Remove PvNode dimension from Reductions array

This is a functional simplification: if we simply subtract one to Reductions[]
when PvNode is set, we can remove this dimension of the multidimensional array.
I think this saves about 8K of memory.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 10118 W: 2282 L: 2138 D: 5698
http://tests.stockfishchess.org/tests/view/5c6332b60ebc5925cffbdfed

LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 70765 W: 11617 L: 11575 D: 47573
http://tests.stockfishchess.org/tests/view/5c63379e0ebc5925cffbe0de

Closes https://github.com/official-stockfish/Stockfish/pull/2010

Bench 3261078

diff --git a/src/search.cpp b/src/search.cpp
index bbb6e5c445057a84e77efa0887d7073eb6bd96dd..dbfb94696ac3d60f92f2a0c22fcc52deb8b4f819 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -73,10 +73,10 @@ namespace {
 
   // Futility and reductions lookup tables, initialized at startup
   int FutilityMoveCounts[2][16]; // [improving][depth]
 
   // Futility and reductions lookup tables, initialized at startup
   int FutilityMoveCounts[2][16]; // [improving][depth]

-  int Reductions[2][2][64][64];  // [pv][improving][depth][moveNumber]
+  int Reductions[2][64][64];  // [improving][depth][moveNumber]

 
   template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
 
   template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {

-    return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
+    return (Reductions[i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] - PvNode) * ONE_PLY;

   }
 
   // History and stats update bonus, based on depth
   }
 
   // History and stats update bonus, based on depth


@@ -162,12 +162,11 @@ void Search::init() {
           {
               double r = log(d) * log(mc) / 1.95;
 
           {
               double r = log(d) * log(mc) / 1.95;
 

-              Reductions[NonPV][imp][d][mc] = int(std::round(r));
-              Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
+              Reductions[imp][d][mc] = std::round(r);

 
               // Increase reduction for non-PV nodes when eval is not improving
               if (!imp && r > 1.0)
 
               // Increase reduction for non-PV nodes when eval is not improving
               if (!imp && r > 1.0)

-                Reductions[NonPV][imp][d][mc]++;
+                Reductions[imp][d][mc]++;

           }
 
   for (int d = 0; d < 16; ++d)
           }
 
   for (int d = 0; d < 16; ++d)