From: Eelco de Groot <eelcogro@gmail.com>
Date: Mon, 16 Jun 2014 19:46:42 +0000 (+0200)
Subject: Don't special case for abs(beta) >= VALUE_MATE_IN_MAX_PLY
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=55a3e0af8d0d1e169cc8b16541ffeb41e157b66e

Don't special case for abs(beta) >= VALUE_MATE_IN_MAX_PLY

Remove from the search this special case and apply
null search and razoring also in mate positions.

Tested in no-regression mode and passed both

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 65431 W: 10860 L: 10810 D: 43761

and LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 34928 W: 4814 L: 4713 D: 25401

This patch kicks in only in mate positions and in
these cases it seems beneficial in finding mates
faster as Yery Spark measured on the Chest mate suite:

Total number of positions 6425
Fixed nodes 200K per position

master: 1049
new:    1154

And also the 5446 'hard' positions again with 2000K nodes
(those not found by both engines in 200K nodes):

master: 1069
new:    1395

bench: 7710548
---

diff --git a/src/search.cpp b/src/search.cpp
index e24d264d..acd042c0 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -566,7 +566,6 @@ namespace {
         &&  depth < 4 * ONE_PLY
         &&  eval + razor_margin(depth) <= alpha
         &&  ttMove == MOVE_NONE
-        &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
         && !pos.pawn_on_7th(pos.side_to_move()))
     {
         if (   depth <= ONE_PLY
@@ -594,7 +593,6 @@ namespace {
         && !ss->skipNullMove
         &&  depth >= 2 * ONE_PLY
         &&  eval >= beta
-        &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
         &&  pos.non_pawn_material(pos.side_to_move()))
     {
         ss->currentMove = MOVE_NULL;
@@ -604,7 +602,8 @@ namespace {
         // Null move dynamic reduction based on depth and value
         Depth R =  3 * ONE_PLY
                  + depth / 4
-                 + int(eval - beta) / PawnValueMg * ONE_PLY;
+                 + (abs(beta) < VALUE_KNOWN_WIN ? int(eval - beta) / PawnValueMg * ONE_PLY
+                                                : DEPTH_ZERO);
 
         pos.do_null_move(st);
         (ss+1)->skipNullMove = true;
@@ -619,7 +618,7 @@ namespace {
             if (nullValue >= VALUE_MATE_IN_MAX_PLY)
                 nullValue = beta;
 
-            if (depth < 12 * ONE_PLY)
+            if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
                 return nullValue;
 
             // Do verification search at high depths
@@ -699,6 +698,7 @@ moves_loop: // When in check and at SpNode search starts from here
     singularExtensionNode =   !RootNode
                            && !SpNode
                            &&  depth >= 8 * ONE_PLY
+                           &&  abs(beta) < VALUE_KNOWN_WIN
                            &&  ttMove != MOVE_NONE
                            && !excludedMove // Recursive singular search is not allowed
                            && (tte->bound() & BOUND_LOWER)
@@ -764,8 +764,7 @@ moves_loop: // When in check and at SpNode search starts from here
       if (    singularExtensionNode
           &&  move == ttMove
           && !ext
-          &&  pos.legal(move, ci.pinned)
-          &&  abs(ttValue) < VALUE_KNOWN_WIN)
+          &&  pos.legal(move, ci.pinned))
       {
           assert(ttValue != VALUE_NONE);