From fd1460b2c135f6cef502fd167d1df0edf223e312 Mon Sep 17 00:00:00 2001
From: Scott Gasch <scott@gasch.org>
Date: Sun, 30 Aug 2026 17:17:44 -0700
Subject: Improving for nullmove, eval speedup, remove old cruft, bugfix in
 split / MP.

---
 src/search.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

(limited to 'src/search.c')

diff --git a/src/search.c b/src/search.c
index ab7d122..3879d9f 100755
--- a/src/search.c
+++ b/src/search.c
@@ -337,7 +337,12 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
     }
 
     // Maybe do nullmove pruning
-    iRoughEval = GetRoughEvalScore(ctx, iAlpha, iBeta, FALSE);
+    pi->iEval = iRoughEval = GetRoughEvalScore(ctx, iAlpha, iBeta, FALSE);
+    SCORE iImprovement = 0;
+    if (ctx->uPly > 1)
+    {
+        iImprovement = (iRoughEval - ctx->sPlyInfo[ctx->uPly - 2].iEval);
+    }
     GENERATE_NO_MOVES;
     if (!fSkipNull &&
         !fThreat &&
@@ -345,6 +350,7 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
                                    iAlpha,
                                    iBeta,
                                    iRoughEval,
+                                   iImprovement,
                                    uNextDepth))
     {
         if (TryNullmovePruning(ctx,
@@ -466,6 +472,7 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
                         ctx->sSearchFlags.fAvoidNullmove = TRUE;
                         RescoreMovesViaSearch(ctx, uDepth, iAlpha, iBeta);
                         ctx->sSearchFlags.fAvoidNullmove = FALSE;
+                        ASSERT(TRUE == pi->fMovesRescoredByIID);
                     }
                 }
 #endif
@@ -625,12 +632,13 @@ Search(IN SEARCHER_THREAD_CONTEXT *ctx,
         // underflow (ULONG) in that case, which is exactly why the
         // uDepth >= ONE_PLY check below short-circuits before the
         // g_fCanSplit[] indexing ever evaluates it.
-        if (((uLegalMoves >= 2)) &&
+        if (((uLegalMoves >= 3)) &&
             (0 != g_uNumHelpersAvailable) &&
+            (FALSE == pi->fMovesRescoredByIID) &&
             (0 == uFutilityMargin) &&
             (uDepth >= ONE_PLY) &&
             (TRUE == g_fCanSplit[uDepth / ONE_PLY - 1]) &&
-            (MOVE_COUNT(ctx, ctx->uPly) > 3))
+            (MOVE_COUNT(ctx, ctx->uPly) > 4))
         {
             ASSERT(pf->fAvoidNullmove == FALSE);
             ASSERT(uStage == TRY_GENERATED_MOVES);
-- 
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