Merge Joona's new aspiration window search

It seems very positive.

After 999 games at 1'+0" result is: +249 -216 =534 +11 ELO

And after another 456 games we still have: +122 -113 =221

src/search.cpp

@@ -47,6 +47,26 @@ namespace {
 
   /// Types
 
+  // IterationInfoType stores search results for each iteration
+  //
+  // Because we use relatively small (dynamic) aspiration window,
+  // there happens many fail highs and fail lows in root. And
+  // because we don't do researches in those cases, "value" stored
+  // here is not necessarily exact. Instead in case of fail high/low
+  // we guess what the right value might be and store our guess
+  // as a "speculated value" and then move on. Speculated values are
+  // used just to calculate aspiration window width, so also if are
+  // not exact is not big a problem.
+
+  struct IterationInfoType {
+
+    IterationInfoType(Value v = Value(0), Value sv = Value(0))
+    : value(v), speculatedValue(sv) {}
+
+    Value value, speculatedValue;
+  };
+
+
   // The BetaCounterType class is used to order moves at ply one.
   // Apart for the first one that has its score, following moves
   // normally have score -VALUE_INFINITE, so are ordered according
@@ -196,7 +216,7 @@ namespace {
   BetaCounterType BetaCounter;
 
   // Scores and number of times the best move changed for each iteration:
-  Value ValueByIteration[PLY_MAX_PLUS_2];
+  IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
   int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
 
   // MultiPV mode
@@ -214,6 +234,7 @@ namespace {
   bool AbortSearch;
   bool Quit;
   bool FailHigh;
+  bool FailLow;
   bool Problem;
   bool PonderingEnabled;
   int ExactMaxTime;
@@ -246,13 +267,10 @@ namespace {
   /// Functions
 
   Value id_loop(const Position &pos, Move searchMoves[]);
-  Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
+  Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta);
-  Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
+  Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
-                  Depth depth, int ply, int threadID);
+  Value search(Position &pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
-  Value search(Position &pos, SearchStack ss[], Value beta,
+  Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
-               Depth depth, int ply, bool allowNullmove, int threadID);
-  Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
-                Depth depth, int ply, int threadID);
   void sp_search(SplitPoint *sp, int threadID);
   void sp_search_pv(SplitPoint *sp, int threadID);
   void init_node(SearchStack ss[], int ply, int threadID);
@@ -380,6 +398,7 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   AbortSearch = false;
   Quit = false;
   FailHigh = false;
+  FailLow = false;
   Problem = false;
   ExactMaxTime = maxTime;
 
@@ -654,14 +673,13 @@ namespace {
         ss[i].init(i);
         ss[i].initKillers();
     }
-    ValueByIteration[0] = Value(0);
+    IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
-    ValueByIteration[1] = rml.get_move_score(0);
     Iteration = 1;
 
     EasyMove = rml.scan_for_easy_move();
 
     // Iterative deepening loop
-    while (!AbortSearch && Iteration < PLY_MAX)
+    while (Iteration < PLY_MAX)
     {
         // Initialize iteration
         rml.sort();
@@ -672,8 +690,62 @@ namespace {
 
         std::cout << "info depth " << Iteration << std::endl;
 
+        // Calculate dynamic search window based on previous iterations
+        Value alpha, beta;
+
+        if (MultiPV == 1 && Iteration >= 6)
+        {
+            int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
+            int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
+
+            int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
+
+            alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
+            beta  = Min(IterationInfo[Iteration - 1].value + delta,  VALUE_INFINITE);
+        }
+        else
+        {
+            alpha = - VALUE_INFINITE;
+            beta  =   VALUE_INFINITE;
+        }
+
         // Search to the current depth
-        ValueByIteration[Iteration] = root_search(p, ss, rml);
+        Value value = root_search(p, ss, rml, alpha, beta);
+
+        // Write PV to transposition table, in case the relevant entries have
+        // been overwritten during the search.
+        TT.insert_pv(p, ss[0].pv);
+
+        if (AbortSearch)
+            break; // Value cannot be trusted. Break out immediately!
+
+        //Save info about search result
+        Value speculatedValue;
+        bool fHigh = false;
+        bool fLow = false;
+        Value delta = value - IterationInfo[Iteration - 1].value;
+
+        if (value >= beta)
+        {
+            assert(delta > 0);
+
+            fHigh = true;
+            speculatedValue = value + delta;
+            BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
+        }
+        else if (value <= alpha)
+        {
+            assert(value == alpha);
+            assert(delta < 0);
+
+            fLow = true;
+            speculatedValue = value + delta;
+            BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
+        } else
+            speculatedValue = value;
+
+        speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
+        IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
 
         // Erase the easy move if it differs from the new best move
         if (ss[0].pv[0] != EasyMove)
@@ -692,13 +764,15 @@ namespace {
 
             // Stop search early when the last two iterations returned a mate score
             if (  Iteration >= 6
-                && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
+                && abs(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
-                && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
+                && abs(IterationInfo[Iteration-1].value) >= abs(VALUE_MATE) - 100)
                 stopSearch = true;
 
