From 538df17868afff51d49927fb5c8a91724752f26c Mon Sep 17 00:00:00 2001 From: Scott Gasch Date: Fri, 28 Aug 2026 08:29:09 -0700 Subject: Fix _ShouldWeConsiderThisMove's SEE-purity bug and ComputeMoveScore's killer-mate edge case; fix PV-display cycle hang. _ShouldWeConsiderThisMove (QSearch's move-consider gate) read the raw, move-ordering-biased mvf[].iValue directly instead of going through ComputeMoveScore, so it inherited the same +120-ish flat bias (plus small MVV-LVA nudges) on winning/even captures that ComputeMoveScore was already fixed to strip out. Fixed via the same MOVE_SCORE_ORDERING_BIAS subtraction, now factored into a shared chess.h macro. Restoring the old effective leniency required an explicit QSEARCH_CONSIDER_MARGIN (120, A/B'd against 0/60/120 on ecm_ringers/confident_quick/hard_quick) rather than assuming the bug's magnitude was itself a meaningful margin -- net effect vs the pre-fix baseline is -2 solves on hard_quick, accepted as the cost of correctness (see lmr_testing/RESULTS.md for the full sweep). ComputeMoveScore separately mishandled quiet killer-mate moves: they can reach SORT_THESE_FIRST via generate.c's killer-mate bonus (unrelated to the capture-bias path), so the bias-subtraction was wrongly applied to a move that never had that bias. Gated the subtraction on IS_CAPTURE_OR_PROMOTION(mv); quiet moves (including killer-mate ones) now correctly collapse to 0, per the function's contract of estimating a move's value on the 100=1-pawn axis. Measured as a no-op on all three suites -- rare in practice, but a real correctness fix. Left a comment documenting two candidate refinements for scoring quiet moves as non-uniform future work, deliberately not implemented (each needs its own isolated test). FinishPVTailFromHash (cosmetic PV-display hash-walk, used only for printing) had no cycle detection, so a drawish/repeating position could spin until the output buffer filled instead of terminating naturally. Added visited-position-signature tracking and a marker. Co-Authored-By: Claude Sonnet 5 Claude-Session: https://claude.ai/code/session_01YGSMkwjqiCk4XhbfN7ugD2 --- src/chess.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'src/chess.h') diff --git a/src/chess.h b/src/chess.h index 630f090..9b6303d 100755 --- a/src/chess.h +++ b/src/chess.h @@ -1652,6 +1652,18 @@ typedef struct _PIECE_DATA extern PIECE_DATA g_PieceData[8]; #define PIECE_VALUE_OVER_100(p) (g_PieceData[PIECE_TYPE(p)].uValueOver100) + +// _ScoreAllMoves / _ScoreQSearchMoves{InclChecks,NoChecks} (generate.c) bake +// a flat +120 move-ordering bias plus small MVV-LVA tie-break nudges into +// winning/even captures'/promotions' iValue -- harmless for sorting, but +// wrong once the value is used on the eval axis (compared against +// material-scale margins). Back it out to recover the pure SEE/ +// material-diff value. ComputeMoveScore() (searchsup.c) already does this; +// _ShouldWeConsiderThisMove() (search.c) reads iValue raw and needs it too. +#define MOVE_SCORE_ORDERING_BIAS(mv) \ + (PIECE_VALUE_OVER_100((mv).pCaptured) + 120 + \ + PIECE_VALUE_OVER_100((mv).pPromoted) - \ + PIECE_VALUE_OVER_100((mv).pMoved)) extern ULONG PieceValueOver100(PIECE p); -- cgit v1.3