add improving heuristic

Results of bread_engine_1.5.5 vs bread_engine_1.5.4 (8+0.08, NULL, NULL, UHO_2024_8mvs_big_+115_+134.pgn):
Elo: 6.19 +/- 4.94, nElo: 8.52 +/- 6.80
LOS: 99.30 %, DrawRatio: 42.41 %, PairsRatio: 1.09
Games: 10040, Wins: 3578, Losses: 3399, Draws: 3063, Points: 5109.5 (50.89 %)
Ptnml(0-2): [379, 1002, 2129, 1081, 429], WL/DD Ratio: 3.34
LLR: 3.00 (102.0%) (-2.94, 2.94) [0.00, 8.00]

Author: Nonlinear2

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(bread_engine VERSION 1.5.4)
+project(bread_engine VERSION 1.5.5)
 
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED True)

dependencies/misc.hpp

@@ -113,6 +113,7 @@ struct Stack {
     Move excluded_move = Move::NO_MOVE;
     Move current_move = Move::NO_MOVE;
     Piece moved_piece = Piece::NONE;
+    int static_eval = NO_VALUE;
 };
 
 class KillerMoves {

src/core.cpp

@@ -359,6 +359,11 @@ int Engine::negamax(int depth, int alpha, int beta, Stack* ss){
     if (eval == NO_VALUE)
         eval = static_eval;
 
+    ss->static_eval = static_eval;
+
+    bool improving = is_valid(ss->static_eval) && is_valid((ss - 2)->static_eval) &&
+        ss->static_eval > (ss - 2)->static_eval;
+
     // pruning
     if (!pv && !in_check){
 
@@ -370,9 +375,8 @@ int Engine::negamax(int depth, int alpha, int beta, Stack* ss){
         }
 
         // reverse futility pruning
-        if (depth < 6 && eval - depth*150 - 281 >= beta){
+        if (depth < 6 && eval - depth*142 - 310 + 100*improving >= beta)
             return eval;
-        }
 
         // null move pruning
         // maybe check for zugzwang?