diff -r efeb98bc69c9 -r 0c1371488d87 src/chess/rules.h
--- a/src/chess/rules.h	Thu Apr 03 16:07:04 2014 +0200
+++ b/src/chess/rules.h	Fri Apr 04 17:36:42 2014 +0200
@@ -102,7 +102,7 @@
 #define mdst(b,m) b[(m)->torow][(m)->tofile]
 #define msrc(b,m) b[(m)->fromrow][(m)->fromfile]
 
-#define isidx(idx) ((uint8_t)idx < 8)
+#define isidx(idx) ((uint8_t)(idx) < 8)
 
 #define isfile(file) (file >= 'a' && file <= 'h')
 #define isrow(row) (row >= '1' && row <= '8')
@@ -145,6 +145,24 @@
 /**
  * Checks, if a specified field is covered by a piece of a certain color.
  * 
+ * Note: when the field is covered by multiple pieces, this function returns
+ * the first piece it can find.
+ * 
+ * @param gamestate the current game state
+ * @param row row of the field to check
+ * @param file file of the field to check
+ * @param color the color of the piece that should threaten the field
+ * @param threat if not NULL: a pointer to the move structure where
+ * the move that could be performed to capture the field should be stored
+ * @return TRUE, if any piece of the specified color threatens the specified
+ * field (i.e. could capture an opponent piece)
+ */
+_Bool get_any_threat_for(GameState *gamestate, uint8_t row, uint8_t file,
+        uint8_t color, Move *threat);
+
+/**
+ * Checks, if a specified field is covered by a piece of a certain color.
+ * 
  * @param gamestate the current game state
  * @param row row of the field to check
  * @param file file of the field to check
@@ -152,7 +170,8 @@
  * @return TRUE, if any piece of the specified color threatens the specified
  * field (i.e. could capture an opponent piece)
  */
-_Bool is_covered(GameState *gamestate,uint8_t row,uint8_t file,uint8_t color);
+#define is_covered(gamestate, row, file, color) \
+    get_any_threat_for(gamestate, row, file, color, NULL)
 
 /**
  * Evaluates a move syntactically and stores the move data in the specified