From: VoyagerOne <excelgeek@gmail.com>
Date: Sun, 14 Feb 2016 19:45:10 +0000 (+0000)
Subject: Fix futility pruning bug
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=744ed85a4dd3f478c4ce26e4257e64bf5c9abbdd

Fix futility pruning bug

PredictedDepth can be negative, causing the futility_margin to be negative.
It will be very difficult to tweak moveCount pruning and reduction formula, as they are tuned to prevent this behavior.

No functional change

Resolves #587
---

diff --git a/src/search.cpp b/src/search.cpp
index d61fca1b..f4c77847 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -969,7 +969,7 @@ moves_loop: // When in check search starts from here
               && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
               continue;
 
-          predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
+          predictedDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
 
           // Futility pruning: parent node
           if (predictedDepth < 7 * ONE_PLY)