This patch simplifies the control flow in search(), removing an if
and a goto. A side effect of the patch is that Stockfish is now a
little bit more selective at low depths, because we allow razoring,
futility pruning and probcut pruning after a null move.
passed STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 32035 W: 6523 L: 6422 D: 19090
http://tests.stockfishchess.org/tests/view/
5af142ca0ebc597fb3d39bb6
passed LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 41431 W: 6187 L: 6097 D: 29147
http://tests.stockfishchess.org/tests/view/
5af148770ebc597fb3d39bc1
Ideas for further work:
• Use the nodes credit opened by the patch (the increased selectivity)
to try somewhat higher razoring, futility or probcut margins at [0..4].
Bench:
4855031
- // Step 6. Evaluate the position statically
+ // Step 6. Static evaluation of the position
if (inCheck)
{
ss->staticEval = eval = VALUE_NONE;
improving = false;
if (inCheck)
{
ss->staticEval = eval = VALUE_NONE;
improving = false;
+ goto moves_loop; // Skip early pruning when in check
ss->staticEval, TT.generation());
}
ss->staticEval, TT.generation());
}
- improving = ss->staticEval >= (ss-2)->staticEval
- ||(ss-2)->staticEval == VALUE_NONE;
-
- if (ss->excludedMove || !pos.non_pawn_material(pos.side_to_move()))
- goto moves_loop;
-
- // Step 7. Razoring (skipped when in check, ~2 Elo)
+ // Step 7. Razoring (~2 Elo)
if ( !PvNode
&& depth < 3 * ONE_PLY
&& eval <= alpha - RazorMargin[depth / ONE_PLY])
if ( !PvNode
&& depth < 3 * ONE_PLY
&& eval <= alpha - RazorMargin[depth / ONE_PLY])
- // Step 8. Futility pruning: child node (skipped when in check, ~30 Elo)
+ improving = ss->staticEval >= (ss-2)->staticEval
+ || (ss-2)->staticEval == VALUE_NONE;
+
+ // Step 8. Futility pruning: child node (~30 Elo)
if ( !rootNode
&& depth < 7 * ONE_PLY
&& eval - futility_margin(depth, improving) >= beta
if ( !rootNode
&& depth < 7 * ONE_PLY
&& eval - futility_margin(depth, improving) >= beta
&& (ss-1)->statScore < 30000
&& eval >= beta
&& ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
&& (ss-1)->statScore < 30000
&& eval >= beta
&& ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+ && !ss->excludedMove
+ && pos.non_pawn_material(pos.side_to_move())
&& (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))
{
assert(eval - beta >= 0);
&& (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))
{
assert(eval - beta >= 0);
- // Step 10. ProbCut (skipped when in check, ~10 Elo)
+ // Step 10. ProbCut (~10 Elo)
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
- // Step 11. Internal iterative deepening (skipped when in check, ~2 Elo)
+ // Step 11. Internal iterative deepening (~2 Elo)
if ( depth >= 8 * ONE_PLY
&& !ttMove)
{
if ( depth >= 8 * ONE_PLY
&& !ttMove)
{