return d > 17 ? 0 : 29 * d * d + 138 * d - 134;
}
+ // Add a small random component to draw evaluations to keep search dynamic
+ // and to avoid 3fold-blindness.
+ Value value_draw(Depth depth, Thread* thisThread) {
+ return depth < 4 ? VALUE_DRAW
+ : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1);
+ }
+
// Skill structure is used to implement strength limit
struct Skill {
explicit Skill(int l) : level(l) {}
if (rootDepth >= 5 * ONE_PLY)
{
Value previousScore = rootMoves[pvIdx].previousScore;
- delta = Value(18);
+ delta = Value(20);
alpha = std::max(previousScore - delta,-VALUE_INFINITE);
beta = std::min(previousScore + delta, VALUE_INFINITE);
// Start with a small aspiration window and, in the case of a fail
// high/low, re-search with a bigger window until we don't fail
// high/low anymore.
+ int failedHighCnt = 0;
while (true)
{
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false);
+ Depth adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY);
+ bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
// is done with a stable algorithm because all the values but the
if (mainThread)
{
+ failedHighCnt = 0;
failedLow = true;
Threads.stopOnPonderhit = false;
}
}
else if (bestValue >= beta)
+ {
beta = std::min(bestValue + delta, VALUE_INFINITE);
+ if (mainThread)
+ ++failedHighCnt;
+ }
else
break;
&& !rootNode
&& pos.has_game_cycle(ss->ply))
{
- alpha = VALUE_DRAW;
+ alpha = value_draw(depth, pos.this_thread());
if (alpha >= beta)
return alpha;
}
if ( Threads.stop.load(std::memory_order_relaxed)
|| pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
- return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW;
+ return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
+ : value_draw(depth, pos.this_thread());
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
extension = ONE_PLY;
}
else if ( givesCheck // Check extension (~2 Elo)
- && !moveCountPruning
&& pos.see_ge(move))
extension = ONE_PLY;
break;
}
}
- else if (PvNode && !rootNode && value == alpha)
- update_pv(ss->pv, move, (ss+1)->pv);
}
if (move != bestMove)