Permalink
Browse files

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
  • Loading branch information...
2 parents e7f0391 + e30720b commit 4634be8ba6176e71579fa01f5fd2c74e41eedad6 @mcostalba committed Apr 16, 2009
Showing with 118 additions and 33 deletions.
  1. +118 −33 src/search.cpp
View
@@ -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 search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
- Depth depth, int ply, int threadID);
- Value search(Position &pos, SearchStack ss[], Value beta,
- Depth depth, int ply, bool allowNullmove, int threadID);
- Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
- Depth depth, int ply, int threadID);
+ Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta);
+ Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
+ Value search(Position &pos, SearchStack ss[], Value beta, 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);
- ValueByIteration[1] = rml.get_move_score(0);
+ IterationInfo[1] = IterationInfoType(rml.get_move_score(0), 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(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
+ && abs(IterationInfo[Iteration].value) >= 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 beta = VALUE_INFINITE, value;
+ Value oldAlpha = alpha;
+ 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;
- alpha = value;
+ 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)
- || ( !FailHigh && !fail_high_ply_1() && !Problem
+ || (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
+ || ( !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) ||
- (!FailHigh && !fail_high_ply_1() && !Problem &&
+ t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
+ (!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
t > 6*(MaxSearchTime + ExtraSearchTime)))))
AbortSearch = true;
}

0 comments on commit 4634be8

Please sign in to comment.