From 25677ae2c6ea0e963720692ba10089f53cf39c0c Mon Sep 17 00:00:00 2001
From: Mattia Giambirtone <nocturn9x@nocturn9x.space>
Date: Sat, 11 May 2024 12:50:33 +0200
Subject: [PATCH] Add improved NMP reduction scheme (20.1 +/- 14)

---
 Chess/nimfish/nimfishpkg/search.nim | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/Chess/nimfish/nimfishpkg/search.nim b/Chess/nimfish/nimfishpkg/search.nim
index 13762f6..468f81e 100644
--- a/Chess/nimfish/nimfishpkg/search.nim
+++ b/Chess/nimfish/nimfishpkg/search.nim
@@ -56,7 +56,7 @@ const
     # Limit after which FP is disabled
     FP_DEPTH_LIMIT {.used.} = 1
     # Advantage threshold
-    FP_EVAL_MARGIN {.used.} = 300
+    FP_EVAL_MARGIN {.used.} = 125
 
     # Constants to configure LMP (Late
     # Move Pruning)
@@ -448,12 +448,7 @@ proc search(self: var SearchManager, depth, ply: int, alpha, beta: Score, isPV:
             self.board.makeNullMove()
             # We perform a shallower search because otherwise there would be no point in
             # doing NMP at all!
-            var reduction: int
-            when defined(NMP2):
-                # Reduce more based on depth
-                reduction = NMP_BASE_REDUCTION + depth div NMP_DEPTH_REDUCTION
-            else:
-                reduction = NMP_BASE_REDUCTION
+            var reduction = NMP_BASE_REDUCTION + depth div NMP_DEPTH_REDUCTION
             let score = -self.search(depth - reduction, ply + 1, -beta + 1, -beta, isPV=false)
             self.board.unmakeMove()
             if score >= beta: