From 3bd3ef0aeabb59ffa0584a95369b79fdf85822be Mon Sep 17 00:00:00 2001
From: nodchip <nodchip@gmail.com>
Date: Mon, 10 Aug 2020 15:47:11 +0900
Subject: [PATCH] Implemented the code to detect draw by insufficient mating
 material.

---
 src/learn/learner.cpp | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/src/learn/learner.cpp b/src/learn/learner.cpp
index 68bbc835..b81009c7 100644
--- a/src/learn/learner.cpp
+++ b/src/learn/learner.cpp
@@ -579,6 +579,48 @@ void MultiThinkGenSfen::thread_worker(size_t thread_id)
 				}
 			}
 
+			// Draw by insufficient mating material
+			if (pos.count<ALL_PIECES>() <= 4) {
+				int pcnt = pos.count<ALL_PIECES>();
+				// (1) KvK
+				if (pcnt == 2) {
+					if (use_draw_in_training_data_generation)
+						flush_psv(0);
+					break;
+				}
+				// (2) KvK + 1 minor piece
+				if (pcnt == 3) {
+					int minor_pc = pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE) +
+						pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK);
+					if (minor_pc == 1) {
+						if (use_draw_in_training_data_generation)
+							flush_psv(0);
+						break;
+					}
+				}
+				// (3) KBvKB, bishops of the same color
+				else if (pcnt == 4) {
+					if (pos.count<BISHOP>(WHITE) == 1 && pos.count<BISHOP>(BLACK) == 1) {
+						// Color of bishops is black.
+						if ((pos.pieces(WHITE, BISHOP) & DarkSquares)
+							&& (pos.pieces(BLACK, BISHOP) & DarkSquares))
+						{
+							if (use_draw_in_training_data_generation)
+								flush_psv(0);
+							break;
+						}
+						// Color of bishops is white.
+						if ((pos.pieces(WHITE, BISHOP) & ~DarkSquares)
+							&& (pos.pieces(BLACK, BISHOP) & ~DarkSquares))
+						{
+							if (use_draw_in_training_data_generation)
+								flush_psv(0);
+							break;
+						}
+					}
+				}
+			}
+
 			//// constant track
 			//if ((m = book.probe(pos)) != MOVE_NONE)
 			//{