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-rwxr-xr-xsrc/search.c129
1 files changed, 49 insertions, 80 deletions
diff --git a/src/search.c b/src/search.c
index ff7e661..00b37f2 100755
--- a/src/search.c
+++ b/src/search.c
@@ -153,7 +153,7 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
ULONG uStage = TRY_HASH_MOVE;
ULONG u;
ULONG uFutilityMargin = 0;
- SCORE iMoveSee = 0;
+ SCORE iCheckSee;
#ifdef DEBUG
ASSERT(IS_VALID_SCORE(iAlpha));
ASSERT(IS_VALID_SCORE(iBeta));
@@ -167,8 +167,15 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
mvBest.uMove = 0;
// Jump directly to Qsearch if remaining depth is low enough.
- // This is the only place Qsearch is entered.
- if (uDepth < ONE_PLY)
+ // This is the only place Qsearch is entered. Lowered from ONE_PLY to
+ // THREE_QUARTERS_PLY to match the check extension's new flat amount
+ // (searchsup.c's ComputeMoveExtension) -- a lone check (or short run
+ // of them) still buys exactly one extra full-width ply as before, but
+ // a long unbroken chain now pays QUARTER_PLY of real cost per check
+ // instead of extending for free. root.c compensates by trimming the
+ // same QUARTER_PLY off the per-iteration depth budget so this doesn't
+ // just add a blanket 1/4 ply to every search.
+ if (uDepth < THREE_QUARTERS_PLY)
{
pf->fCouldStandPat[BLACK] = pf->fCouldStandPat[WHITE] = FALSE;
pf->uQsearchNodes = pf->uQsearchDepth = 0;
@@ -192,7 +199,6 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
}
DTEnterNode(ctx, uDepth, FALSE, iAlpha, iBeta);
iInitialAlpha = iAlpha;
- pi->fIsPVNode = (iBeta != iAlpha + 1);
ASSERT((IS_CHECKING_MOVE(mvLast) && (TRUE == pi->fInCheck)) ||
(!IS_CHECKING_MOVE(mvLast) && (FALSE == pi->fInCheck)));
@@ -430,19 +436,8 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
// prune away moves we will also make sure there is
// no per-move extension.
ASSERT(!uFutilityMargin);
- // Narrowed from "<= TWO_PLY" to "< TWO_PLY": ExtraReduction's
- // own safety cap guarantees a reduced move's child lands
- // with remaining depth >= TWO_PLY, which used to hand every
- // heavily-reduced line straight into futility's activation
- // floor at exactly that value -- double jeopardy on the
- // same move by construction, not by chance. Excluding just
- // that exact floor value (not the whole fractional-depth
- // window below it) un-stacks that specific overlap.
- if (FALSE && // EXPERIMENT: disabled for the unscaled-LMR-table
- // test -- isolate the new reduction table's
- // effect without also stacking futility pruning
- (iRoughEval + VALUE_ROOK <= iAlpha) &&
- (uDepth < TWO_PLY) &&
+ if ((iRoughEval + VALUE_ROOK <= iAlpha) &&
+ (uDepth <= TWO_PLY) &&
(ctx->uPly >= 2) &&
(iOrigExtend == 0) &&
(ctx->sPlyInfo[ctx->uPly - 2].iExtensionAmount <= 0) &&
@@ -530,14 +525,15 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
}
#endif
- // SEE must be computed on the PRE-move position (it internally
- // simulates removing mv.pMoved from mv.cFrom and adding x-rays --
- // see see.c) -- so grab it now, before MakeMove mutates *pos in
- // place, for the futility check below to use. Only bother when
- // futility mode is actually active at this node.
- if (uFutilityMargin)
+ // SEE must be computed on the PRE-move position -- see.c's
+ // exchange walk needs the piece still sitting on cFrom. Only
+ // needed for checking moves, where ComputeMoveExtension uses it
+ // to gate the check extension on soundness (Crafty-style: don't
+ // extend a checking move that's really just a losing sacrifice).
