path: root/src/probe.c

/**

Copyright (c) Scott Gasch

Module Name:

    probe.c

Abstract:

    Routines for probing endgame tablebases.  This uses Ronald de
    Man's Syzygy tablebase format via Jon Dart's "Fathom" probing
    library (see fathom/) instead of Eugene Nalimov's original
    tablebases.  Syzygy tables store WDL (win/draw/loss) + DTZ
    (distance to zeroing move) rather than Nalimov's DTM (distance
    to mate); they are dramatically smaller on disk and the probing
    code is far simpler as a result.  We lose literal mate-distance
    information from interior-node probes, so a probed win/loss is
    reported as a large-but-not-mate-range score rather than a
    precise mate score.

Author:

    Scott Gasch ([email protected]) 02 Jul 2004
    Converted to Syzygy/Fathom 23 Aug 2026

Revision History:

    $Id: probe.c 355 2008-07-01 15:46:43Z scott $

**/

#include "chess.h"
#include "fathom/tbprobe.h"

ULONG g_uEgtbLock = 0;

//
// A probed tablebase win/loss doesn't carry a real distance-to-mate
// (Syzygy WDL doesn't encode one), so we report a large decisive
// score that stays safely below NMATE.  This keeps it from being
// mistaken for (and ply-adjusted as) a literal forced mate elsewhere
// in the engine while still dominating ordinary evaluation scores.
//
#define EGTB_WIN_SCORE              (NMATE - VALUE_QUEEN)
#define EGTB_LOSS_SCORE             (-EGTB_WIN_SCORE)

static FLAG g_fEgtbInitialized = FALSE;

void
InitializeEGTB(void)
/**

Routine description:

    [Re]Initialize the Syzygy EGTB system.  Called during system
    startup and when the user uses "set" to change the EGTB path.

Parameters:

    void (uses g_Options.szEGTBPath)

Return value:

    void

**/
{
    CHAR *szPath = g_Options.szEGTBPath;

    if (TRUE == g_fEgtbInitialized)
    {
        tb_free();
        g_fEgtbInitialized = FALSE;
    }

    if ((szPath != NULL) && strlen(szPath) > 0)
    {
        if (TRUE == tb_init(szPath))
        {
            g_fEgtbInitialized = TRUE;
            if (TB_LARGEST > 0)
            {
                Trace("Found Syzygy endgame tablebases (up to %u men).\n\n",
                      TB_LARGEST);
            }
        }
    }
}

void
CleanupEGTB(void)
/**

Routine description:

    Cleanup the Syzygy EGTB system.

Parameters:

    void

Return value:

    void

**/
{
    if (TRUE == g_fEgtbInitialized)
    {
        tb_free();
        g_fEgtbInitialized = FALSE;
    }
}


static void
_BuildFathomBitboards(IN POSITION *pos,
                      OUT UINT64 *pu64White,
                      OUT UINT64 *pu64Black,
                      OUT UINT64 *pu64Kings,
                      OUT UINT64 *pu64Queens,
                      OUT UINT64 *pu64Rooks,
                      OUT UINT64 *pu64Bishops,
                      OUT UINT64 *pu64Knights,
                      OUT UINT64 *pu64Pawns)
/**

Routine description:

    Build the set of bitboards Fathom's tb_probe_wdl wants out of our
    POSITION.  Fathom expects the standard tablebase square numbering
    (a1 == bit 0 ... h8 == bit 63), which is exactly what our TO64()
    macro produces -- note this is *not* the same square numbering as
    our engine's own internal BBSQUARE/COOR_TO_BB bitboards, so we
    must not use those macros here.

Parameters:

    POSITION *pos,
    UINT64 *pu64White ... pu64Pawns

Return value:

    static void

**/
{
    ULONG uColor;
    ULONG u;
    COOR c;
    PIECE p;
    UINT64 bb;

    *pu64White = *pu64Black = 0ULL;
    *pu64Kings = *pu64Queens = *pu64Rooks = 0ULL;
    *pu64Bishops = *pu64Knights = *pu64Pawns = 0ULL;

    for (uColor = BLACK; uColor <= WHITE; uColor++)
    {
        UINT64 *pu64Side = (uColor == WHITE) ? pu64White : pu64Black;

        for (u = 0; u < pos->uPawnCount[uColor]; u++)
        {
            c = pos->cPawns[uColor][u];
            ASSERT(IS_ON_BOARD(c));
            bb = (1ULL << (TO64(c)));
            *pu64Side |= bb;
            *pu64Pawns |= bb;
        }

