pull request #1175 - obj->corpsenm fixes

Pull request by mkuoppal:  some objects which use the corpsenm field
to access the mons[] array can have a corpsenm value of NON_PM (-1)
and weren't avoiding array access in those cases.

In addition to a fixes entry for it, this makes some revisions to the
commited code, handling a few of the cases differently.

Closes #1175

doc/fixes3-7-0.txt

@@ -1348,6 +1348,7 @@ if polymorphing a potion turned it into oil, dipping potions produced oil
 	into non-oil kept its relative age (no noticeable effect though)
 an engulfer capable of passing through iron bars could do so even when hero
 	was engulfed
+some uses of mons[obj->corpsenm] weren't excluding obj->corpsenm==NON_PM (-1)
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

include/mondata.h

@@ -199,6 +199,8 @@
 
 #define touch_petrifies(ptr) \
     ((ptr) == &mons[PM_COCKATRICE] || (ptr) == &mons[PM_CHICKATRICE])
+/* Medusa doesn't pass touch_petrifies() but does petrify if eaten */
+#define flesh_petrifies(pm) (touch_petrifies(pm) || (pm) == &mons[PM_MEDUSA])
 
 /* missiles made of rocks don't harm these: xorns and earth elementals
    (but not ghosts and shades because that would impact all missile use

src/dog.c

@@ -929,17 +929,16 @@ dogfood(struct monst *mon, struct obj *obj)
     switch (obj->oclass) {
     case FOOD_CLASS:
         fx = (obj->otyp == CORPSE || obj->otyp == TIN || obj->otyp == EGG)
+                /* corpsenm might be NON_PM (special tin, unhatachable egg) */
                 ? obj->corpsenm
-                : NUMMONS; /* valid mons[mndx] to pacify static analyzer */
-
-        fptr = fx >= LOW_PM ? &mons[fx] : NULL;
+                : NON_PM;
+        /* mons[NUMMONS] is valid; predicate tests against it will fail */
+        fptr = &mons[(fx >= LOW_PM) ? fx : NUMMONS];
 
         if (obj->otyp == CORPSE && is_rider(fptr))
             return TABU;
         if ((obj->otyp == CORPSE || obj->otyp == EGG)
-            /* Medusa's corpse doesn't pass the touch_petrifies() test
-               but does cause petrification if eaten */
-            && ((fptr && touch_petrifies(fptr)) || obj->corpsenm == PM_MEDUSA)
+            && flesh_petrifies(fptr) /* c*ckatrice or Medusa */
             && !resists_ston(mon))
             return POISON;
         if (obj->otyp == LUMP_OF_ROYAL_JELLY

src/eat.c

@@ -48,9 +48,6 @@ static int tin_ok(struct obj *);
 /* also used to see if you're allowed to eat cats and dogs */
 #define CANNIBAL_ALLOWED() (Role_if(PM_CAVE_DWELLER) || Race_if(PM_ORC))
 
-/* monster types that cause hero to be turned into stone if eaten */
-#define flesh_petrifies(pm) (touch_petrifies(pm) || (pm) == &mons[PM_MEDUSA])
-
 /* Rider corpses are treated as non-rotting so that attempting to eat one
    will be sure to reach the stage of eating where that meal is fatal;
    acid blob corpses eventually rot away to nothing but before that happens
@@ -58,7 +55,7 @@ static int tin_ok(struct obj *);
    become rotten */
 #define nonrotting_corpse(mnum) \
     ((mnum) == PM_LIZARD || (mnum) == PM_LICHEN \
-     || ((mnum) >= LOW_PM && is_rider(&mons[mnum])) \
+     || is_rider(&mons[mnum])                   \
      || (mnum) == PM_ACID_BLOB)
 
 /* non-rotting non-corpses; unlike lizard corpses, these items will behave
@@ -1415,12 +1412,12 @@ tin_details(struct obj *obj, int mnum, char *buf)
 void
 set_tin_variety(struct obj *obj, int forcetype)
 {
-    register int r;
+    int r, mnum = obj->corpsenm;
 
     if (forcetype == SPINACH_TIN
         || (forcetype == HEALTHY_TIN
-            && (obj->corpsenm == NON_PM /* empty or already spinach */
-                || !vegetarian(&mons[obj->corpsenm])))) { /* replace meat */
+            && (mnum == NON_PM /* empty or already spinach */
+                || !vegetarian(&mons[mnum])))) { /* replace meat */
         obj->corpsenm = NON_PM; /* not based on any monster */
         obj->spe = 1;           /* spinach */
         return;
@@ -1434,17 +1431,18 @@ set_tin_variety(struct obj *obj, int forcetype)
         r = forcetype;
     } else {               /* RANDOM_TIN */
         r = rn2(TTSZ - 1); /* take your pick */
-        if (r == ROTTEN_TIN && nonrotting_corpse(obj->corpsenm))
+        if (r == ROTTEN_TIN && (mnum >= LOW_PM && nonrotting_corpse(mnum)))
             r = HOMEMADE_TIN; /* lizards don't rot */
     }
     obj->spe = -(r + 1); /* offset by 1 to allow index 0 */
 }
 
