Support Tsume mode

Allows to solve Tsume puzzles. Example:
```
setoption name TsumeMode value true
setoption name UCI_Variant value shogi
position fen 1kp6/2l6/2l6/2l6/2n6/2n6/1gn6/9/L8[SPPPPPPrrbbgggsssnlppp] w 0 1
d
go mate 20
```

diff --git a/Readme.md b/Readme.md
index c65baf5..f6b481b 100644 (file)
--- a/Readme.md
+++ b/Readme.md
@@ -46,7 +46,7 @@ The games currently supported besides chess are listed below. Fairy-Stockfish ca
 - [Clobber](https://en.wikipedia.org/wiki/Clobber)
 
 ## Installation
-You can download [binary releases](https://github.com/ianfab/Fairy-Stockfish/releases) for Windows and Linux or [compile the program from source](https://github.com/ianfab/Fairy-Stockfish#compiling-stockfish-yourself-from-the-sources). You probably want to use it together with a GUI, see https://github.com/ianfab/Fairy-Stockfish/wiki/Usage for recommendations. Or play against it right away online at https://pychess-variants.herokuapp.com/.
+You can download [binary releases](https://github.com/ianfab/Fairy-Stockfish/releases) for Windows and Linux or [compile the program from source](https://github.com/ianfab/Fairy-Stockfish#compiling-stockfish-yourself-from-the-sources). The program comes without a graphical user interface, so you probably want to use it together with a [compatible GUI](https://github.com/ianfab/Fairy-Stockfish/wiki/Usage). Or play against it right away online at [pychess-variants](https://pychess-variants.herokuapp.com/).
 
 ## UCI parameters
 
@@ -55,7 +55,7 @@ The following UCI options are added or changed compared to official Stockfish:
   * #### UCI_Variant
     The most important option, since it allows to set the variant that is going to be played.
     Most GUIs for chess variants set this option automatically if you select a variant in the GUI,
-    but in case of usage via CLI or via Shogi GUIs the option needs to be set manually.
+    but in case of usage via the CLI the option needs to be set manually.
 
   * #### UCI_Chess960
     Used as a universal flag to switch between Chess960-style shuffling variants (such as Crazyhouse960,
@@ -64,13 +64,18 @@ The following UCI options are added or changed compared to official Stockfish:
 
   * #### Protocol
     Can be used to switch between the supported protocols, namely UCI, UCCI (Xiangqi), USI (Shogi) and XBoard/CECP.
-    This option is automatically set to the respective protocol if a GUI starts communication
+    This option is automatically set to the respective protocol if communication is started
     with one of the `uci`/`ucci`/`usi`/`xboard` commands (as required by the protocols).
 
   * #### VariantPath
     The path to the configuration file for user-defined variants.
     Alternatively, the [`load`](https://github.com/ianfab/Fairy-Stockfish/wiki/Variant-configuration#loading-variant-configuration) command can be used.
 
+  * #### TsumeMode
+    When enabled assumes that the side without a king has to strive for a forced mate, and otherwise loses.
+    This option should be enabled when solving Tsume puzzles, otherwise it might wrongly go for a brinkmate.
+    Although it mainly targets Shogi, the option can be used for any variant where checkmate is the goal.
+
 ## Help
 
 See the [Fairy-Stockfish Wiki](https://github.com/ianfab/Fairy-Stockfish/wiki) for more info, or if the required information is not available, open an [issue](https://github.com/ianfab/Fairy-Stockfish/issues).

diff --git a/src/position.cpp b/src/position.cpp
index e921d83..a673efb 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1915,6 +1915,12 @@ bool Position::is_immediate_game_end(Value& result, int ply) const {
           }
       }
   }
+  // Tsume mode: Assume that side with king wins when not in check
+  if (Options["TsumeMode"] && count<KING>(sideToMove) && !checkers())
+  {
+      result = mate_in(ply);
+      return true;
+  }
 
   return false;
 }

diff --git a/src/ucioption.cpp b/src/ucioption.cpp
index 8a385bf..c101a6e 100644 (file)
--- a/src/ucioption.cpp
+++ b/src/ucioption.cpp
@@ -118,6 +118,7 @@ void init(OptionsMap& o) {
   o["SyzygyProbeDepth"]      << Option(1, 1, 100);
   o["Syzygy50MoveRule"]      << Option(true);
   o["SyzygyProbeLimit"]      << Option(7, 0, 7);
+  o["TsumeMode"]             << Option(false);
   o["VariantPath"]           << Option("<empty>", on_variant_path);
 }