From: H.G.Muller <hgm@hgm-xboard.(none)>
Date: Sun, 14 May 2017 13:19:38 +0000 (+0200)
Subject: Reduce null move less after first spite check
X-Git-Url: http://winboard.nl/cgi-bin?a=commitdiff_plain;h=bd2599842fde0aa1632c33f2ea4b63e8152817d0;p=crazywa.git

Reduce null move less after first spite check

The null-move reduction is aken one ply less after the first (check, evasion)
pair in a branch, to prevent spite checks pushing unavoidable mates over
the null-search horizon.
---

diff --git a/dropper.c b/dropper.c
index c8019d9..90fc7b2 100644
--- a/dropper.c
+++ b/dropper.c
@@ -1207,6 +1207,8 @@ if(hashMove && board[hashMove>>8&255] == 0) {char s[100];sprintf(s,"bad hash mov
  	}
     } else if(curEval >= beta && f.checker == CK_NONE) {
 	int nullDepth = depth - 3;
+	int eva = (ff->checker != CK_NONE) && !oldAna && nullDepth >= 0; // first evasion in branch, and depth of null-move search was higher before the check
+	nullDepth += eva; // reduce one less than normal after first evasion, to make sure we see same threats after spite check
 	if(nullDepth < 0) nullDepth = 0;
 	f.mutation = -2; // kludge to suppress testing for discovered check
 	f.newEval = f.pstEval;