] = (char)('a' + tf);
    buf[3] = (char)('1' + tr);
    int i  = 4;
    if (m->promo)
    {
        char pc = 'q';
        switch (m->promo)
        {
        case WQ:
        case BQ:
            pc = 'q';
            break;
        case WR:
        case BR:
            pc = 'r';
            break;
        case WB:
        case BB:
            pc = 'b';
            break;
        case WN:
        case BN:
            pc = 'n';
            break;
        default:
            pc = 'q';
        }
        buf[i++] = pc;
    }
    buf[i] = 0;
}

static void run_case(const char *fen, int depth, unsigned long long expected)
{
    Position p;
    if (!parse_fen(&p, fen))
    {
        (void)fprintf(stderr, "Bad FEN: %s\n", fen);
        return;
    }
    unsigned long long n = perft(p, depth);
    printf("perft(%d) = %llu  %s\n", depth, n,
           (expected ? (n == expected ? "OK" : "MISMATCH") : ""));
}

int main(int argc, char **argv)
{
    if (argc >= 3)
    {
        const char *fen        = argv[1];
        char       *depth_end  = NULL;
        long        depth_long = strtol(argv[2], &depth_end, 10);
        if (depth_end == argv[2] || *depth_end != '\0' || depth_long < 0 || depth_long > INT_MAX)
        {
            (void)fprintf(stderr, "Invalid depth value: %s\n", argv[2]);
            return 1;
        }
        int      depth = (int)depth_long;
        Position p;
        if (!parse_fen(&p, fen))
        {
            (void)fprintf(stderr, "Bad FEN input\n");
            return 2;
        }
        if (argc >= 4 && strcmp(argv[3], "--divide") == 0)
        {
            Move               moves[256];
            int                n     = gen_moves(&p, moves, 256, 0);
            unsigned long long total = 0ULL;
            for (int i = 0; i < n; i++)
            {
                Position c   = p;
                Piece    cap = EMPTY;
                make_move(&c, &moves[i], &cap);
                unsigned long long sub = perft(c, depth - 1);
                char               u[8];
                uci_from_move(&moves[i], u);
                printf("%s: %llu\n", u, sub);
                total += sub;
            }
            printf("Total: %llu\n", total);
        }
        else if (argc >= 4 && strcmp(argv[3], "--divide-pseudo") == 0)
        {
            Move moves[256];
            int  n = gen_moves_pseudo(&p, moves, 256, 0);
            for (int i = 0; i < n; i++)
            {
                char u[8];
                uci_from_move(&moves[i], u);
                printf("%s\n", u);
            }
            printf("Total pseudo: %d\n", n);
        }
        else
        {
            unsigned long long n = perft(p, depth);
            printf("%llu\n", n);
        }
        return 0;
    }

    // Some well-known positions (depth limited to be fast). Expected nodes are standard perft
    // values. Start position
    run_case("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1", 1, 20ULL);
    run_case("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1", 2, 400ULL);
    // Kiwipete
    run_case("r3k2r/p1ppqpb1/bn2pnp1/2PpP3/1p2P3/2N2N2/PBPP1PPP/R2Q1RK1 w kq - 0 1", 1, 48ULL);
    run_case("r3k2r/p1ppqpb1/bn2pnp1/2PpP3/1p2P3/2N2N2/PBPP1PPP/R2Q1RK1 w kq - 0 1", 2, 2039ULL);
    // Simple EP
    run_case("rnbqkbnr/pppppppp/8/8/3Pp3/8/PPP1PPPP/RNBQKBNR b KQkq d3 0 1", 1, 29ULL);
    return 0;
}