Don't overwrite the TT Move on an upper bound

AndyGrant · AndyGrant · commit d9b9becc2558 · 2023-06-02T00:44:51.000-04:00
ELO   | 4.53 +- 3.14 (95%)
SPRT  | 10.0+0.10s Threads=1 Hash=8MB
LLR   | 2.96 (-2.94, 2.94) [0.00, 3.00]
GAMES | N: 23104 W: 5834 L: 5533 D: 11737

ELO   | 3.50 +- 2.61 (95%)
SPRT  | 60.0+0.60s Threads=1 Hash=64MB
LLR   | 2.97 (-2.94, 2.94) [0.00, 3.00]
GAMES | N: 32728 W: 8067 L: 7737 D: 16924

BENCH : 3,182,566
diff --git a/src/search.c b/src/search.c
@@ -784,8 +784,9 @@ int search(Thread *thread, PVariation *pv, int alpha, int beta, int depth, bool
     // the Root entry from the first line of play we examined. We also don't store into the
     // Transposition Table while attempting to veryify singularities
     if (!ns->excluded && (!RootNode || !thread->multiPV)) {
-        ttBound = best >= beta    ? BOUND_LOWER
-                : best > oldAlpha ? BOUND_EXACT : BOUND_UPPER;
+        ttBound  = best >= beta    ? BOUND_LOWER
+                 : best > oldAlpha ? BOUND_EXACT : BOUND_UPPER;
+        bestMove = ttBound == BOUND_UPPER ? NONE_MOVE : bestMove;
         tt_store(board->hash, thread->height, bestMove, best, eval, depth, ttBound);
     }
 
diff --git a/src/transposition.c b/src/transposition.c
@@ -154,12 +154,15 @@ void tt_store(uint64_t hash, int height, uint16_t move, int value, int eval, int
         && depth < replace->depth - 2)
         return;
 
+    // Don't overwrite a move if we don't have a new one
+    if (move || hash16 != replace->hash16)
+        replace->move = (uint16_t) move;
+
     // Finally, copy the new data into the replaced slot
     replace->depth      = (int8_t  ) depth;
     replace->generation = (uint8_t ) bound | Table.generation;
     replace->value      = (int16_t ) tt_value_to(value, height);
     replace->eval       = (int16_t ) eval;
-    replace->move       = (uint16_t) move;
     replace->hash16     = (uint16_t) hash16;
 }
 
diff --git a/src/uci.h b/src/uci.h
@@ -23,7 +23,7 @@
 
 #include "types.h"
 
-#define VERSION_ID "14.15"
+#define VERSION_ID "14.16"
 
 #ifndef LICENSE_OWNER
     #define LICENSE_OWNER "Unlicensed"
