Land bitboard move generation (Part A+B) and movesup.c bitboard queries; 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

1 files changed, 19 insertions, 1 deletions

diff --git a/src/testsup.c b/src/testsup.c
index 3ed50e3..d1b102d 100644
--- a/src/testsup.c
+++ b/src/testsup.c
@@ -87,7 +87,25 @@ GenerateRandomLegalPosition(POSITION *pos)
         {
             pos->cNonPawns[WHITE][u] = pos->cNonPawns[BLACK][u] = ILLEGAL_COOR;
         }
-        
+
+        // memset above zeroes cEpSquare to 0x00 (A8), a real on-board
+        // square, not the "no en passant" sentinel -- every random
+        // position generated by this function had a bogus "en passant
+        // available on a8" flag set regardless of whether that made
+        // any sense. Both the mailbox and bitboard pawn generators
+        // trust this field and will act on it (mailbox: any pawn whose
+        // normal diagonal-capture target happens to coincide with a8;
+        // bitboard: proactively, once per side per node, since
+        // _GenerateAllPawnMovesBB/_SaveMeAllPawnMovesBB gate their
+        // en-passant block on IS_ON_BOARD(cEpSquare) directly) --
+        // constructing a garbage "en passant capture" move whenever a
+        // pawn of the right color happens to sit on b7 by pure chance,
+        // which corrupts position state and was traced back to an
+        // intermittent TestSearch segfault (board_representation/
+        // MOVEGEN_MIGRATION.md section 6b).
+        pos->cEpSquare = ILLEGAL_COOR;
+
+
         //
         // Place both kings legally
         //