From ba803fe406ee2470aa461578f530d292380ec241 Mon Sep 17 00:00:00 2001
From: Scott Gasch <scott@gasch.org>
Date: Tue, 25 Aug 2026 14:03:46 -0700
Subject: Add LMR with PV-adjacency guard (v7), verified against saved binary

Late Move Reductions using a depth x movecount table (Ethereal-style
formula), gated off PV nodes and the ply directly below a PV node
(PLY_INFO.fIsPVNode), with magnitude-aware re-search on fail-high.
Verified node-for-node identical to the previously tested-good v7
binary on a canary position (sd 10) after reconstructing from a ZFS
snapshot of search.c/root.c/split.c taken just before that binary was
built.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
---
 src/chess.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'src/chess.h')

diff --git a/src/chess.h b/src/chess.h
index 245a3b0..abf802e 100755
--- a/src/chess.h
+++ b/src/chess.h
@@ -819,6 +819,10 @@ typedef struct _COUNTERS
         UINT64 u64LazyEvals;
         UINT64 u64FullEvals;
         UINT64 u64CyclesInEval;
+        UINT64 u64HistoryPrunes;
+        UINT64 u64HistoryPruneReSearches;
+        UINT64 u64FutilityCandidates;
+        UINT64 u64FutilityPrunes;
     }
     tree;
 
@@ -928,6 +932,7 @@ typedef struct _PLY_INFO
 #endif
     SCORE iEval;
     INT iExtensionAmount;
+    FLAG fIsPVNode;                           // (iBeta != iAlpha+1) at this ply
     FLAG fInCheck;
     FLAG fInQsearch;
     MOVE mv;
@@ -2315,6 +2320,14 @@ ComputeMoveScore(IN SEARCHER_THREAD_CONTEXT *ctx,
 FLAG
 ThreadUnderTerminatingSplit(SEARCHER_THREAD_CONTEXT *);
 
+void
+InitializeLMRTable(void);
+
+INT
+ExtraReduction(IN ULONG uRemainingDepth,
+              IN ULONG uMoveNum,
+              IN ULONG uFailHighPct);
+
 FLAG
 WeShouldDoHistoryPruning(IN SCORE iRoughEval,
                          IN SCORE iAlpha,
-- 
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