        for (u = 0; u < pos->uNonPawnCount[uColor][0]; u++)
        {
            c = pos->cNonPawns[uColor][u];
            ASSERT(IS_ON_BOARD(c));
            bb = (1ULL << (TO64(c)));
            *pu64Side |= bb;

            if (0 == u)
            {
                ASSERT(IS_KING(pos->rgSquare[c].pPiece));
                *pu64Kings |= bb;
                continue;
            }

            p = pos->rgSquare[c].pPiece;
            ASSERT(p && !IS_PAWN(p) && !IS_KING(p));
            if (IS_KNIGHT(p)) *pu64Knights |= bb;
            else if (IS_BISHOP(p)) *pu64Bishops |= bb;
            else if (IS_ROOK(p)) *pu64Rooks |= bb;
            else
            {
                ASSERT(IS_QUEEN(p));
                *pu64Queens |= bb;
            }
        }
    }
}


FLAG
ProbeEGTB(SEARCHER_THREAD_CONTEXT *ctx,
          SCORE *piScore)
/**

Routine description:

    Search for a board position in the Syzygy EGTB files on disk via
    Fathom.  This only returns a WDL (win/draw/loss) result, not a
    literal mate distance -- see EGTB_WIN_SCORE / EGTB_LOSS_SCORE.

Parameters:

    SEARCHER_THREAD_CONTEXT *ctx,
    SCORE *piScore

Return value:

    FLAG

**/
{
    POSITION *pos = &(ctx->sPosition);
    UINT64 u64White, u64Black, u64Kings, u64Queens;
    UINT64 u64Rooks, u64Bishops, u64Knights, u64Pawns;
    unsigned uEp;
    unsigned uWdl;
    ULONG wcount, bcount;
    FLAG fResult;

    if (FALSE == g_fEgtbInitialized || 0 == TB_LARGEST)
    {
        return(FALSE);
    }

    //
    // Syzygy WDL probing requires no castling rights on the board and
    // a zero halfmove (fifty move rule) clock; the WDL tables don't
    // encode either.
    //
    if ((0 != pos->bvCastleInfo) || (0 != pos->uFifty))
    {
        return(FALSE);
    }

    wcount = pos->uNonPawnCount[WHITE][0] + pos->uPawnCount[WHITE];
    bcount = pos->uNonPawnCount[BLACK][0] + pos->uPawnCount[BLACK];
    if ((wcount + bcount) > TB_LARGEST)
    {
        return(FALSE);
    }
    INC(ctx->sCounters.egtb.uProbes);

    _BuildFathomBitboards(pos, &u64White, &u64Black, &u64Kings, &u64Queens,
                          &u64Rooks, &u64Bishops, &u64Knights, &u64Pawns);

    uEp = 0;
    if (IS_ON_BOARD(pos->cEpSquare))
    {
        uEp = TO64(pos->cEpSquare);
    }

    AcquireSpinLock(&g_uEgtbLock);
    uWdl = tb_probe_wdl(u64White, u64Black, u64Kings, u64Queens, u64Rooks,
                        u64Bishops, u64Knights, u64Pawns,
                        /* rule50 */ 0, /* castling */ 0, uEp,
                        (pos->uToMove == WHITE));
    ReleaseSpinLock(&g_uEgtbLock);

    if (TB_RESULT_FAILED == uWdl)
    {
        return(FALSE);
    }

    switch (uWdl)
    {
        case TB_WIN:
            *piScore = EGTB_WIN_SCORE;
            break;
        case TB_LOSS:
            *piScore = EGTB_LOSS_SCORE;
            break;
        case TB_CURSED_WIN:
        case TB_BLESSED_LOSS:
        case TB_DRAW:
        default:
            *piScore = g_iDrawScore[pos->uToMove];
            break;
    }
    fResult = TRUE;

#ifdef PERF_COUNTERS
    INC(ctx->sCounters.egtb.uHits);
#endif
    return(fResult);
}


//
// Convert a Fathom tablebase square index (a1==0 ... h8==63) back into
// our own COOR encoding.  Inverse of TO64().
//
#define FROM64(s)                   \
    ((((7 - ((s) >> 3)) << 4)) | ((s) & 0x7))


static PIECE
_TbPromotesToPiece(IN unsigned uPromotes)
/**

Routine description:

    Map a TB_PROMOTES_* value from a Fathom root probe result to our
    own PIECE constant.

