Retire cPawns/cNonPawns piece-location lists in favor of bbPawns/bbPieces/cKingSq, and hoist two redundant TotalNonPawnCount POPCNT calls out of per-node hot loops.

POSITION no longer stores cPawns[2][8], cNonPawns[2][16], uPawnCount[2],
uNonPawnCount[2][8], or uWhiteSqBishopCount[2] -- every reader now goes
through PawnMaterial/TotalNonPawnCount/WhiteSqBishopCount/KingPosition
(chess.h), computed from the already-incrementally-maintained bbPawns/
bbPieces/cKingSq bitboards via a single -mpopcnt POPCNT instead of a
stored counter. move.c's make/unmake loses the list-swap-on-removal
bookkeeping entirely. GNUmakefile now passes -mpopcnt so the popcount
builtins actually compile to one instruction instead of clang's ~15-op
SWAR fallback.

Measured a small but real nps regression from the naive swap (search.c's
QSearch move-filter and eval.c's _EvalKing were each recomputing the same
TotalNonPawnCount sum on every candidate move / twice per node); hoisted
both to a single call per node instead. Net result across a same-code
self-play match: ~1541.5 knps candidate vs ~1505.7 knps head_reference.

A third hoist (FindEnprisePiece out of SelectBestWithHistory) was tried
and reverted -- its cache isn't actually loop-invariant within a node
(populated from inside Eval(), which doesn't run before every selection
call), caught by a DEBUG-build ASSERT before it landed.

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

1 files changed, 23 insertions, 6 deletions

diff --git a/src/testmove.c b/src/testmove.c
index 6711046..9dbee96 100644
--- a/src/testmove.c
+++ b/src/testmove.c
@@ -46,16 +46,33 @@ Return value:
     ULONG w;
     COOR c;
     
-    if ((TRUE == v) && (pos->uPawnCount[u]))
+    if ((TRUE == v) && (pos->bbPawns[u]))
     {
-        w = rand() % pos->uPawnCount[u];
-        c = pos->cPawns[u][w];
+        BITBOARD bbPawns = pos->bbPawns[u];
+
+        w = rand() % FastCountBits(pos->bbPawns[u]);
+        do
+        {
+            c = CoorFromBitBoardRank8ToRank1(&bbPawns);
+            ASSERT(IS_ON_BOARD(c));
+        }
+        while (w-- > 0);
     }
     else
     {
-        ASSERT(pos->uNonPawnCount[u][0]);
-        w = rand() % pos->uNonPawnCount[u][0];
-        c = pos->cNonPawns[u][w];
+        COOR rgNonPawns[16];
+        ULONG uCount = 0;
+        BITBOARD bb = NON_KING_PIECES_BB(pos, u);
+        COOR cBit;
+
+        rgNonPawns[uCount++] = KingPosition(pos, u);
+        while (IS_ON_BOARD(cBit = CoorFromBitBoardRank8ToRank1(&bb)))
+        {
+            ASSERT(uCount < ARRAY_SIZE(rgNonPawns));
+            rgNonPawns[uCount++] = cBit;
+        }
+        w = rand() % uCount;
+        c = rgNonPawns[w];
     }
     ASSERT(IS_ON_BOARD(c));
     return(c);