+ iCheckSee = 0;
+ if (IS_CHECKING_MOVE(mv))
{
- iMoveSee = SEE(pos, mv);
+ iCheckSee = SEE(pos, mv);
}
if (TRUE == MakeMove(ctx, mv))
@@ -555,6 +551,7 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
(x - 1), // Note: x==0 if doing mvHash
iRoughEval,
uDepth,
+ iCheckSee,
&iExtend);
// Cap how many extension plies this line may spend in total
@@ -579,22 +576,11 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
iExtend))
{
ASSERT(iExtend == 0);
- iExtend = -(ONE_PLY + ExtraReduction(uDepth, (x - 1),
- GetMoveFailHighPercentage(mv)));
- pi->iExtensionAmount = iExtend;
- INC(ctx->sCounters.tree.u64HistoryPrunes);
+ iExtend = -ONE_PLY;
+ pi->iExtensionAmount = -ONE_PLY;
}
- // Maybe even "futility prune" this move away. Require two
- // independent corroborating signals on top of the static
- // margin, not just the move's ordering score alone: this
- // specific move must have rarely caused a beta cutoff
- // historically (same threshold WeShouldDoHistoryPruning
- // uses), and it must not show a tactical gain per SEE --
- // ComputeMoveScore alone is PSQT/history/killer-bonus for
- // quiet moves, with no exchange evaluation at all, so it
- // was pruning purely on a positional-ordering number.
-#ifdef PERF_COUNTERS
+ // Maybe even "futility prune" this move away.
if ((x != 0) &&
(uLegalMoves > 1) &&
(uFutilityMargin) &&
@@ -602,25 +588,6 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
(iExtend <= 0) &&
(!IS_ESCAPING_CHECK(mv)))
{
- INC(ctx->sCounters.tree.u64FutilityCandidates);
- }
-#endif
- if ((x != 0) &&
- (uLegalMoves > 1) &&
- (uFutilityMargin) &&
- (ComputeMoveScore(ctx, mv, (x - 1)) < uFutilityMargin) &&
- (iExtend <= 0) &&
- (!IS_ESCAPING_CHECK(mv)) &&
- // Stricter than WeShouldDoHistoryPruning's <= 10: that one
- // gates a reduction with a fail-high re-search safety net
- // (search.c's own counters show ~2% wrong-guess rate is
- // fine there); this gates an outright, unverified skip --
- // no re-search, no recovery if wrong -- so demand much
- // stronger evidence the move is truly hopeless.
- (GetMoveFailHighPercentage(mv) <= 3) &&
- (iMoveSee <= 0))
- {
- INC(ctx->sCounters.tree.u64FutilityPrunes);
// TODO: test this more carefully
ASSERT(!IS_CHECKING_MOVE(mv));
UnmakeMove(ctx, mv);
@@ -652,9 +619,8 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
// Research deeper if history pruning failed
if ((iExtend < 0) && (iScore >= iBeta))
{
- uNextDepth -= iExtend; // undo the full reduction, whatever its magnitude
+ uNextDepth += ONE_PLY;
pi->iExtensionAmount = 0;
- INC(ctx->sCounters.tree.u64HistoryPruneReSearches);
iScore = -Search(ctx, -iBeta, -iAlpha, uNextDepth);
}
UnmakeMove(ctx, mv);
@@ -946,20 +912,19 @@ QSearchFromCheckNoStandPat(IN SEARCHER_THREAD_CONTEXT *ctx,
uMoveCount = MOVE_COUNT(ctx, ctx->uPly);
if (uMoveCount > 0)
{
- // Consider extending the number of qsearch plies we consider
- // non-capture checks at during this line.
- if ((pf->fCouldStandPat[pos->uToMove] == FALSE) &&
- (pf->uQsearchDepth < g_uIterateDepth / 2) &&
- (CountKingSafetyDefects(pos, pos->uToMove) > 1))
+ // Consider extending the number of qsearch plies for our opponent
+ // if this looks good.
