From c5d0019c6d7f43a46f409b9e7664eb2eaae1a1cd Mon Sep 17 00:00:00 2001
From: Fabian Fichter <ianfab@users.noreply.github.com>
Date: Sat, 12 Jan 2019 19:18:45 +0100
Subject: [PATCH] Support prohibition of perpetual check

Completes the rule implementation of shogi variants.
---
 src/position.cpp |    6 +++++-
 src/variant.cpp  |    1 +
 src/variant.h    |    1 +
 3 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/src/position.cpp b/src/position.cpp
index 9922efc..29ce04d 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1561,17 +1561,21 @@ bool Position::is_optional_game_end(Value& result, int ply) const {
 
       StateInfo* stp = st->previous->previous;
       int cnt = 0;
+      bool perpetual = true;
 
       for (int i = 4; i <= end; i += 2)
       {
           stp = stp->previous->previous;
+          perpetual &= bool(stp->checkersBB);
 
           // Return a draw score if a position repeats once earlier but strictly
           // after the root, or repeats twice before or at the root.
           if (   stp->key == st->key
               && ++cnt + 1 == (ply > i ? 2 : n_fold_rule()))
           {
-              result = convert_mate_value(var->nFoldValueAbsolute && sideToMove == BLACK ? -var->nFoldValue : var->nFoldValue, ply);
+              result = convert_mate_value(  var->perpetualCheckIllegal && perpetual ? VALUE_MATE
+                                          : var->nFoldValueAbsolute && sideToMove == BLACK ? -var->nFoldValue
+                                          : var->nFoldValue, ply);
               return true;
           }
       }
diff --git a/src/variant.cpp b/src/variant.cpp
index 84260f5..14e2d9e 100644
--- a/src/variant.cpp
+++ b/src/variant.cpp
@@ -271,6 +271,7 @@ VariantMap variants; // Global object
         v->stalemateValue = -VALUE_MATE;
         v->nFoldRule = 4;
         v->nMoveRule = 0;
+        v->perpetualCheckIllegal = true;
         return v;
     }
     Variant* minishogi_variant() {
diff --git a/src/variant.h b/src/variant.h
index cd7421f..9fa1c0f 100644
--- a/src/variant.h
+++ b/src/variant.h
@@ -73,6 +73,7 @@ struct Variant {
   int nFoldRule = 3;
   Value nFoldValue = VALUE_DRAW;
   bool nFoldValueAbsolute = false;
+  bool perpetualCheckIllegal = false;
   Value stalemateValue = VALUE_DRAW;
   Value checkmateValue = -VALUE_MATE;
   bool shogiPawnDropMateIllegal = false;
-- 
1.7.0.4