From 2ce3570dc6aa67f82dd6f02fc4e518be3e33aabf Mon Sep 17 00:00:00 2001 From: Scott Gasch Date: Sat, 5 Sep 2026 00:19:59 -0700 Subject: Maintain pos->bbOccupied incrementally, dedupe its two from-scratch builders 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 Claude-Session: https://claude.ai/code/session_01P6g6iF6mD1Hau6nCZCzwYj --- src/move.c | 32 ++++++++++++++++++++++---------- 1 file changed, 22 insertions(+), 10 deletions(-) (limited to 'src/move.c') diff --git a/src/move.c b/src/move.c index 44e7073..27d86df 100755 --- a/src/move.c +++ b/src/move.c @@ -64,6 +64,8 @@ Return value: pos->cNonPawns[c][uIndex] = cTo; pos->bbPieces[c][PIECE_TYPE(p)] &= ~COOR_TO_BB(cFrom); pos->bbPieces[c][PIECE_TYPE(p)] |= COOR_TO_BB(cTo); + pos->bbOccupied &= ~COOR_TO_BB(cFrom); + pos->bbOccupied |= COOR_TO_BB(cTo); pos->u64NonPawnSig ^= g_u64SigSeeds[cFrom][PIECE_TYPE(p)][c]; pos->u64NonPawnSig ^= g_u64SigSeeds[cTo][PIECE_TYPE(p)][c]; #ifdef DEBUG @@ -123,6 +125,8 @@ Return value: pos->cPawns[c][uIndex] = cTo; pos->bbPawns[c] &= ~COOR_TO_BB(cFrom); pos->bbPawns[c] |= COOR_TO_BB(cTo); + pos->bbOccupied &= ~COOR_TO_BB(cFrom); + pos->bbOccupied |= COOR_TO_BB(cTo); pos->u64PawnSig ^= g_u64PawnSigSeeds[cFrom][c]; pos->u64PawnSig ^= g_u64PawnSigSeeds[cTo][c]; pos->rgSquare[cTo].pPiece = p; @@ -177,6 +181,8 @@ Return value: pos->cNonPawns[c][uIndex] = cTo; pos->bbPieces[c][PIECE_TYPE(p)] &= ~COOR_TO_BB(cFrom); pos->bbPieces[c][PIECE_TYPE(p)] |= COOR_TO_BB(cTo); + pos->bbOccupied &= ~COOR_TO_BB(cFrom); + pos->bbOccupied |= COOR_TO_BB(cTo); pos->rgSquare[cTo].pPiece = p; pos->rgSquare[cTo].uIndex = uIndex; #ifdef DEBUG @@ -185,7 +191,7 @@ Return value: } -void +void SlidePawnWithoutSigs(POSITION *pos, COOR cFrom, COOR cTo) /** @@ -228,6 +234,8 @@ Return value: pos->cPawns[c][uIndex] = cTo; pos->bbPawns[c] &= ~COOR_TO_BB(cFrom); pos->bbPawns[c] |= COOR_TO_BB(cTo); + pos->bbOccupied &= ~COOR_TO_BB(cFrom); + pos->bbOccupied |= COOR_TO_BB(cTo); pos->rgSquare[cTo].pPiece = p; pos->rgSquare[cTo].uIndex = uIndex; #ifdef DEBUG @@ -275,6 +283,7 @@ Return value: pos->rgSquare[cSquare].pPiece = EMPTY; ASSERT(IS_VALID_PIECE(pLifted)); ASSERT(!IS_KING(pLifted)); + pos->bbOccupied &= ~COOR_TO_BB(cSquare); uIndex = pos->rgSquare[cSquare].uIndex; #ifdef DEBUG ASSERT(IS_VALID_PIECE_INDEX(uIndex)); @@ -287,12 +296,12 @@ Return value: pos->iMaterialBalance[color] -= pv; pos->iMaterialBalance[FLIP(color)] += pv; ASSERT(pos->iMaterialBalance[WHITE] * -1 == pos->iMaterialBalance[BLACK]); - + if (IS_PAWN(pLifted)) { ASSERT(pos->cPawns[color][uIndex] == cSquare); ASSERT(pv == VALUE_PAWN); - + pos->uPawnMaterial[color] -= pv; ASSERT(pos->uPawnMaterial[color] <= (7 * VALUE_PAWN)); @@ -410,7 +419,8 @@ Return value: pos->rgSquare[cSquare].pPiece = EMPTY; ASSERT(IS_VALID_PIECE(pLifted)); ASSERT(!IS_KING(pLifted)); - + pos->bbOccupied &= ~COOR_TO_BB(cSquare); + uIndex = pos->rgSquare[cSquare].uIndex; #ifdef DEBUG ASSERT(IS_VALID_PIECE_INDEX(uIndex)); @@ -423,12 +433,12 @@ Return value: pos->iMaterialBalance[color] -= pv; pos->iMaterialBalance[FLIP(color)] += pv; ASSERT(pos->iMaterialBalance[WHITE] * -1 == pos->iMaterialBalance[BLACK]); - + if (IS_PAWN(pLifted)) { ASSERT(pos->cPawns[color][uIndex] == cSquare); ASSERT(pv == VALUE_PAWN); - + pos->uPawnMaterial[color] -= pv; ASSERT(pos->uPawnMaterial[color] <= (7 * VALUE_PAWN)); pos->bbPawns[color] &= ~COOR_TO_BB(cSquare); @@ -533,7 +543,8 @@ Return value: pos->iMaterialBalance[color] += pv; pos->iMaterialBalance[FLIP(color)] -= pv; ASSERT(pos->iMaterialBalance[WHITE] * -1 == pos->iMaterialBalance[BLACK]); - + pos->bbOccupied |= COOR_TO_BB(cSquare); + if (IS_PAWN(pPiece)) { // @@ -542,7 +553,7 @@ Return value: ASSERT(pv == VALUE_PAWN); pos->uPawnMaterial[color] += pv; ASSERT(pos->uPawnMaterial[color] <= (8 * VALUE_PAWN)); - + uIndex = pos->uPawnCount[color]; ASSERT((uIndex >= 0) && (uIndex <= 7)); pos->uPawnCount[color]++; @@ -626,7 +637,8 @@ Return value: pos->iMaterialBalance[color] += pv; pos->iMaterialBalance[FLIP(color)] -= pv; ASSERT(pos->iMaterialBalance[WHITE] * -1 == pos->iMaterialBalance[BLACK]); - + pos->bbOccupied |= COOR_TO_BB(cSquare); + if (IS_PAWN(pPiece)) { // @@ -635,7 +647,7 @@ Return value: ASSERT(pv == VALUE_PAWN); pos->uPawnMaterial[color] += pv; ASSERT(pos->uPawnMaterial[color] <= (8 * VALUE_PAWN)); - + uIndex = pos->uPawnCount[color]; ASSERT((uIndex >= 0) && (uIndex <= 7)); pos->uPawnCount[color]++; -- cgit v1.3