From 6f079ae7203d56edca74722990c1f40db555de8a Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 30 Jun 2013 10:32:09 +0200
Subject: [PATCH] Simplify aspiration window loop

Don't open the window in case we find a mate score: this
will be takes care with next patch.

No functional change.
---
 src/search.cpp | 49 ++++++++++++++++++++-----------------------------
 1 file changed, 20 insertions(+), 29 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 15981755..4e0e8f9f 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -296,9 +296,12 @@ namespace {
     Value bestValue, alpha, beta, delta;
 
     memset(ss-1, 0, 4 * sizeof(Stack));
-    depth = BestMoveChanges = 0;
-    bestValue = delta = -VALUE_INFINITE;
     (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
+
+    depth = BestMoveChanges = 0;
+    bestValue = delta = alpha = -VALUE_INFINITE;
+    beta = VALUE_INFINITE;
+
     TT.new_search();
     History.clear();
     Gains.clear();
@@ -328,18 +331,13 @@ namespace {
         // MultiPV loop. We perform a full root search for each PV line
         for (PVIdx = 0; PVIdx < PVSize; PVIdx++)
         {
-            // Set aspiration window default width
-            if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
+            // Reset aspiration window starting size
+            if (depth >= 5)
             {
                 delta = Value(16);
                 alpha = RootMoves[PVIdx].prevScore - delta;
                 beta  = RootMoves[PVIdx].prevScore + delta;
             }
-            else
-            {
-                alpha = -VALUE_INFINITE;
-                beta  =  VALUE_INFINITE;
-            }
 
             // Start with a small aspiration window and, in case of fail high/low,
             // research with bigger window until not failing high/low anymore.
@@ -368,33 +366,26 @@ namespace {
 
                 // In case of failing high/low increase aspiration window and
                 // research, otherwise exit the loop.
-                if (bestValue > alpha && bestValue < beta)
-                    break;
-
-                // Give some update (without cluttering the UI) before to research
-                if (Time::now() - SearchTime > 3000)
-                    sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
-
-                if (abs(bestValue) >= VALUE_KNOWN_WIN)
-                {
-                    alpha = -VALUE_INFINITE;
-                    beta  =  VALUE_INFINITE;
-                }
-                else if (bestValue >= beta)
-                {
+                if (bestValue >= beta)
                     beta += delta;
-                    delta += delta / 2;
-                }
-                else
+
+                else if (bestValue <= alpha)
                 {
+                    alpha -= delta;
+
                     Signals.failedLowAtRoot = true;
                     Signals.stopOnPonderhit = false;
-
-                    alpha -= delta;
-                    delta += delta / 2;
                 }
+                else
+                    break;
+
+                delta += delta / 2;
 
                 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
+
+                // Give some update (without cluttering the UI) before to research
+                if (Time::now() - SearchTime > 3000)
+                    sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
             }
 
             // Sort the PV lines searched so far and update the GUI
-- 
2.39.2