Move ONE_PLY to be 1 instead of 2: search()

Now that half-plies are no more used we can simplify
the code assuming that ONE_PLY is 1 and no more 2.

Verified with a SMP test:
LLR: 2.95 (-2.94,2.94) [-4.50,0.00]
Total: 8926 W: 1712 L: 1607 D: 5607

No functional change.

src/search.cpp

@@ -55,21 +55,20 @@ namespace {
   enum NodeType { Root, PV, NonPV };
 
   // Dynamic razoring margin based on depth
-  inline Value razor_margin(Depth d) { return Value(512 + 16 * d); }
+  inline Value razor_margin(Depth d) { return Value(512 + 32 * d); }
 
   // Futility lookup tables (initialized at startup) and their access functions
   int FutilityMoveCounts[2][32]; // [improving][depth]
 
   inline Value futility_margin(Depth d) {
-    return Value(100 * d);
+    return Value(200 * d);
   }
 
   // Reduction lookup tables (initialized at startup) and their access function
   int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
 
   template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
-
+    return (Depth) Reductions[PvNode][i][std::min(int(d), 63)][std::min(mn, 63)];
-    return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
   }
 
   size_t PVIdx;
@@ -127,21 +126,21 @@ void Search::init() {
   {
       double    pvRed = 0.00 + log(double(hd)) * log(double(mc)) / 3.00;
       double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
-      Reductions[1][1][hd][mc] = int8_t(   pvRed >= 1.0 ?    pvRed+0.5: 0)*int(ONE_PLY);
+      Reductions[1][1][hd][mc] = int8_t(   pvRed >= 1.0 ?    pvRed + 0.5: 0);
-      Reductions[0][1][hd][mc] = int8_t(nonPVRed >= 1.0 ? nonPVRed+0.5: 0)*int(ONE_PLY);
+      Reductions[0][1][hd][mc] = int8_t(nonPVRed >= 1.0 ? nonPVRed + 0.5: 0);
 
       Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
       Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
 
-      if (Reductions[0][0][hd][mc] >= 2 * ONE_PLY)
+      if (Reductions[0][0][hd][mc] >= 2)
-          Reductions[0][0][hd][mc] += ONE_PLY;
+          Reductions[0][0][hd][mc] += 1;
   }
 
   // Init futility move count array
   for (d = 0; d < 32; ++d)
   {
-      FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d + 0.00, 1.8));
+      FutilityMoveCounts[0][d] = int(2.4 + 0.222 * pow(d * 2 + 0.00, 1.8));
-      FutilityMoveCounts[1][d] = int(3.0 + 0.300 * pow(d + 0.98, 1.8));
+      FutilityMoveCounts[1][d] = int(3.0 + 0.300 * pow(d * 2 + 0.98, 1.8));
   }
 }
 
@@ -154,7 +153,7 @@ uint64_t Search::perft(Position& pos, Depth depth) {
   StateInfo st;
   uint64_t cnt, nodes = 0;
   CheckInfo ci(pos);
-  const bool leaf = depth == 2 * ONE_PLY;
+  const bool leaf = (depth == 2 * ONE_PLY);
 
   for (MoveList<LEGAL> it(pos); *it; ++it)
   {
@@ -561,8 +560,7 @@ namespace {
         assert(eval - beta >= 0);
 
         // Null move dynamic reduction based on depth and value
-        Depth R = (3 + (depth / 8 )) * ONE_PLY
+        Depth R = (3 + depth / 4 + std::min(int(eval - beta) / PawnValueMg, 3)) * ONE_PLY;
-                 + std::min(int(eval - beta) / PawnValueMg, 3) * ONE_PLY;
 
         pos.do_null_move(st);
         (ss+1)->skipNullMove = true;
@@ -627,10 +625,9 @@ namespace {
         && !ttMove
         && (PvNode || ss->staticEval + 256 >= beta))
     {
-        Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
+        Depth d = 2 * (depth - 2 * ONE_PLY) - (PvNode ? DEPTH_ZERO : depth / 2);
-        d = (d / 2) * 2;  // Round to nearest full-ply
         ss->skipNullMove = true;
-        search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d, true);
+        search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d / 2, true);
         ss->skipNullMove = false;
 
         tte = TT.probe(posKey);
@@ -696,7 +693,7 @@ moves_loop: // When in check and at SpNode search starts from here
           Signals.firstRootMove = (moveCount == 1);
 
           if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
-              sync_cout << "info depth " << depth / ONE_PLY
+              sync_cout << "info depth " << depth
                         << " currmove " << move_to_uci(move, pos.is_chess960())
                         << " currmovenumber " << moveCount + PVIdx << sync_endl;
       }
@@ -726,10 +723,10 @@ moves_loop: // When in check and at SpNode search starts from here
           && !ext
           &&  pos.legal(move, ci.pinned))
       {
-          Value rBeta = ttValue - int(depth);
+          Value rBeta = ttValue - int(2 * depth);
           ss->excludedMove = move;
           ss->skipNullMove = true;
-          value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, (depth / 4) * 2, cutNode);
+          value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
           ss->skipNullMove = false;
           ss->excludedMove = MOVE_NONE;
 
@@ -750,7 +747,7 @@ moves_loop: // When in check and at SpNode search starts from here
       {
           // Move count based pruning
           if (   depth < 16 * ONE_PLY
-              && moveCount >= FutilityMoveCounts[improving][depth] )
+              && moveCount >= FutilityMoveCounts[improving][depth])
           {
               if (SpNode)
                   splitPoint->mutex.lock();
@@ -1229,7 +1226,7 @@ moves_loop: // When in check and at SpNode search starts from here
 
     // Increase history value of the cut-off move and decrease all the other
     // played quiet moves.
-    Value bonus = Value(int(depth) * int(depth));
+    Value bonus = Value(4 * int(depth) * int(depth));
     History.update(pos.moved_piece(move), to_sq(move), bonus);
     for (int i = 0; i < quietsCnt; ++i)
     {

src/types.h

@@ -211,14 +211,14 @@ enum Piece {
 
 enum Depth {
 
-  ONE_PLY = 2,
+  ONE_PLY = 1,
 
-  DEPTH_ZERO          =  0 * ONE_PLY,
+  DEPTH_ZERO          =  0,
-  DEPTH_QS_CHECKS     =  0 * ONE_PLY,
+  DEPTH_QS_CHECKS     =  0,
-  DEPTH_QS_NO_CHECKS  = -1 * ONE_PLY,
+  DEPTH_QS_NO_CHECKS  = -1,
-  DEPTH_QS_RECAPTURES = -5 * ONE_PLY,
+  DEPTH_QS_RECAPTURES = -5,
 
-  DEPTH_NONE = -6 * ONE_PLY
+  DEPTH_NONE = -6
 };
 
 enum Square {