Abstract out some state arithmetic.

actions.c

@@ -361,7 +361,7 @@ static int vcarry(token_t verb, token_t obj)
 
     }
 
-    if (obj == BIRD && game.prop[BIRD] != BIRD_CAGED && -1 - game.prop[BIRD] != BIRD_CAGED) {
+    if (obj == BIRD && game.prop[BIRD] != BIRD_CAGED && STASHED(BIRD) != BIRD_CAGED) {
         if (game.prop[BIRD] == BIRD_FOREST_UNCAGED) {
             DESTROY(BIRD);
             rspeak(BIRD_CRAP);
@@ -380,8 +380,7 @@ static int vcarry(token_t verb, token_t obj)
     /* FIXME: Arithmetic on state numbers */
     if ((obj == BIRD ||
          obj == CAGE) &&
-        (game.prop[BIRD] == BIRD_CAGED ||
-         -1 - game.prop[BIRD] == 1))
+        (game.prop[BIRD] == BIRD_CAGED || STASHED(BIRD) == BIRD_CAGED))
         carry(BIRD + CAGE - obj, game.loc);
     carry(obj, game.loc);
     if (obj == BOTTLE && LIQUID() != NO_OBJECT)

advent.h

@@ -29,6 +29,11 @@
 #define STATE_NOTFOUND  -1	  // 'Not found" state of treasures */
 #define STATE_GROUND	0	  // After discovered, before messed with
 
+/* Map a state property value to a negative range, where the object cannot be
+ * picked up but the value can be recovered later.  Avoid colliding with -1,
+ * which has its own meaning. */
+#define STASHED(obj)	(-1 - game.prop[obj])
+
 /*
  *  MOD(N,M)    = Arithmetic modulus
  *  AT(OBJ)     = true if on either side of two-placed object

main.c

@@ -1028,7 +1028,7 @@ L2600:
                 pspeak(OYSTER, look, 1, true);
             for (size_t i = 1; i <= NOBJECTS; i++) {
                 if (TOTING(i) && game.prop[i] < 0)
-                    game.prop[i] = -1 - game.prop[i];
+                    game.prop[i] = STASHED(i);
             }
         }
         game.wzdark = DARK(game.loc);