From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 19 May 2012 07:38:23 +0000 (+0100)
Subject: Add a known draw case in kpk bitbase generation
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=0ecc920a09f479cb9b568716597e0756da557174;hp=f86182e791d0ff9d490556a06f9ae3f8770ff55d

Add a known draw case in kpk bitbase generation

Early classify as known draws the positions
where white king is trapped on the rook file.

Suggested by Dan Honeycutt.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/bitbase.cpp b/src/bitbase.cpp
index b01a03d4..ceb94a0f 100644
--- a/src/bitbase.cpp
+++ b/src/bitbase.cpp
@@ -156,7 +156,7 @@ namespace {
         && rank_of(psq) < RANK_7)
         return DRAW;
 
-    //  Case 4: White king in front of pawn and black has opposition
+    // Case 4: White king in front of pawn and black has opposition
     if (   stm == WHITE
         && wksq == psq + DELTA_N
         && bksq == wksq + DELTA_N + DELTA_N
@@ -168,6 +168,13 @@ namespace {
         && file_of(psq) == FILE_A)
         return DRAW;
 
+    // Case 6: White king trapped on the rook file
+    if (   file_of(wksq) == FILE_A
+        && file_of(psq) == FILE_A
+        && rank_of(wksq) > rank_of(psq)
+        && bksq == wksq + 2)
+        return DRAW;
+
     return UNKNOWN;
   }