From: Marco Costalba <mcostalba@gmail.com>
Date: Wed, 3 Jul 2013 16:58:49 +0000 (+0200)
Subject: Simplify aspiration window code
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=a55fb76dcc66c9cc17a81a9a99dd506108ee1fee;ds=sidebyside

Simplify aspiration window code

Here the main difference is that now we center
aspiration window on last returned score. This allows
to simplify handling of mate scores.

We have done a reversed SPRT tests, where we wanted to
verify if master is stronger than this patch.

Long TC: master vs this patch (reverse test)
LLR: -2.95 (-2.94,2.94)
Total: 37992 W: 7012 L: 6920 D: 24060

bench: 4507288
---

diff --git a/src/search.cpp b/src/search.cpp
index e1b7a1d7..15a9cde5 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();
@@ -328,17 +331,12 @@ 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;
+                alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
+                beta  = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
             }
 
             // Start with a small aspiration window and, in case of fail high/low,
@@ -366,35 +364,28 @@ namespace {
                 if (Signals.stop)
                     return;
 
-                // In case of failing high/low increase aspiration window and
+                // In case of failing low/high 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)
+                if (bestValue <= alpha)
                 {
-                    alpha = -VALUE_INFINITE;
-                    beta  =  VALUE_INFINITE;
+                    alpha = std::max(bestValue - delta, -VALUE_INFINITE);
+
+                    Signals.failedLowAtRoot = true;
+                    Signals.stopOnPonderhit = false;
                 }
                 else if (bestValue >= beta)
-                {
-                    beta += delta;
-                    delta += delta / 2;
-                }
+                    beta = std::min(bestValue + delta, VALUE_INFINITE);
+
                 else
-                {
-                    Signals.failedLowAtRoot = true;
-                    Signals.stopOnPonderhit = false;
+                    break;
 
-                    alpha -= delta;
-                    delta += delta / 2;
-                }
+                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