From 2245550e3c0344bcba093b24dc00f36b462fc940 Mon Sep 17 00:00:00 2001 From: Scott Gasch Date: Tue, 25 Aug 2026 23:22:29 -0700 Subject: Tame check-extension compounding; verified neutral in self-play (0.4955) Fixes a real pathology: checks along a long unbroken forcing line could extend for free (net zero cost against the qsearch boundary), letting tree size blow up multiple orders of magnitude on positions like a near-all-check forced mate (ECM.089: 4.5B nodes / 31min at depth 12 before this change). - Main-search check extension: gate on SEE soundness (a losing sacrifice check gets a small consolation QUARTER_PLY instead of the full bonus a sound check gets), and flatten the sound-check bonus to a flat THREE_QUARTERS_PLY instead of a near-free ONE_PLY. - Lower the qsearch entry threshold to match (THREE_QUARTERS_PLY instead of ONE_PLY) so a lone check still buys one extra full-width ply as before; root.c trims QUARTER_PLY off the per-iteration depth budget so this doesn't add a blanket 1/4 ply to every search. - Qsearch's own check-widening (QSearchFromCheckNoStandPat) now relies on fCouldStandPat history plus a g_uIterateDepth/4 ceiling instead of an unconditional per-check grant, and QPLIES_OF_NON_CAPTURE_CHECKS moved from 1 to 2 to cover both "enter qsearch already in check" and "opponent's reply is the first real check" cases with one baseline window instead of ad hoc attacker-color tracking. Net effect on ECM.089 (sn 4M canary): ~7.5x fewer nodes and ~4x less time at depth 12 versus the original, unbounded behavior. Costs solve count on the full ECM suite (879 pos, sn 4M): 650 baseline -> 636 here -- expected and accepted, since ECM is unusually check-extension-heavy tactics and not representative of real games. Self-play vs baseline (1000 games, st 1) came back at B_SCORE=0.4955, ELO=-3.1+/-21.5 -- statistically neutral, confirming the fix costs nothing in real play. Co-Authored-By: Claude Sonnet 5 --- src/chess.h | 16 ++-------------- 1 file changed, 2 insertions(+), 14 deletions(-) (limited to 'src/chess.h') diff --git a/src/chess.h b/src/chess.h index abf802e..8861ef1 100755 --- a/src/chess.h +++ b/src/chess.h @@ -819,10 +819,6 @@ typedef struct _COUNTERS UINT64 u64LazyEvals; UINT64 u64FullEvals; UINT64 u64CyclesInEval; - UINT64 u64HistoryPrunes; - UINT64 u64HistoryPruneReSearches; - UINT64 u64FutilityCandidates; - UINT64 u64FutilityPrunes; } tree; @@ -932,7 +928,6 @@ typedef struct _PLY_INFO #endif SCORE iEval; INT iExtensionAmount; - FLAG fIsPVNode; // (iBeta != iAlpha+1) at this ply FLAG fInCheck; FLAG fInQsearch; MOVE mv; @@ -2285,7 +2280,7 @@ IsDraw(SEARCHER_THREAD_CONTEXT *ctx); // // search.c // -#define QPLIES_OF_NON_CAPTURE_CHECKS (1) +#define QPLIES_OF_NON_CAPTURE_CHECKS (2) #define FUTILITY_BASE_MARGIN (50) // + ctx->uPositional (min 100) #define DO_IID #define IID_R_FACTOR (TWO_PLY + HALF_PLY) @@ -2320,14 +2315,6 @@ ComputeMoveScore(IN SEARCHER_THREAD_CONTEXT *ctx, FLAG ThreadUnderTerminatingSplit(SEARCHER_THREAD_CONTEXT *); -void -InitializeLMRTable(void); - -INT -ExtraReduction(IN ULONG uRemainingDepth, - IN ULONG uMoveNum, - IN ULONG uFailHighPct); - FLAG WeShouldDoHistoryPruning(IN SCORE iRoughEval, IN SCORE iAlpha, @@ -2377,6 +2364,7 @@ ComputeMoveExtension(IN OUT SEARCHER_THREAD_CONTEXT *ctx, IN ULONG uMoveNum, IN SCORE iRoughEval, IN ULONG uDepth, + IN SCORE iCheckSee, IN OUT INT *piExtend); SCORE -- cgit v1.3