             // Stop search early if one move seems to be much better than the rest
             int64_t nodes = nodes_searched();
             if (   Iteration >= 8
+                && !fLow
+                && !fHigh
                 && EasyMove == ss[0].pv[0]
                 && (  (   rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
                        && current_search_time() > MaxSearchTime / 16)
@@ -719,15 +793,13 @@ namespace {
 
             if (stopSearch)
             {
+                //FIXME: Implement fail-low emergency measures
                 if (!PonderSearch)
                     break;
                 else
                     StopOnPonderhit = true;
             }
         }
-        // Write PV to transposition table, in case the relevant entries have
-        // been overwritten during the search:
-        TT.insert_pv(p, ss[0].pv);
 
         if (MaxDepth && Iteration >= MaxDepth)
             break;
@@ -784,15 +856,23 @@ namespace {
   // scheme (perhaps we should try to use this at internal PV nodes, too?)
   // and prints some information to the standard output.
 
-  Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
+  Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
 
-    Value alpha = -VALUE_INFINITE;
+    Value oldAlpha = alpha;
-    Value beta = VALUE_INFINITE, value;
+    Value value;
     Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
 
     // Loop through all the moves in the root move list
     for (int i = 0; i <  rml.move_count() && !AbortSearch; i++)
     {
+        if (alpha >= beta)
+        {
+            // We failed high, invalidate and skip next moves, leave node-counters
+            // and beta-counters as they are and quickly return, we will try to do
+            // a research at the next iteration with a bigger aspiration window.
+            rml.set_move_score(i, -VALUE_INFINITE);
+            continue;
+        }
         int64_t nodes;
         Move move;
         StateInfo st;
@@ -825,12 +905,12 @@ namespace {
 
         if (i < MultiPV)
         {
-            value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
+            value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
             // If the value has dropped a lot compared to the last iteration,
             // set the boolean variable Problem to true. This variable is used
             // for time managment: When Problem is true, we try to complete the
             // current iteration before playing a move.
-            Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
+            Problem = (Iteration >= 2 && value <= IterationInfo[Iteration-1].value - ProblemMargin);
 
             if (Problem && StopOnPonderhit)
                 StopOnPonderhit = false;
@@ -855,7 +935,7 @@ namespace {
         // was aborted because the user interrupted the search or because we
         // ran out of time. In this case, the return value of the search cannot
         // be trusted, and we break out of the loop without updating the best
-        // move and/or PV:
+        // move and/or PV.
         if (AbortSearch)
             break;
 
@@ -874,7 +954,7 @@ namespace {
             rml.set_move_score(i, -VALUE_INFINITE);
         else
         {
-            // New best move!
+            // PV move or new best move!
 
             // Update PV
             rml.set_move_score(i, value);
@@ -906,11 +986,12 @@ namespace {
                     LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
                             << std::endl;
 
+                if (value > alpha)
                     alpha = value;
 
                 // Reset the global variable Problem to false if the value isn't too
                 // far below the final value from the last iteration.
-                if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
+                if (value > IterationInfo[Iteration - 1].value - NoProblemMargin)
                     Problem = false;
             }
             else // MultiPV > 1
@@ -934,7 +1015,11 @@ namespace {
                 }
                 alpha = rml.get_move_score(Min(i, MultiPV-1));
             }
-        }
+        } // New best move case
+
+        assert(alpha >= oldAlpha);
+
+        FailLow = (alpha == oldAlpha);
     }
     return alpha;
   }
@@ -1083,7 +1168,7 @@ namespace {
           // (from the computer's point of view) since the previous iteration:
           if (   ply == 1
               && Iteration >= 2
-              && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
+              && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
               Problem = true;
       }
 
@@ -1796,7 +1881,7 @@ namespace {
         // (from the computer's point of view) since the previous iteration.
         if (   sp->ply == 1
             && Iteration >= 2
-            && -value <= ValueByIteration[Iteration-1] - ProblemMargin)
+            && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
             Problem = true;
       }
       lock_release(&(sp->lock));
@@ -2425,8 +2510,8 @@ namespace {
         return;
 
     bool overTime =     t > AbsoluteMaxSearchTime
-                     || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime)
+                     || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
-                     || (  !FailHigh && !fail_high_ply_1() && !Problem
+                     || (  !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
                          && t > 6*(MaxSearchTime + ExtraSearchTime));
 
     if (   (Iteration >= 3 && (!InfiniteSearch && overTime))
@@ -2447,8 +2532,8 @@ namespace {
        (!InfiniteSearch && (StopOnPonderhit ||
                             t > AbsoluteMaxSearchTime ||
                             (RootMoveNumber == 1 &&
-                             t > MaxSearchTime + ExtraSearchTime) ||
+                             t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
-                            (!FailHigh && !fail_high_ply_1() && !Problem &&
+                            (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
                              t > 6*(MaxSearchTime + ExtraSearchTime)))))
       AbortSearch = true;
   }