 static int
-tin_variety(struct obj *obj,
-            boolean displ) /* we're just displaying so leave things alone */
+tin_variety(
+    struct obj *obj,
+    boolean displ) /* we're just displaying so leave things alone */
 {
-    register int r;
+    int r, mnum = obj->corpsenm;
 
     if (obj->spe == 1) {
         r = SPINACH_TIN;
@@ -1453,13 +1451,14 @@ tin_variety(struct obj *obj,
     } else if (obj->spe < 0) {
         r = -(obj->spe);
         --r; /* get rid of the offset */
-    } else
+    } else {
         r = rn2(TTSZ - 1);
+    }
 
     if (!displ && r == HOMEMADE_TIN && !obj->blessed && !rn2(7))
         r = ROTTEN_TIN; /* some homemade tins go bad */
 
-    if (r == ROTTEN_TIN && nonrotting_corpse(obj->corpsenm))
+    if (r == ROTTEN_TIN && (mnum >= LOW_PM && nonrotting_corpse(mnum)))
         r = HOMEMADE_TIN; /* lizards don't rot */
     return r;
 }
@@ -1762,12 +1761,15 @@ eatcorpse(struct obj *otmp)
     int retcode = 0, tp = 0, mnum = otmp->corpsenm;
     long rotted = 0L;
     int ll_conduct = 0;
-    boolean stoneable = (flesh_petrifies(&mons[mnum]) && !Stone_resistance
-                         && !poly_when_stoned(gy.youmonst.data)),
+    boolean stoneable,
             slimeable = (mnum == PM_GREEN_SLIME && !Slimed && !Unchanging
                          && !slimeproof(gy.youmonst.data)),
             glob = otmp->globby ? TRUE : FALSE;
 
+    assert(mnum >= LOW_PM);
+    stoneable = (flesh_petrifies(&mons[mnum]) && !Stone_resistance
+                 && !poly_when_stoned(gy.youmonst.data));
+
     /* KMH, conduct */
     if (!vegan(&mons[mnum]))
         if (!u.uconduct.unvegan++) {

src/mon.c

@@ -11,7 +11,6 @@ static void sanity_check_single_mon(struct monst *, boolean, const char *);
 static struct obj *make_corpse(struct monst *, unsigned);
 static int minliquid_core(struct monst *);
 static void m_calcdistress(struct monst *);
-static boolean mstoning(const struct obj *obj);
 static boolean monlineu(struct monst *, int, int);
 static long mm_2way_aggression(struct monst *, struct monst *);
 static long mm_aggression(struct monst *, struct monst *);
@@ -1157,24 +1156,13 @@ meatbox(struct monst *mon, struct obj *otmp)
     }
 }
 
-static boolean
-mstoning(const struct obj *obj)
-{
-    const int nm = obj->corpsenm;
+#define mstoning(obj) \
+    (ofood(obj) && obj->corpsenm >= LOW_PM      \
+     && flesh_petrifies(&mons[obj->corpsenm]))
 
-    if (nm < LOW_PM)
-        return FALSE;
-
-    if (nm == PM_MEDUSA)
-        return TRUE;
-
-    return ofood(obj) && touch_petrifies(&mons[nm]);
-}
-
-/* monster consumes an object.
-
-   monster may die, polymorph, grow up, heal, etc; meating is not changed.
-   object is extracted from any linked list and freed. */
+/* Monster mtmp consumes an object.
+   Monster may die, polymorph, grow up, heal, etc; meating is not changed.
+   Object is extracted from any linked list and freed. */
 void
 m_consume_obj(struct monst *mtmp, struct obj *otmp)
 {
@@ -1429,8 +1417,10 @@ meatobj(struct monst* mtmp) /* for gelatinous cubes */
     return (count > 0 || ecount > 0) ? 1 : 0;
 }
 
+#undef mstoning
+
 /* Monster eats a corpse off the ground.
- * Return value is 0 = nothing eaten, 1 = ate a corpse, 2 = died */
+   Return value is 0 = nothing eaten, 1 = ate a corpse, 2 = died. */
 int
 meatcorpse(
     struct monst *mtmp) /* for purple worms and other voracious monsters */