update_gains(pos, ss[ply - 1].currentMove, ss[ply - 1].eval, ss[ply].eval);
}
- // Static null move pruning. We're betting that the opponent doesn't have
- // a move that will reduce the score by more than FutilityMargins[int(depth)]
- // if we do a null move.
+ // Step 6. Razoring
+ if ( !value_is_mate(beta)
+ && !isCheck
+ && depth < RazorDepth
+ && staticValue < beta - (0x200 + 16 * depth)
+ && ss[ply - 1].currentMove != MOVE_NULL
+ && ttMove == MOVE_NONE
+ && !pos.has_pawn_on_7th(pos.side_to_move()))
+ {
+ Value rbeta = beta - (0x200 + 16 * depth);
+ Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
+ if (v < rbeta)
+ return v; //FIXME: Logically should be: return (v + 0x200 + 16 * depth);
+ }
+
+ // Step 7. Static null move pruning
+ // We're betting that the opponent doesn't have a move that will reduce
+ // the score by more than fuility_margin(depth) if we do a null move.
if ( !isCheck
&& allowNullmove
&& depth < RazorDepth
&& staticValue - futility_margin(depth, 0) >= beta)
return staticValue - futility_margin(depth, 0);
- // Null move search
+ // Step 8. Null move search with verification search
+ // When we jump directly to qsearch() we do a null move only if static value is
+ // at least beta. Otherwise we do a null move if static value is not more than
+ // NullMoveMargin under beta.
if ( allowNullmove
&& depth > OnePly
&& !isCheck
return beta - 1;
}
}
- // Null move search not allowed, try razoring
- else if ( !value_is_mate(beta)
- && !isCheck
- && depth < RazorDepth
- && staticValue < beta - (NullMoveMargin + 16 * depth)
- && ss[ply - 1].currentMove != MOVE_NULL
- && ttMove == MOVE_NONE
- && !pos.has_pawn_on_7th(pos.side_to_move()))
- {
- Value rbeta = beta - (NullMoveMargin + 16 * depth);
- Value v = qsearch(pos, ss, rbeta-1, rbeta, Depth(0), ply, threadID);
- if (v < rbeta)
- return v;
- }
- // Go with internal iterative deepening if we don't have a TT move
+ // Step 9. Internal iterative deepening
if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
!isCheck && ss[ply].eval >= beta - IIDMargin)
{
- search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
+ search(pos, ss, beta, depth/2, ply, false, threadID);
ttMove = ss[ply].pv[ply];
tte = TT.retrieve(posKey);
}