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chess.h: add POSITION::bbOccupied (full-board occupancy, both colors,
every piece including kings), maintained incrementally alongside
bbPieces/bbPawns rather than rebuilt on demand -- resolves the open
question in EVAL.md section 0 about whether this is worth doing given
both generate.c and the planned eval.c mobility rewrite need it.
move.c: SlidePiece/SlidePawn/LiftPiece/PlacePiece and their
WithoutSigs variants now maintain bbOccupied at the same choke points
that already maintain bbPieces/bbPawns -- unconditionally, since
occupancy doesn't care about piece type or color. Kings only ever
move through SlidePiece/SlidePieceWithoutSigs (never Lift/Place), so
no separate king-specific update site was needed.
fen.c: populate bbOccupied when parsing a FEN.
board.c: VerifyPositionConsistency cross-checks pos->bbOccupied
against a from-scratch rebuild, same pattern already used for
bbPieces/bbPawns.
generate.c/movesup.c/see.c: replace call sites that rebuilt full
occupancy via _BuildFullOccupiedBB/_BuildOccupiedBB with direct reads
of pos->bbOccupied; delete see.c's _BuildOccupiedBB, which was a
byte-for-byte duplicate of generate.c's _BuildFullOccupiedBB (kept
only as the from-scratch ground truth for the new consistency check
and testgenerate.c's benchmark harness).
testsup.c: GenerateRandomLegalPosition builds POSITIONs by poking
rgSquare/bbPieces/bbPawns directly, bypassing both move.c and fen.c --
a third construction path the above missed. It never set bbOccupied,
so the new VerifyPositionConsistency check failed on every generated
position, and since generation retries until a position verifies, the
self-test suite spun forever (100% CPU, no progress) instead of
crashing outright. Fixed by setting bbOccupied at all four placement
sites (both kings, pawn, non-pawn piece). Full self-test suite and
precommit_check.sh verified clean afterward.
board_representation/EVAL.md: record the bbOccupied decision and
rationale, resolving section 0's open question.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01P6g6iF6mD1Hau6nCZCzwYj
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default on
Implements the full board_representation/MOVEGEN_MIGRATION.md scope:
bitboard-backed generators for all six not-in-check piece types plus
the JumpTable-avoiding whole-node dispatch fork (_GenerateAllMovesBB),
the in-check escape path (king flight + block/capture), and
movesup.c's ExposesCheck/FasterExposesCheck/ExposesCheckEp/IsAttacked/
InCheck bitboard equivalents. Nine toggles total
(GENERATE_{KNIGHT,KING,ROOK,BISHOP,QUEEN,PAWN}_BITBOARD,
GENERATE_ESCAPES_{KING,BLOCK}_BITBOARD, EXPOSESCHECK_BITBOARD,
ISATTACKED_BITBOARD), all now on by default in GNUmakefile --
DISABLE_BITBOARD_MOVEGEN=1 opts back into the mailbox path, which
remains fully present and compiled either way.
Correctness verified via perft (Kiwipete, Position 4), the move-set
comparison harness across 20,000 random positions, all nine toggles
combined cleanly (15/15 runs, after fixing a GenerateRandomLegalPosition
en-passant-sentinel bug in the test harness), and sd10 on all three
curated suites showing zero solve-count regression vs head_reference
(the ecm_hard_quick delta traced to unrelated intervening commits).
Speed: most individual generators land near parity by design (mailbox's
per-square walk was already close to O(destination count)); the real,
consistent wins are the dispatch-layer fork (up to 23% in dense
positions) and IsAttackedBB (0.73x-0.93x of mailbox).
Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AbHkVrm5KUyzLwWd3GHmo6
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countermove promotion, retired hung-piece-escape and NumLeftoverMovesToSelect.
Full session was built on a "measure the pick, not the game" methodology:
aggregate solve counts on curated suites are too noisy to tune move-ordering
knobs against, so most decisions here came from per-move fail-high/alpha-raise
rates at much larger sample sizes (leftover FH% instrumentation, a zero-
selection-budget diagnostic that isolates a single best-of-remaining pick,
and evidence-bucket calibration), not solve-count deltas alone. See
CLAUDE.md's "Dynamic move ordering experiments" section for the reusable
methodology and generate.c's _ScoreAllMoves comment for the resulting
ordering hierarchy.
Changes:
- Added g_ContinuationHistory: same growth/decay math as the existing
g_HistoryCounters butterfly table, additionally keyed by the previous
move, so its magnitude is self-calibrated rather than a hand-picked
constant. Flat, sufficient response across a 256x scale sweep.
- Countermove-table matches now get a real GOOD_MOVE-tier promotion
(previously the table was write-only, tracked for stats but never read
for ordering), but only when the match's own accumulated
history+continuation evidence clears COUNTERMOVE_EVIDENCE_THRESHOLD
(10,000) -- a raw match with no track record was shown to perform
identically to an ordinary leftover (~0.6-0.85% FH), so promoting on
match alone would have repeated hung-piece-escape's mistake below.
- Retired hung-piece-escape's unconditional GOOD_MOVE-tier promotion.
Evidence-calibration showed the overwhelming majority of triggers (a
zero-evidence population 250-1000x larger than countermove's) performed
at the plain-leftover baseline -- the promotion was mostly free tier-
escape treatment for moves that hadn't earned it. Replaced with
FLEE_BONUS, a flat same-tier nudge inside SelectBestWithHistory (never
escapes GOOD_MOVE/leftover classification, unlike a generation-time
promotion) at the magnitude found to plateau a same-tier-nudge sweep.
- Retired NumLeftoverMovesToSelect (the depth-indexed budget on how many
leftover moves got a full selection scan before falling back to
unsorted order). search.c's main move loop now always fully selects --
the leftover pool was shown to contain real, findable signal a bailout
budget was discarding for a node-count savings that didn't hold up net-
net once measured by solve counts and fail-high rates rather than raw
node counts (noisy on small suites independent of this change).
- Collapsed leftover-move instrumentation from sorted/raw pairs down to a
single set now that "raw" (unsorted fallback) is structurally
impossible; kept the countermove evidence-bucket calibration counters
(ongoing check that COUNTERMOVE_EVIDENCE_THRESHOLD stays well-
calibrated); removed the contested-node A/B harness and hung-piece
evidence calibration now that the decisions they were built to inform
are made.
Net effect on the three curated suites (sd 10): solve counts wash (tied,
+1, -1 across ringers/confident/hard), leftover fail-high rate improved
consistently on all three (the intended, directly-measured target of this
work). Not yet validated beyond sd 10 -- an sn-based run or
eval_tune/match_play.py head-to-head gate is the natural next check before
leaning on this as a proven strength gain rather than a directionally-
sound, sd-10-clean change.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_014XePz6Sk4qQsTaP2jVJWJu
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of iValue; harden against a latent ComputeMoveExtension bug.
DO_IID's "is the top move crappy" gate compared raw iValue against
SORT_THESE_FIRST only, missing that ordinary killer moves (FIRST_KILLER
through FOURTH_KILLER) sit below that threshold too -- a killer that
already proved itself elsewhere in the tree was being treated as
"crappy" and triggering an unnecessary shallow rescore. Fixed by also
excluding killer-flagged moves from the gate.
RescoreMovesViaSearch corrupted the winning move's real search score by
OR-ing in SORT_THESE_FIRST to force it to sort first (`mvf[uBest].iValue
|= SORT_THESE_FIRST`) -- unnecessary (SelectBest{With,No}History already
find the true max by plain magnitude comparison, no flag needed) and
actively dangerous: a later ComputeMoveScore() call on that same move,
if it's a capture, would see the corrupted value, mistake it for
generate.c's biased-capture-ordering format, and subtract the wrong
bias entirely. Removed the OR; added an explicit
PLY_INFO.fMovesRescoredByIID flag so ComputeMoveScore and the main
search-loop's move-selection call can both recognize "this ply's
iValue holds a real eval-axis score" without relying on bit-pattern
inference.
Consequently, ComputeMoveScore now trusts an IID-rescored move's score
outright instead of running it through the capture-bias-subtraction or
quiet-move-collapse-to-0 logic (both of which assume generate.c's
ordering encoding, which a rescored ply no longer holds). Separately
hardened it against quiet killer-mate moves, which can reach
SORT_THESE_FIRST via a different, capture-unrelated path and were
incorrectly getting the capture bias subtracted from them; they now
correctly collapse to 0 like other quiet moves.
Two follow-on ideas -- blending history into the real IID score (scaled
or capped) and a exact-tie-only history tiebreak -- were implemented,
measured, and rejected: blending invents a new, leak-prone move-scoring
axis for no measured benefit, and the tiebreak-only compromise still
cost solves relative to just trusting the real score outright. Main
search's move-selection call now branches once per selection (not once
per candidate move) between SelectBestNoHistory (IID-rescored plies)
and SelectBestWithHistory (everyone else), keeping the overwhelmingly
common non-rescored path at zero added cost.
Net measured effect (ecm_ringers.ep_/ecm_confident_quick.ep_/
ecm_hard_quick.ep_, sn=5M): 10/90/9, down from a pre-existing 11/88/10
on ringers and hard specifically -- see lmr_testing/RESULTS.md for the
full sweep of rejected alternatives and why the regression was accepted
as the cost of removing a latent, leak-prone bug class rather than
chasing the exact prior numbers.
Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YGSMkwjqiCk4XhbfN7ugD2
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