Enable shallow depth pruning for horde chess

horde STC
LLR: 3.36 (-2.94,2.94) [0.00,10.00]
Total: 517 W: 320 L: 196 D: 1
http://35.161.250.236:6543/tests/view/5c2286ad6e23db247289560e

horde LTC
LLR: 2.97 (-2.94,2.94) [0.00,10.00]
Total: 321 W: 213 L: 106 D: 2
http://35.161.250.236:6543/tests/view/5c22a79f6e23db2472895618

giveaway STC
LLR: 3.00 (-2.94,2.94) [-10.00,5.00]
Total: 5940 W: 1928 L: 1914 D: 2098
http://35.161.250.236:6543/tests/view/5c22a7dc6e23db247289561c

giveaway LTC
LLR: 2.96 (-2.94,2.94) [-10.00,5.00]
Total: 4212 W: 1345 L: 1321 D: 1546
http://35.161.250.236:6543/tests/view/5c22aa416e23db2472895622

diff --git a/src/search.cpp b/src/search.cpp
index c82fe32..3b2ef90 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -938,7 +938,7 @@ moves_loop: // When in check, search starts from here
 
       // Step 14. Pruning at shallow depth (~170 Elo)
       if (  !rootNode
-          && pos.non_pawn_material(us)
+          && (pos.non_pawn_material(us) || !(pos.pieces(us) ^ pos.pieces(us, PAWN)))
           && bestValue > VALUE_MATED_IN_MAX_PLY)
       {
           if (   !captureOrPromotion