Replace ctx->uPositional with a data-calibrated Eval() return value.

uPositional was a per-thread EWMA of abs(material - true score) used to
size lazy-eval and futility margins. It was history-derived (reflecting
whatever recent, unrelated positions looked like) rather than derived
from the position actually being margined, and its update/consumption
was tangled with EVAL_HASH (now disabled).

Eval() now takes an optional SCORE *piPositional out-param and fills it
in on every return path: exact (abs(material-delta)) on a full eval,
or an estimate from a new EstimatePositionalScore() on a lazy exit.
EstimatePositionalScore()'s two terms (king-safety-defect-bucketed, and
a flat residual for mobility/passers/everything else) are calibrated
from ~1.6M measured full-eval samples (p90 of the actual swing), not
guessed -- an initial guessed version measurably regressed ECM solve
rate (630 vs a 650 baseline at sn=4M); the recalibrated version is back
at parity (649/879).

search.c's qsearch futility now reads the value Eval() just computed
instead of the stale/shared ctx field. Also removes QSearchInDangerNoStandPat
and SideCanStandPat, dead since the danger-hash check that fed them was
already commented out (e08387a) -- they depended on the same enprise/
trapped-piece data this conversation is about to move off of
g_PositionHash entirely.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 4 insertions, 171 deletions

diff --git a/src/search.c b/src/search.c
index 0f814ea..4ea09b0 100755
--- a/src/search.c
+++ b/src/search.c
@@ -999,164 +999,6 @@ QSearchFromCheckNoStandPat(IN SEARCHER_THREAD_CONTEXT *ctx,
 }
 
 
-
-/**
-
-Routine description:
-
-    The QSearch (Quiescence Search) is a selective search called when
-    there is no remaining depth in Search.  Its job is to search only
-    moves that stabilize the position -- once it is quiescence (quiet)
-    we will run a static evaluation on it and return the score.
-
-    This branch of the QSearch is called when the side to move is in
-    danger somehow -- either he has two pieces en prise on the board
-    or some piece that seems trapped.  We do not allow him an
-    opportunity to stand pat in this position.
-
-Parameters:
-
-    IN SEARCHER_THREAD_CONTEXT *ctx,
-    IN SCORE iAlpha,
-    IN SCORE iBeta
-    IN SCORE iEval
-
-Return value:
-
-    SCORE
-
-**/
-SCORE
-QSearchInDangerNoStandPat(IN SEARCHER_THREAD_CONTEXT *ctx,
-                          IN SCORE iAlpha,
-                          IN SCORE iBeta)
-{
-    POSITION *pos = &ctx->sPosition;
-    CUMULATIVE_SEARCH_FLAGS *pf = &ctx->sSearchFlags;
-    ULONG x;
-    FLAG fIncludeChecks;
-    SCORE iBestScore = iAlpha;
-    SCORE iScore;
-    SCORE iFutility;
-    SCORE iEval = GetRoughEvalScore(ctx, iAlpha, iBeta, TRUE);
-    MOVE mv;
-    ULONG uLegalMoves = 0;
-    static ULONG _WhatToGen[] =
-    {
-        GENERATE_CAPTURES_PROMS,
-        GENERATE_CAPTURES_PROMS_CHECKS
-    };
-
-
-    // Set futility:
-    //
-    // iEval + move_value + margin < alpha
-    //         move_value          < alpha - margin - iEval
-    iFutility = 0;
-    if (iAlpha < +NMATE)
-    {
-        iFutility = (iAlpha -
-                     (FUTILITY_BASE_MARGIN + ctx->uPositional) -
-                     iEval);
-        iFutility = MAX0(iFutility);
-    }
-
-    // We suspect that the guy on move is in sad shape if we're
-    // here...  he has more than one piece en prise or he seems to
-    // have a piece trapped.  Allow him to play checks in order to try
-    // to save the situation.
-    ASSERT(!InCheck(pos, pos->uToMove));
-    fIncludeChecks = ((pf->uQsearchDepth < pf->uQsearchCheckDepth) &&
-                      (pf->fCouldStandPat[FLIP(pos->uToMove)] == FALSE));
-    GenerateMoves(ctx, NULLMOVE, _WhatToGen[fIncludeChecks]);
-
-    for (x = ctx->sMoveStack.uBegin[ctx->uPly];
-         x < ctx->sMoveStack.uEnd[ctx->uPly];
-         x++)
-    {
-        SelectBestNoHistory(ctx, x);
-        mv = ctx->sMoveStack.mvf[x].mv;
-#ifdef DEBUG
-        ASSERT(0 == (ctx->sMoveStack.mvf[x].bvFlags & MVF_MOVE_SEARCHED));
-        ctx->sMoveStack.mvf[x].bvFlags |= MVF_MOVE_SEARCHED;
-#endif
-
-        // Prune except when pruning all moves could cause us to return
-        // -INFINITY (mated) erroneously.
-        if (iAlpha > -INFINITY)
-        {
-            if (ctx->sMoveStack.mvf[x].iValue <= 0)
-            {
-                ASSERT(SanityCheckMoves(ctx, x, VERIFY_BEFORE | VERIFY_AFTER));
-                goto end;
-            }
-            if (FALSE == _ShouldWeConsiderThisMove(ctx,
-                                                   x,
-                                                   iFutility,
-                                                   TRUE))
-            {
-                continue;
-            }
-        }
-
-        if (FALSE == fIncludeChecks)
-        {
-            mv.bvFlags |= WouldGiveCheck(ctx, mv);
-        }
-
-        if (MakeMove(ctx, mv))
-        {
-            uLegalMoves++;
-            pf->uQsearchNodes++;
-            pf->uQsearchDepth++;
-            iScore = -QSearch(ctx,
-                              -iBeta,
-                              -iAlpha);
-            pf->uQsearchDepth--;
-            UnmakeMove(ctx, mv);
-            if (WE_SHOULD_STOP_SEARCHING) goto end;
-
-            if (iScore > iBestScore)
-            {
-                iBestScore = iScore;
-                ctx->sPlyInfo[ctx->uPly].mvBest = mv;
-                if (iScore > iAlpha)
-                {
-                    if (iScore >= iBeta)
-                    {
-                        KEEP_TRACK_OF_FIRST_MOVE_FHs(uLegalMoves == 1);
-                        ASSERT(SanityCheckMoves(ctx, x, VERIFY_BEFORE));
-                        goto end;
-                    }
-                    else
-                    {
-                        UpdatePV(ctx, mv);
-                        StoreExactScore(mv, pos, iScore, 0, FALSE, ctx->uPly);
-                        iAlpha = iScore;
-                    }
-                }
-            }
-        }
-    }
-    ASSERT(SanityCheckMoves(ctx, x, VERIFY_BEFORE));
-
- end:
-    // If iAlpha is -INFINITY and side on move has no captures,
-    // promotes or checks then we must make up a "stand pat" score
-    // here.  We don't want to let him stand pat with iEval because
-    // the board looks dangerous.  But we likewise don't want to say
-    // "mated" because he's not.
-    ASSERT((uLegalMoves > 0) || (iBestScore == iAlpha));
-    if (iBestScore == -INFINITY)
-    {
-        ASSERT(iAlpha == -INFINITY);
-        iBestScore = iEval - VALUE_QUEEN;
-    }
-    ASSERT(IS_VALID_SCORE(iBestScore) || WE_SHOULD_STOP_SEARCHING);
-    return(iBestScore);
-}
-
-
 /**
 
