}
}
- // Step 10. If the position doesn't a have ttMove, decrease depth by 2
+ // Step 10. If the position doesn't have a ttMove, decrease depth by 2
// (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
// Use qsearch if depth is equal or below zero (~9 Elo)
if ( PvNode
// then that move is singular and should be extended. To verify this we do
// a reduced search on all the other moves but the ttMove and if the
// result is lower than ttValue minus a margin, then we will extend the ttMove.
+ // Depth margin and singularBeta margin are known for having non-linear scaling.
+ // Their values are optimized to time controls of 180+1.8 and longer
+ // so changing them requires tests at this type of time controls.
if ( !rootNode
&& depth >= 4 - (thisThread->completedDepth > 22) + 2 * (PvNode && tte->is_pv())
&& move == ttMove