From 19ff8e29026523e2d3c47f6542d564fe9cf537e6 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 16 Oct 2010 11:54:44 +0100
Subject: [PATCH] Pass evalMargin through SearchStack as eval

It has more sense to treat the two evaluation metrics
in the same way.

As a side effect now we use the correct eval margin when
pruning in a SplitPoint node.

No functional change in single thread.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---
 src/search.cpp | 23 ++++++++++++-----------
 src/search.h   |  1 +
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 64b8dd0e..1a63299e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -717,7 +717,7 @@ namespace {
     int64_t nodes;
     Move move;
     Depth depth, ext, newDepth;
-    Value value, evalMargin, alpha, beta;
+    Value value, alpha, beta;
     bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
     int researchCountFH, researchCountFL;
 
@@ -736,7 +736,8 @@ namespace {
 
     // Step 5. Evaluate the position statically
     // At root we do this only to get reference value for child nodes
-    ss->eval = isCheck ? VALUE_NONE : evaluate(pos, evalMargin);
+    ss->evalMargin = VALUE_NONE;
+    ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
 
     // Step 6. Razoring (omitted at root)
     // Step 7. Static null move pruning (omitted at root)
@@ -977,7 +978,7 @@ namespace {
     Key posKey;
     Move ttMove, move, excludedMove, threatMove;
     Depth ext, newDepth;
-    Value bestValue, value, evalMargin, oldAlpha;
+    Value bestValue, value, oldAlpha;
     Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
     bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
     bool mateThreat = false;
@@ -1050,19 +1051,19 @@ namespace {
     // Step 5. Evaluate the position statically and
     // update gain statistics of parent move.
     if (isCheck)
-        ss->eval = evalMargin = VALUE_NONE;
+        ss->eval = ss->evalMargin = VALUE_NONE;
     else if (tte)
     {
         assert(tte->static_value() != VALUE_NONE);
 
         ss->eval = tte->static_value();
-        evalMargin = tte->static_value_margin();
+        ss->evalMargin = tte->static_value_margin();
         refinedValue = refine_eval(tte, ss->eval, ply);
     }
     else
     {
-        refinedValue = ss->eval = evaluate(pos, evalMargin);
-        TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
+        refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
+        TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
     }
 
     // Save gain for the parent non-capture move
@@ -1187,8 +1188,8 @@ split_start:
     MovePicker& mp = SplitPoint ? *ss->sp->mp : mpBase;
     CheckInfo ci(pos);
     ss->bestMove = MOVE_NONE;
-    singleEvasion = SplitPoint ? false : isCheck && mp.number_of_evasions() == 1;
-    futilityBase = SplitPoint ? ss->eval : ss->eval + evalMargin;
+    singleEvasion = !SplitPoint && isCheck && mp.number_of_evasions() == 1;
+    futilityBase = ss->eval + ss->evalMargin;
     singularExtensionNode =  !SplitPoint
                            && depth >= SingularExtensionDepth[PvNode]
                            && tte
@@ -1429,7 +1430,7 @@ split_start:
 
     ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
     move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
-    TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, evalMargin);
+    TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
 
     // Update killers and history only for non capture moves that fails high
     if (    bestValue >= beta
@@ -2635,7 +2636,7 @@ split_start:
 
     // Initialize search stack
     init_ss_array(ss, PLY_MAX_PLUS_2);
-    ss[0].eval = VALUE_NONE;
+    ss[0].eval = ss[0].evalMargin = VALUE_NONE;
     count = 0;
 
     // Generate all legal moves
diff --git a/src/search.h b/src/search.h
index 5c635478..4bb8b0ad 100644
--- a/src/search.h
+++ b/src/search.h
@@ -57,6 +57,7 @@ struct SearchStack {
   Move killers[2];
   Depth reduction;
   Value eval;
+  Value evalMargin;
   bool skipNullMove;
   SplitPoint* sp;
 };
-- 
2.39.2