From: Marco Costalba <mcostalba@gmail.com>
Date: Mon, 8 Dec 2014 08:46:21 +0000 (+0100)
Subject: Clarify when forcing the moves loop
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=589c711449ef09b459b76d8891b6abc5c0b843bd;hp=158864270a055fe20dca4a87f4b7a8aa9cedfeb9

Clarify when forcing the moves loop

In some cases we want to go direcly to the moves loop
without checking for early return. The patch make this
logic more clear and consistent.

Tested for no regression, passed STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 25282 W: 5136 L: 5022 D: 15124

and LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 72007 W: 12133 L: 12095 D: 47779

bench: 9316798
---

diff --git a/src/search.cpp b/src/search.cpp
index 7cf4a8a3..f15c572e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -514,7 +514,7 @@ namespace {
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
     ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
+    (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO;
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
 
     // Step 4. Transposition table lookup
@@ -599,6 +599,9 @@ namespace {
         TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
     }
 
+    if (ss->skipEarlyPruning)
+        goto moves_loop;
+
     if (   !pos.captured_piece_type()
         &&  ss->staticEval != VALUE_NONE
         && (ss-1)->staticEval != VALUE_NONE
@@ -629,7 +632,6 @@ namespace {
 
     // Step 7. Futility pruning: child node (skipped when in check)
     if (   !PvNode
-        && !ss->skipNullMove
         &&  depth < 7 * ONE_PLY
         &&  eval - futility_margin(depth) >= beta
         &&  eval < VALUE_KNOWN_WIN  // Do not return unproven wins
@@ -638,7 +640,6 @@ namespace {
 
     // Step 8. Null move search with verification search (is omitted in PV nodes)
     if (   !PvNode
-        && !ss->skipNullMove
         &&  depth >= 2 * ONE_PLY
         &&  eval >= beta
         &&  pos.non_pawn_material(pos.side_to_move()))
@@ -651,10 +652,10 @@ namespace {
         Depth R = (3 + depth / 4 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
 
         pos.do_null_move(st);
-        (ss+1)->skipNullMove = true;
+        (ss+1)->skipEarlyPruning = true;
         nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
                                       : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
-        (ss+1)->skipNullMove = false;
+        (ss+1)->skipEarlyPruning = false;
         pos.undo_null_move();
 
         if (nullValue >= beta)
@@ -667,10 +668,10 @@ namespace {
                 return nullValue;
 
             // Do verification search at high depths
-            ss->skipNullMove = true;
+            ss->skipEarlyPruning = true;
             Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
                                         :  search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
-            ss->skipNullMove = false;
+            ss->skipEarlyPruning = false;
 
             if (v >= beta)
                 return nullValue;
@@ -683,7 +684,6 @@ namespace {
     // prune the previous move.
     if (   !PvNode
         &&  depth >= 5 * ONE_PLY
-        && !ss->skipNullMove
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY)
     {
         Value rbeta = std::min(beta + 200, VALUE_INFINITE);
@@ -714,9 +714,9 @@ namespace {
         && (PvNode || ss->staticEval + 256 >= beta))
     {
         Depth d = 2 * (depth - 2 * ONE_PLY) - (PvNode ? DEPTH_ZERO : depth / 2);
-        ss->skipNullMove = true;
+        ss->skipEarlyPruning = true;
         search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d / 2, true);
-        ss->skipNullMove = false;
+        ss->skipEarlyPruning = false;
 
         tte = TT.probe(posKey);
         ttMove = tte ? tte->move() : MOVE_NONE;
@@ -816,9 +816,9 @@ moves_loop: // When in check and at SpNode search starts from here
       {
           Value rBeta = ttValue - 2 * depth / ONE_PLY;
           ss->excludedMove = move;
-          ss->skipNullMove = true;
+          ss->skipEarlyPruning = true;
           value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
-          ss->skipNullMove = false;
+          ss->skipEarlyPruning = false;
           ss->excludedMove = MOVE_NONE;
 
           if (value < rBeta)
diff --git a/src/search.h b/src/search.h
index 9151f840..20cfd474 100644
--- a/src/search.h
+++ b/src/search.h
@@ -46,7 +46,7 @@ struct Stack {
   Move killers[2];
   Depth reduction;
   Value staticEval;
-  bool skipNullMove;
+  bool skipEarlyPruning;
 };