Don't waste time copying the accum after a NULL move

Purely a speedup in practice.

ELO   | 2.30 +- 1.85 (95%)
SPRT  | 10.0+0.10s Threads=1 Hash=8MB
LLR   | 2.97 (-2.94, 2.94) [0.00, 3.00]
GAMES | N: 66512 W: 16514 L: 16074 D: 33924
http://chess.grantnet.us/test/31799/

NO FUNCTIONAL CHANGE

BENCH : 3,349,466

Author: AndyGrant

src/move.c

@@ -379,8 +379,6 @@ void applyNullMove(Board *board, Undo *undo) {
     }
 
     board->threats = allAttackedSquares(board, !board->turn);
-
-    nnue_push(board);
 }
 
 
@@ -412,6 +410,9 @@ void revertMove(Board *board, uint16_t move, Undo *undo) {
     board->numMoves--;
     board->fullMoveCounter--;
 
+    // Update Accumulator pointer
+    nnue_pop(board);
+
     if (MoveType(move) == NORMAL_MOVE) {
 
         const int fromType = pieceType(board->squares[to]);

src/nnue/accumulator.c

@@ -132,13 +132,6 @@ void nnue_update_accumulator(NNUEAccumulator *accum, Board *board, int colour, i
     if (!(accum-1)->accurate[colour])
         nnue_update_accumulator((accum-1), board, colour, relksq);
 
-    // The last move was a NULL move so we can cheat and copy
-    if (!accum->changes) {
-        memcpy(&accum->values[colour], &(accum-1)->values[colour], sizeof(int16_t) * KPSIZE);
-        accum->accurate[colour] = TRUE;
-        return;
-    }
-
     // Determine the features that have changed, by looping through them
     for (NNUEDelta *x = &accum->deltas[0]; x < &accum->deltas[0] + accum->changes; x++) {
 

src/nnue/accumulator.h

@@ -35,19 +35,22 @@ INLINE void nnue_delete_accumulators(NNUEAccumulator* ptr) {
     align_free(ptr);
 }
 
+INLINE void nnue_pop(Board *board) {
+    if (USE_NNUE && board->thread != NULL)
+        --board->thread->nnuePointer;
+}
+
 INLINE void nnue_push(Board *board) {
     if (USE_NNUE && board->thread != NULL) {
-        const int height = board->thread->height;
-        NNUEAccumulator *accum = &board->thread->nnueStack[height+1];
+        NNUEAccumulator *accum = ++board->thread->nnuePointer;
         accum->accurate[WHITE] = accum->accurate[BLACK] = FALSE;
         accum->changes = 0;
     }
 }
 
 INLINE void nnue_move_piece(Board *board, int piece, int from, int to) {
     if (USE_NNUE && board->thread != NULL) {
-        const int height = board->thread->height;
-        NNUEAccumulator *accum = &board->thread->nnueStack[height+1];
+        NNUEAccumulator *accum = board->thread->nnuePointer;
         accum->deltas[accum->changes++] = (NNUEDelta) { piece, from, to };
     }
 }

src/nnue/nnue.c

@@ -481,7 +481,7 @@ int nnue_evaluate(Thread *thread, Board *board) {
     ALIGN64 float outN1[L1SIZE];
     ALIGN64 float outN2[L1SIZE];
 
-    NNUEAccumulator *accum = &thread->nnueStack[thread->height];
+    NNUEAccumulator *accum = thread->nnuePointer;
 
     if (!accum->accurate[WHITE]) {
 

src/thread.c

@@ -102,6 +102,7 @@ void newSearchThreadPool(Thread *threads, Board *board, Limits *limits, TimeMana
 
         threads[i].nnueStack[0].accurate[WHITE] = 0;
         threads[i].nnueStack[0].accurate[BLACK] = 0;
+        threads[i].nnuePointer = &threads[i].nnueStack[0];
 
         memset(threads[i].nodeStates, 0, sizeof(NodeState) * STACK_SIZE);
     }

src/thread.h

@@ -65,7 +65,7 @@ struct Thread {
     int depth, seldepth, height, completed;
 
     NodeState *states, nodeStates[STACK_SIZE];
-    NNUEAccumulator *nnueStack;
+    NNUEAccumulator *nnueStack, *nnuePointer;
     Undo undoStack[STACK_SIZE];
 
     ALIGN64 PKTable pktable;

src/uci.h

@@ -22,7 +22,7 @@
 
 #include "types.h"
 
-#define VERSION_ID "14.08"
+#define VERSION_ID "14.09"
 
 #ifndef LICENSE_OWNER
     #define LICENSE_OWNER "Unlicensed"