Parameters:

    unsigned uPromotes

Return value:

    static PIECE

**/
{
    switch (uPromotes)
    {
        case TB_PROMOTES_QUEEN:  return(QUEEN);
        case TB_PROMOTES_ROOK:   return(ROOK);
        case TB_PROMOTES_BISHOP: return(BISHOP);
        case TB_PROMOTES_KNIGHT: return(KNIGHT);
        default:                 return(0);
    }
}


FLAG
ProbeEGTBRoot(SEARCHER_THREAD_CONTEXT *ctx,
              MOVE *pmv,
              SCORE *piScore)
/**

Routine description:

    Probe the Syzygy DTZ tables for the best move at the root.  Unlike
    ProbeEGTB (WDL-only, used at interior nodes), this uses DTZ to
    pick a move that actually makes progress towards mate / the
    fifty-move-rule reset -- Syzygy WDL alone has no notion of "closer
    to mate" so relying on it exclusively could shuffle forever inside
    a won position.  This is expected to be called once at the root,
    before the normal iterative search, when <= TB_LARGEST pieces
    remain on the board.

    We ask Fathom for its suggested (from, to, promotion) and then
    find the matching move in our own already-generated root move
    list, rather than reconstructing a MOVE by hand, so we inherit our
    engine's own move flags (capture, en passant, special, etc).

Parameters:

    SEARCHER_THREAD_CONTEXT *ctx,
    MOVE *pmv,
    SCORE *piScore

Return value:

    FLAG : TRUE if a move was found and *pmv / *piScore were set.

**/
{
    POSITION *pos = &(ctx->sPosition);
    UINT64 u64White, u64Black, u64Kings, u64Queens;
    UINT64 u64Rooks, u64Bishops, u64Knights, u64Pawns;
    unsigned uEp;
    unsigned uResult;
    unsigned uWdl;
    COOR cFrom, cTo;
    PIECE pPromotes;
    ULONG wcount, bcount;
    ULONG u;

    if (FALSE == g_fEgtbInitialized || 0 == TB_LARGEST)
    {
        return(FALSE);
    }

    wcount = pos->uNonPawnCount[WHITE][0] + pos->uPawnCount[WHITE];
    bcount = pos->uNonPawnCount[BLACK][0] + pos->uPawnCount[BLACK];
    if ((wcount + bcount) > TB_LARGEST)
    {
        return(FALSE);
    }

    _BuildFathomBitboards(pos, &u64White, &u64Black, &u64Kings, &u64Queens,
                          &u64Rooks, &u64Bishops, &u64Knights, &u64Pawns);

    uEp = 0;
    if (IS_ON_BOARD(pos->cEpSquare))
    {
        uEp = TO64(pos->cEpSquare);
    }

    AcquireSpinLock(&g_uEgtbLock);
    uResult = tb_probe_root(u64White, u64Black, u64Kings, u64Queens, u64Rooks,
                            u64Bishops, u64Knights, u64Pawns,
                            pos->uFifty, pos->bvCastleInfo, uEp,
                            (pos->uToMove == WHITE), NULL);
    ReleaseSpinLock(&g_uEgtbLock);

    if ((TB_RESULT_FAILED == uResult) ||
        (TB_RESULT_CHECKMATE == uResult) ||
        (TB_RESULT_STALEMATE == uResult))
    {
        //
        // No usable move (either failed, or the earlier terminal-state
        // check already handles checkmate/stalemate).
        //
        return(FALSE);
    }

    //
    // A blessed win / cursed loss / plain draw at the root: don't
    // steer the search away from its own move choice, since these
    // are all draws under the fifty move rule and normal search
    // handles that correctly already.  Only override the root move
    // when this is a clear win or a position we must play carefully
    // to avoid losing (both cases: follow the DTZ suggestion).
    //
    uWdl = TB_GET_WDL(uResult);
    if ((TB_DRAW == uWdl) ||
        (TB_CURSED_WIN == uWdl) ||
        (TB_BLESSED_LOSS == uWdl))
    {
        return(FALSE);
    }

    cFrom = FROM64(TB_GET_FROM(uResult));
    cTo = FROM64(TB_GET_TO(uResult));
    pPromotes = _TbPromotesToPiece(TB_GET_PROMOTES(uResult));

    for (u = ctx->sMoveStack.uBegin[ctx->uPly];
         u < ctx->sMoveStack.uEnd[ctx->uPly];
         u++)
    {
        MOVE mv = ctx->sMoveStack.mvf[u].mv;
        if ((mv.cFrom == cFrom) &&
            (mv.cTo == cTo) &&
            (mv.pPromoted == pPromotes))
        {
            *pmv = mv;
            *piScore = (TB_WIN == uWdl) ? EGTB_WIN_SCORE : EGTB_LOSS_SCORE;
            return(TRUE);
        }
    }

    //
    // Fathom suggested a move we couldn't find in our own move list;
    // this shouldn't happen for a legally-generated root, but don't
    // trust it if it does.
    //
    ASSERT(FALSE);
    return(FALSE);
}