Add the LMR Deeper concept from Stockfish

AndyGrant · AndyGrant · commit 15f1e1224f14 · 2024-04-24T22:38:58.000-04:00
To the Stockfish developers, who read all of my commits, even though I seldom read theirs when it comes to Torch: This is already in Stockfish, and I've not shown any novel tweaks. You can disregard this commit for your Ethereal -> Fishtest pipeline. Elo | 2.66 +- 2.54 (95%) SPRT | 10.0+0.10s Threads=1 Hash=8MB LLR | 2.95 (-2.94, 2.94) [0.00, 3.00] Games | N: 34086 W: 8232 L: 7971 D: 17883 Penta | [171, 4006, 8457, 4209, 200] http://chess.grantnet.us/test/36419/ Elo | 2.31 +- 2.39 (95%) SPRT | 60.0+0.60s Threads=1 Hash=64MB LLR | 2.95 (-2.94, 2.94) [0.00, 3.00] Games | N: 36904 W: 8530 L: 8285 D: 20089 Penta | [35, 4156, 9826, 4399, 36] http://chess.grantnet.us/test/36422/ BENCH: 2,769,859
diff --git a/src/search.c b/src/search.c
@@ -719,8 +719,21 @@ int search(Thread *thread, PVariation *pv, int alpha, int beta, int depth, bool
             // Perform reduced depth search on a Null Window
             value = -search(thread, &lpv, -alpha-1, -alpha, newDepth-R, true);
 
+            if (value > alpha && R > 1) {
+
+                const int lmrDepth = newDepth - R;
+
+                newDepth += value > best + 35;
+                newDepth -= value < best + newDepth;
+
+                if (newDepth - 1 > lmrDepth)
+                    value = -search(thread, &lpv, -alpha-1, -alpha, newDepth-1, !cutnode);
+
+                doFullSearch = false;
+            }
+
             // Abandon searching here if we could not beat alpha
-            doFullSearch = value > alpha && R != 1;
+            else doFullSearch = value > alpha && R != 1;
         }
 
         else doFullSearch = !PvNode || played > 1;
diff --git a/src/uci.h b/src/uci.h
@@ -23,7 +23,7 @@
 
 #include "types.h"
 
-#define VERSION_ID "14.36"
+#define VERSION_ID "14.37"
 
 #ifndef LICENSE_OWNER
     #define LICENSE_OWNER "Unlicensed"
