eval.c: defer B/N/R mobility scoring near enemy king, queen king-adjacency fix, FLIP() -> precomputed xColor

Bishop/knight/rook mobility computed during their own eval pass only
sees enemy pawn (B/N) or pawn+minor (R) attacks -- a square right next
to the enemy king looks "safe" and counts toward mobility even though
it plainly isn't (e.g. a pawn push cutting off a bishop's retreat onto
squares next to the enemy king). Below EVAL_MOBILITY_CAREFULLY_BELOW
(3) candidate squares, defer scoring to _EvalTrappedPieces, which
re-derives the true safe-escape count once every piece type -- the
enemy king included -- has contributed to the attack tables. Genuinely
0-mobility pieces are scored immediately instead: more attack info can
only shrink an already-empty set, so there's nothing to gain by
waiting.

Queen doesn't need deferral (its own eval pass runs after every
smaller piece type, so it already has complete information) -- instead
bbUnsafeForQueen now also excludes squares adjacent to the enemy king
unless we already defend them.

Also: precompute xColor = FLIP(uColor) once per function/loop
iteration everywhere eval.c could hit FLIP() more than once evaluating
it, instead of recomputing it at each use site.

Verified: precommit_check.sh (self-test + DEBUG smoke test) clean.
Curated ECM suites at sd10 vs head_reference: ecm_ringers 4/11 (was
3/11), ecm_confident_quick 70/90 (flat), ecm_hard_quick 19/90 (was
18/90) -- no regressions. Overnight self-play SPRT trending positive
(370 games, llr=+0.20).

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

1 files changed, 27 insertions, 10 deletions

diff --git a/src/chess.h b/src/chess.h
index 1dcb517..8d9a8d8 100755
--- a/src/chess.h
+++ b/src/chess.h
@@ -749,16 +749,33 @@ typedef struct _POSITION
 
     // temporary storage space for use in eval
     //
-    // Small fixed-capacity list of zero-mobility piece candidates per
-    // color (bishop/knight/rook/queen evals each can push one), not
-    // just the single most-recently-evaluated one -- a single COOR
-    // here used to silently let a later piece's candidacy overwrite an
-    // earlier one on the same side, discarding it even if it was a
-    // genuinely trapped (zero mobility + actually attacked) piece.
-    // Capacity of 4 is deliberately generous; if a position somehow
-    // has more than 4 simultaneously zero-mobility non-pawn pieces on
-    // one side, the rest are just dropped, not a real concern.
-    COOR cTrapped[2][4];
+    // Small fixed-capacity list of zero-mobility (or, for a deferred
+    // bishop/knight/rook -- see EVAL_MOBILITY_CAREFULLY_BELOW in
+    // eval.c -- low-mobility) piece candidates per color, not just the
+    // single most-recently-evaluated one -- a single COOR here used to
+    // silently let a later piece's candidacy overwrite an earlier one
+    // on the same side, discarding it even if it was a genuinely
+    // trapped (zero mobility + actually attacked) piece. Capacity of 6
+    // is deliberately generous; if a position somehow has more than 6
+    // simultaneously trapped-candidate non-pawn pieces on one side, the
+    // rest are just dropped, not a real concern.
+    //
+    // bbTrappedEscapes[side][u] is the nominating bishop/knight/rook's
+    // own bbMobility snapshot at nomination time, for a genuinely
+    // deferred candidate (see eval.c's _EvalBishop/_EvalKnight/
+    // _EvalRook) -- necessarily computed from incomplete attack-table
+    // information (the enemy king's, and for bishop/knight any
+    // not-yet-evaluated enemy slider's, attacks aren't known yet). Zero
+    // for every non-deferred candidate (queen, which never has this
+    // partial-information problem in the first place, or a
+    // bishop/knight/rook nominated at already-zero mobility -- nothing
+    // left to re-derive there, see eval.c's comment on why 0-mobility
+    // pieces are never deferred) -- _EvalTrappedPieces uses this being
+    // nonzero as the signal that a deferred re-check (and its own
+    // "mobility (deferred)" EVAL_TERM, skipped at nomination time) is
+    // owed to this candidate.
+    COOR cTrapped[2][6];
+    BITBOARD bbTrappedEscapes[2][6];
     ULONG uNumTrapped[2];
     ULONG uArmyScaler[2];
     ULONG uClosedScaler;