+ if ((pf->uQsearchDepth < pf->uQsearchCheckDepth) &&
+ (pf->uQsearchDepth < g_uIterateDepth / 4) &&
+ (pf->fCouldStandPat[pos->uToMove] == FALSE) &&
+ (CountKingSafetyDefects(pos, pos->uToMove) > 2))
{
- if (uMoveCount == 1) {
+ if ((uMoveCount == 1) ||
+ (NUM_KING_MOVES(ctx, ctx->uPly) == 0) ||
+ (NUM_CHECKING_PIECES(ctx, ctx->uPly) > 1))
+ {
uQsearchCheckExtension = 2;
INC(ctx->sCounters.extension.uQExtend);
- } else if ((uMoveCount == 2) ||
- (NUM_KING_MOVES(ctx, ctx->uPly) == 0) ||
- (NUM_CHECKING_PIECES(ctx, ctx->uPly) > 1)) {
- uQsearchCheckExtension = 1;
- INC(ctx->sCounters.extension.uQExtend);
}
ctx->sPlyInfo[ctx->uPly].iExtensionAmount = uQsearchCheckExtension;
}
@@ -1080,7 +1045,7 @@ QSearchInDangerNoStandPat(IN SEARCHER_THREAD_CONTEXT *ctx,
// Set futility:
- //
+ //
// iEval + move_value + margin < alpha
// move_value < alpha - margin - iEval
iFutility = 0;
@@ -1097,7 +1062,8 @@ QSearchInDangerNoStandPat(IN SEARCHER_THREAD_CONTEXT *ctx,
// 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 < g_uIterateDepth / 3);
+ fIncludeChecks = ((pf->uQsearchDepth < pf->uQsearchCheckDepth) &&
+ (pf->fCouldStandPat[FLIP(pos->uToMove)] == FALSE));
GenerateMoves(ctx, NULLMOVE, _WhatToGen[fIncludeChecks]);
for (x = ctx->sMoveStack.uBegin[ctx->uPly];
@@ -1313,7 +1279,10 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
// position looks ok enough to allow him the option to stand pat
// -or- we missed when we probed the dangerhash. Also remember
// that this side has had the option to stand pat when searching
- // below this point.
+ // below this point. This also means the other side is not
+ // allowed to generate checks on this side because even if it
+ // discovers a mate, there's no force since a stand pat
+ // opportunity exists right here.
uLegalMoves = 0;
iEval = iBestScore = Eval(ctx, iAlpha, iBeta);
if (iBestScore > iAlpha)
@@ -1343,13 +1312,13 @@ QSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
iFutility = MAX0(iFutility);
}
- // We know we are not in check. Generate moves (including checks
- // if we are below the threshold and the other side has never been
- // allowed to stand pat). Recurse.
- fIncludeChecks = ((pf->uQsearchDepth < pf->uQsearchCheckDepth) &&
- (pf->fCouldStandPat[FLIP(pos->uToMove)] == FALSE) &&
- (pos->uNonPawnMaterial[pos->uToMove] >
- (VALUE_KING + VALUE_BISHOP)));
+ // We know we are not in check. If we are early in the qsearch,
+ // and the other side has not yet been able to stand pat, and we
+ // have material, generate checks here too.
+ fIncludeChecks =
+ ((pf->uQsearchDepth < pf->uQsearchCheckDepth) &&
+ (pf->fCouldStandPat[FLIP(pos->uToMove)] == FALSE) &&
+ (pos->uNonPawnMaterial[pos->uToMove] > (VALUE_KING + VALUE_BISHOP)));
GenerateMoves(ctx, NULLMOVE, _WhatToGen[fIncludeChecks]);
for (x = ctx->sMoveStack.uBegin[ctx->uPly];
x < ctx->sMoveStack.uEnd[ctx->uPly];
generated by cgit v1.3 (git 2.53.0) at 2026-09-10 03:26:21 +0000