From c3acf44ac8dce310b1d599071fb1ace1ed39671d Mon Sep 17 00:00:00 2001
From: Peter Osterlund <peterosterlund2@gmail.com>
Date: Thu, 3 Jul 2014 09:22:16 +0000
Subject: [PATCH] DroidFish: Workaround for GTB en passant probing bug.

---
 .../petero/droidfish/gamelogic/MoveGen.java   |  2 +-
 .../src/org/petero/droidfish/gtb/Probe.java   | 33 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/DroidFish/src/org/petero/droidfish/gamelogic/MoveGen.java b/DroidFish/src/org/petero/droidfish/gamelogic/MoveGen.java
index dadcd96..7852ab0 100644
--- a/DroidFish/src/org/petero/droidfish/gamelogic/MoveGen.java
+++ b/DroidFish/src/org/petero/droidfish/gamelogic/MoveGen.java
@@ -26,7 +26,7 @@ import java.util.ArrayList;
  * @author petero
  */
 public class MoveGen {
-    static MoveGen instance;
+    public static MoveGen instance;
     static {
         instance = new MoveGen();
     }
diff --git a/DroidFish/src/org/petero/droidfish/gtb/Probe.java b/DroidFish/src/org/petero/droidfish/gtb/Probe.java
index 059229d..6b785b2 100644
--- a/DroidFish/src/org/petero/droidfish/gtb/Probe.java
+++ b/DroidFish/src/org/petero/droidfish/gtb/Probe.java
@@ -72,6 +72,39 @@ public class Probe {
      * @return True if success.
      */
     public final ProbeResult probeHard(Position pos) {
+        ProbeResult ret = probeHardRaw(pos);
+        if (ret.result == ProbeResult.DRAW && pos.getEpSquare() != -1) {
+            ArrayList<Move> moveList = MoveGen.instance.legalMoves(pos);
+            int pawn = pos.whiteMove ? Piece.WPAWN : Piece.BPAWN;
+            int maxMate = -1;
+            UndoInfo ui = new UndoInfo();
+            for (Move move : moveList) {
+                if ((move.to != pos.getEpSquare()) || (pos.getPiece(move.from) != pawn))
+                    return ret;
+                pos.makeMove(move, ui);
+                ProbeResult ret2 = probeHard(pos);
+                pos.unMakeMove(move, ui);
+                switch (ret2.result) {
+                case ProbeResult.DRAW:
+                    break;
+                case ProbeResult.WMATE:
+                case ProbeResult.BMATE:
+                    maxMate = Math.max(maxMate, ret2.movesToMate);
+                    break;
+                case ProbeResult.UNKNOWN:
+                    ret.result = ProbeResult.UNKNOWN;
+                    return ret;
+                }
+            }
+            if (maxMate != -1) {
+                ret.result = pos.whiteMove ? ProbeResult.BMATE : ProbeResult.WMATE;
+                ret.movesToMate = maxMate;
+            }
+        }
+        return ret;
+    }
+
+    private final ProbeResult probeHardRaw(Position pos) {
         int castleMask = 0;
         if (pos.a1Castle()) castleMask |= GtbProbe.A1_CASTLE;
         if (pos.h1Castle()) castleMask |= GtbProbe.H1_CASTLE;