// evaluation of the position is more than NullMoveMargin below beta.
const Value NullMoveMargin = Value(0x300);
- //Null move search refutes move when Nullvalue >= Beta - Delta. Index is depth
- //in full plies. Last index is 9+.
- const Value NullMoveDeltaMidgame[] =
- { Value(-8), Value( 6), Value(-15), Value( 9), Value(21),
- Value(34), Value(54), Value( 59), Value(61), Value(61) };
-
- const Value NullMoveDeltaEndgame[] =
- { Value( 6), Value( 0), Value(-13), Value(-9), Value(-35),
- Value(12), Value(24), Value( 9), Value( 5), Value( 5) };
-
// Pruning criterions. See the code and comments in ok_to_prune() to
// understand their precise meaning.
const bool PruneEscapeMoves = false;
&& ok_to_do_nullmove(pos)
&& approximateEval >= beta - NullMoveMargin)
{
- //Calculate correct delta. Idea and tuning from Joona Kiiski.
- ScaleFactor factor[2] = { SCALE_FACTOR_NORMAL, SCALE_FACTOR_NORMAL };
- Phase phase = pos.game_phase();
- int i = Min(depth / OnePly, 9);
- Value delta = scale_by_game_phase(NullMoveDeltaMidgame[i], NullMoveDeltaEndgame[i], phase, factor);
-
ss[ply].currentMove = MOVE_NULL;
StateInfo st;
pos.do_null_move(st);
int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
- Value nullValue = -search(pos, ss, -(beta-delta-1), depth-R*OnePly, ply+1, false, threadID);
+ Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
pos.undo_null_move();
{
/* Do not return unproven mates */
}
- else if (nullValue >= beta - delta)
+ else if (nullValue >= beta)
{
if (depth < 6 * OnePly)
return beta;