 Routine description:
@@ -1193,6 +1035,7 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
     SCORE iScore;
     SCORE iEval;
     SCORE iFutility;
+    SCORE iPositional;
     ULONG x;
     ULONG uLegalMoves;
     FLAG fIncludeChecks;
@@ -1269,16 +1112,6 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
     }
     ASSERT(!InCheck(pos, pos->uToMove));
 
-    // Even if the side is not in check, do not let him stand pat if
-    // his position looks dangerous (i.e. more than one piece en prise
-    // or a piece trapped).  Fail low if there's nothing that looks
-    // good on this line.
-    //if (SideCanStandPat(pos, pos->uToMove) == FALSE)
-    //{
-    //    iBestScore = QSearchInDangerNoStandPat(ctx, iAlpha, iBeta);
-    //    goto end;
-    //}
-
     // If we get here then side on move is not in check and this
     // position looks ok enough to allow him the option to stand pat
     // -or- we missed when we probed the dangerhash.  Also remember
@@ -1288,7 +1121,7 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
     // discovers a mate, there's no force since a stand pat
     // opportunity exists right here.
     uLegalMoves = 0;
-    iEval = iBestScore = Eval(ctx, iAlpha, iBeta);
+    iEval = iBestScore = Eval(ctx, iAlpha, iBeta, &iPositional);
     if (iBestScore > iAlpha)
     {
         iAlpha = iBestScore;
@@ -1312,7 +1145,7 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
     iFutility = 0;
     if (iAlpha < +NMATE)
     {
-        iFutility = iAlpha - (FUTILITY_BASE_MARGIN + ctx->uPositional) - iEval;
+        iFutility = iAlpha - (FUTILITY_BASE_MARGIN + iPositional) - iEval;
         iFutility = MAX0(iFutility);
     }
 
@@ -1400,7 +1233,7 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
                         {
                             iFutility = (iAlpha -
                                          (FUTILITY_BASE_MARGIN +
-                                          ctx->uPositional) -
+                                          iPositional) -
                                          iEval);
                             iFutility = MAX0(iFutility);
                         }