Increase nmp fixed reduction to 4 (#483)

Elo   | 3.09 +- 2.18 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 2.89 (-2.25, 2.89) [0.00, 3.00]
Games | N: 25994 W: 6399 L: 6168 D: 13427
Penta | [78, 3032, 6558, 3239, 90]

Elo   | 7.55 +- 3.62 (95%)
SPRT  | 40.0+0.40s Threads=1 Hash=64MB
LLR   | 2.89 (-2.25, 2.89) [0.00, 3.00]
Games | N: 8238 W: 1975 L: 1796 D: 4467
Penta | [2, 862, 2214, 1037, 4]

Bench: 7071570

src/search.cpp

@@ -521,7 +521,7 @@ int Negamax(int alpha, int beta, int depth, const bool cutNode, ThreadData* td,
             && BoardHasNonPawns(pos, pos->side)) {
 
             ss->move = NOMOVE;
-            const int R = 3 + depth / 3 + std::min((eval - beta) / 200, 3);
+            const int R = 4 + depth / 3 + std::min((eval - beta) / 200, 3);
             ss->contHistEntry = &sd->contHist[PieceTo(NOMOVE)];
 
             MakeNullMove(pos);

src/types.h

@@ -4,7 +4,7 @@
 // include the tune stuff here to give it global visibility
 #include "tune.h"
 
-#define NAME "Alexandria-7.1.0"
+#define NAME "Alexandria-7.1.1"
 
 inline int reductions[2][64][64];
 inline int lmp_margin[64][2];