From fd91c59d548e6770bf273a44338f7dd3faaaeca3 Mon Sep 17 00:00:00 2001
From: Petr Baudis <pasky@ucw.cz>
Date: Sun, 20 Feb 2011 20:46:39 +0100
Subject: [PATCH] is_middle_ladder(): Factor out middle_ladder_walk()

---
 tactics/ladder.c | 94 ++++++++++++++++++++++++++++++--------------------------
 1 file changed, 51 insertions(+), 43 deletions(-)

diff --git a/tactics/ladder.c b/tactics/ladder.c
index 2acce21..27a1a6a 100644
--- a/tactics/ladder.c
+++ b/tactics/ladder.c
@@ -58,11 +58,60 @@ is_border_ladder(struct board *b, coord_t coord, enum stone lcolor)
 	return true;
 }
 
+
 /* This is very trivial and gets a lot of corner cases wrong.
  * We need this to be just very fast. One important point is
  * that we sometimes might not notice a ladder but if we do,
  * it should always work; thus we can use this for strong
  * negative hinting safely. */
+
+static bool
+middle_ladder_walk(struct board *b, enum stone lcolor, int x, int y, int xd, int yd)
+{
+#define ladder_check(xd1_, yd1_, xd2_, yd2_, xd3_, yd3_)	\
+	if (board_atxy(b, x, y) != S_NONE) { \
+		/* Did we hit a stone when playing out ladder? */ \
+		if (ladder_catcher(b, x, y, lcolor)) \
+			return true; /* ladder works */ \
+		if (board_group_info(b, group_atxy(b, x, y)).lib[0] > 0) \
+			return false; /* friend that's not in atari himself */ \
+	} else { \
+		/* No. So we are at new position. \
+		 * We need to check indirect ladder breakers. */ \
+		/* . 2 x 3 . \
+		 * . x o O 1 <- only at O we can check for o at 2 \
+		 * x o o x .    otherwise x at O would be still deadly \
+		 * o o x . . \
+		 * We check for o and x at 1, these are vital. \
+		 * We check only for o at 2; x at 2 would mean we \
+		 * need to fork (one step earlier). */ \
+		coord_t c = coord_xy(b, x, y); \
+		coord_t c1 = coord_xy(b, x + (xd1_), y + (yd1_)); \
+		enum stone s1 = board_at(b, c1); \
+		if (s1 == lcolor) return false; \
+		if (s1 == stone_other(lcolor)) { \
+			/* One more thing - if the position at 3 is \
+			 * friendly and safe, we escaped anyway! */ \
+			coord_t c3 = coord_xy(b, x + (xd3_), y + (yd3_)); \
+			return board_at(b, c3) != lcolor \
+			       || board_group_info(b, group_at(b, c3)).libs < 2; \
+		} \
+		enum stone s2 = board_atxy(b, x + (xd2_), y + (yd2_)); \
+		if (s2 == lcolor) return false; \
+		if (neighbor_count_at(b, c1, lcolor) + neighbor_count_at(b, c1, S_OFFBOARD) >= 2) \
+			return false; /* It would be self-atari! */ \
+	}
+#define ladder_horiz	do { if (DEBUGL(6)) fprintf(stderr, "%d,%d horiz step (%d,%d)\n", x, y, xd, yd); x += xd; ladder_check(xd, 0, -2 * xd, yd, 0, yd); } while (0)
+#define ladder_vert	do { if (DEBUGL(6)) fprintf(stderr, "%d,%d vert step of (%d,%d)\n", x, y, xd, yd); y += yd; ladder_check(0, yd, xd, -2 * yd, xd, 0); } while (0)
+
+	if (ladder_catcher(b, x - xd, y, lcolor))
+		ladder_horiz;
+	do {
+		ladder_vert;
+		ladder_horiz;
+	} while (1);
+}
+
 bool
 is_middle_ladder(struct board *b, coord_t coord, enum stone lcolor)
 {
@@ -126,47 +175,6 @@ is_middle_ladder(struct board *b, coord_t coord, enum stone lcolor)
 	}
 #undef check_catcher_danger
 #endif
-
-#define ladder_check(xd1_, yd1_, xd2_, yd2_, xd3_, yd3_)	\
-	if (board_atxy(b, x, y) != S_NONE) { \
-		/* Did we hit a stone when playing out ladder? */ \
-		if (ladder_catcher(b, x, y, lcolor)) \
-			return true; /* ladder works */ \
-		if (board_group_info(b, group_atxy(b, x, y)).lib[0] > 0) \
-			return false; /* friend that's not in atari himself */ \
-	} else { \
-		/* No. So we are at new position. \
-		 * We need to check indirect ladder breakers. */ \
-		/* . 2 x 3 . \
-		 * . x o O 1 <- only at O we can check for o at 2 \
-		 * x o o x .    otherwise x at O would be still deadly \
-		 * o o x . . \
-		 * We check for o and x at 1, these are vital. \
-		 * We check only for o at 2; x at 2 would mean we \
-		 * need to fork (one step earlier). */ \
-		coord_t c1 = coord_xy(b, x + (xd1_), y + (yd1_)); \
-		enum stone s1 = board_at(b, c1); \
-		if (s1 == lcolor) return false; \
-		if (s1 == stone_other(lcolor)) { \
-			/* One more thing - if the position at 3 is \
-			 * friendly and safe, we escaped anyway! */ \
-			coord_t c3 = coord_xy(b, x + (xd3_), y + (yd3_)); \
-			return board_at(b, c3) != lcolor \
-			       || board_group_info(b, group_at(b, c3)).libs < 2; \
-		} \
-		enum stone s2 = board_atxy(b, x + (xd2_), y + (yd2_)); \
-		if (s2 == lcolor) return false; \
-		/* Then, can X actually "play" 1 in the ladder? */ \
-		if (neighbor_count_at(b, c1, lcolor) + neighbor_count_at(b, c1, S_OFFBOARD) >= 2) \
-			return false; /* It would be self-atari! */ \
-	}
-#define ladder_horiz	do { if (DEBUGL(6)) fprintf(stderr, "%d,%d horiz step (%d,%d)\n", x, y, xd, yd); x += xd; ladder_check(xd, 0, -2 * xd, yd, 0, yd); } while (0)
-#define ladder_vert	do { if (DEBUGL(6)) fprintf(stderr, "%d,%d vert step of (%d,%d)\n", x, y, xd, yd); y += yd; ladder_check(0, yd, xd, -2 * yd, xd, 0); } while (0)
-
-	if (ladder_catcher(b, x - xd, y, lcolor))
-		ladder_horiz;
-	do {
-		ladder_vert;
-		ladder_horiz;
-	} while (1);
+	
+	return middle_ladder_walk(b, lcolor, x, y, xd, yd);
 }
-- 
2.11.4.GIT