From: Brian Sheppard <sheppardco@aol.com>
Date: Sat, 17 Jun 2017 02:27:36 +0000 (-0700)
Subject: Move depth calculation in probCut
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=f907d5b7d93a161bc88aeaec403631de9de092f9;ds=sidebyside

Move depth calculation in probCut

The change passed an STC regression:

LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 59350 W: 10793 L: 10738 D: 37819

I verified that there was no change in performance on my machine, but of course YMMV:

Results for 40 tests for each version:

                Base      Test      Diff
        Mean    2014338   2016121   -1783
        StDev   62655     63441     3860

p-value: 0.678
speedup: 0.001

No functional change.

Closes #1137
---

diff --git a/src/search.cpp b/src/search.cpp
index 8f3c4552..4f943b4c 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -784,9 +784,7 @@ namespace {
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY)
     {
         Value rbeta = std::min(beta + 200, VALUE_INFINITE);
-        Depth rdepth = depth - 4 * ONE_PLY;
 
-        assert(rdepth >= ONE_PLY);
         assert(is_ok((ss-1)->currentMove));
 
         MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
@@ -797,8 +795,9 @@ namespace {
                 ss->currentMove = move;
                 ss->history = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
 
+                assert(depth >= 5 * ONE_PLY);
                 pos.do_move(move, st);
-                value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
+                value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
                 pos.undo_move(move);
                 if (value >= rbeta)
                     return value;