- // Step 17. Late moves reduction / extension (LMR, ~98 Elo)
- // We use various heuristics for the sons of a node after the first son has
- // been searched. In general we would like to reduce them, but there are many
- // cases where we extend a son if it has good chances to be "interesting".
- if ( depth >= 2
- && moveCount > 1 + (PvNode && ss->ply <= 1)
- && ( !ss->ttPv
- || !capture
- || (cutNode && (ss-1)->moveCount > 1)))
- {
- Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
+ // Decrease reduction if position is or has been on the PV
+ // and node is not likely to fail low. (~3 Elo)
+ if ( ss->ttPv
+ && !likelyFailLow)
+ r -= 2;