Reduce code duplication in extrinsics-protect-items code

The same checks were being repeated for every damage type; this
sends them through two centralised functions (one for checking
whether an extrinsic blocks a specific instance of item destruction
and one for the enlightenment message), so that new mechanisms of
item destruction prevention will need to change only one point in
the code.

include/extern.h

@@ -3582,7 +3582,8 @@ extern void melt_ice_away(union any *, long);
 extern int zap_over_floor(coordxy, coordxy, int, boolean *, boolean, short);
 extern void fracture_rock(struct obj *);
 extern boolean break_statue(struct obj *);
-extern boolean u_adtyp_resistance_obj(int);
+extern int u_adtyp_resistance_obj(int);
+extern boolean inventory_resistance_check(int);
 extern char *item_what(int);
 extern void destroy_item(int, int);
 extern int destroy_mitem(struct monst *, int, int);

src/dothrow.c

@@ -2524,8 +2524,9 @@ breakobj(
 }
 
 /*
- * Check to see if obj is going to break, but don't actually break it.
- * Return 0 if the object isn't going to break, 1 if it is.
+ * Check to see if obj (which has just hit hard something at speed, e.g.
+ * thrown or dropped from height) is going to break, but don't actually
+ * break it. Return 0 if the object isn't going to break, 1 if it is.
  */
 boolean
 breaktest(struct obj *obj)

src/insight.c

@@ -1429,6 +1429,19 @@ weapon_insight(int final)
     } /* skill applies */
 }
 
+static void
+item_resistance_message(int adtyp, const char *prot_message, int final)
+{
+    int protection = u_adtyp_resistance_obj(adtyp);
+    if (protection) {
+        boolean somewhat = protection < 99;
+        enl_msg("Your items ",
+                somewhat ? "are somewhat" : "are",
+                somewhat ? "were somewhat" : "were",
+                prot_message, item_what(adtyp));
+    }
+}
+
 /* attributes: intrinsics and the like, other non-obvious capabilities */
 static void
 attributes_enlightenment(int unused_mode UNUSED, int final)
@@ -1469,26 +1482,18 @@ attributes_enlightenment(int unused_mode UNUSED, int final)
         you_are("magic-protected", from_what(ANTIMAGIC));
     if (Fire_resistance)
         you_are("fire resistant", from_what(FIRE_RES));
-    if (u_adtyp_resistance_obj(AD_FIRE))
-        enl_msg("Your items ", "are", "were", " protected from fire",
-                item_what(AD_FIRE));
+    item_resistance_message(AD_FIRE, " protected from fire", final);
     if (Cold_resistance)
         you_are("cold resistant", from_what(COLD_RES));
-    if (u_adtyp_resistance_obj(AD_COLD))
-        enl_msg("Your items ", "are", "were", " protected from cold",
-                item_what(AD_COLD));
+    item_resistance_message(AD_COLD, " protected from cold", final);
     if (Sleep_resistance)
         you_are("sleep resistant", from_what(SLEEP_RES));
     if (Disint_resistance)
         you_are("disintegration resistant", from_what(DISINT_RES));
-    if (u_adtyp_resistance_obj(AD_DISN))
-        enl_msg("Your items ", "are", "were",
-                " protected from disintegration", item_what(AD_DISN));
+    item_resistance_message(AD_DISN, " protected from disintegration", final);
     if (Shock_resistance)
         you_are("shock resistant", from_what(SHOCK_RES));
-    if (u_adtyp_resistance_obj(AD_ELEC))
-        enl_msg("Your items ", "are", "were",
-                " protected from electric shocks", item_what(AD_ELEC));
+    item_resistance_message(AD_ELEC, " protected from electric shocks", final);
     if (Poison_resistance)
         you_are("poison resistant", from_what(POISON_RES));
     if (Acid_resistance) {
@@ -1497,9 +1502,7 @@ attributes_enlightenment(int unused_mode UNUSED, int final)
                 "acid resistant");
         you_are(buf, from_what(ACID_RES));
     }
-    if (u_adtyp_resistance_obj(AD_ACID))
-        enl_msg("Your items ", "are", "were", " protected from acid",
-                item_what(AD_ACID));
+    item_resistance_message(AD_ACID, " protected from acid", final);
     if (Drain_resistance)
         you_are("level-drain resistant", from_what(DRAIN_RES));
     if (Sick_resistance)

src/trap.c

@@ -198,7 +198,7 @@ erode_obj(
 
     switch (type) {
     case ERODE_BURN:
-        if (uvictim && u_adtyp_resistance_obj(AD_FIRE) && rn2(100))
+        if (uvictim && inventory_resistance_check(AD_FIRE))
             return ER_NOTHING;
         vulnerable = is_flammable(otmp);
         check_grease = FALSE;
@@ -215,7 +215,7 @@ erode_obj(
         cost_type = COST_ROT;
         break;
     case ERODE_CORRODE:
-        if (uvictim && u_adtyp_resistance_obj(AD_ACID) && rn2(100))
+        if (uvictim && inventory_resistance_check(AD_ACID))
             return ER_NOTHING;
         vulnerable = is_corrodeable(otmp);
         is_primary = FALSE;
@@ -4362,7 +4362,7 @@ acid_damage(struct obj* obj)
     victim = carried(obj) ? &gy.youmonst : mcarried(obj) ? obj->ocarry : NULL;
     vismon = victim && (victim != &gy.youmonst) && canseemon(victim);
 
-    if (victim == &gy.youmonst && u_adtyp_resistance_obj(AD_ACID) && rn2(100))
+    if (victim == &gy.youmonst && inventory_resistance_check(AD_ACID))
         return;
 
     if (obj->greased) {

src/zap.c

@@ -4317,7 +4317,7 @@ zhitu(
         break;
     case ZT_DEATH:
         if (abstyp == ZT_BREATH(ZT_DEATH)) {
-            boolean disn_prot = u_adtyp_resistance_obj(AD_DISN) && rn2(100);
+            boolean disn_prot = inventory_resistance_check(AD_DISN);
 
             if (Disint_resistance) {
                 You("are not disintegrated.");
@@ -5391,20 +5391,41 @@ adtyp_to_prop(int dmgtyp)
     return 0; /* prop_types start at 1 */
 }
 
-/* is hero wearing or wielding an object with resistance
-   to attack damage type */
-boolean
+/* Is hero wearing or wielding an object with resistance to attack
+   damage type? Returns the percentage protectoin that the object
+   gives. */
+int
 u_adtyp_resistance_obj(int dmgtyp)
 {
     int prop = adtyp_to_prop(dmgtyp);
 
     if (!prop)
-        return FALSE;
+        return 0;
 
     if ((u.uprops[prop].extrinsic & (W_ARMOR | W_ACCESSORY | W_WEP)) != 0)
-        return TRUE;
+        return 99; /* 99% protected */
 
-    return FALSE;
+    return 0;
+}
+
+/* Rolls to see whether an object in inventory resists damage from the
+   given damage type, due to an equipped item protecting it. Use
+   u_adtyp_resistance_obj to discover whether objects are protected in
+   general (e.g. for enlightenment) and this function to actually do
+   the roll to see whether a specific object is protected.
+
+   This function doesn't check for other reasons why an object might
+   be protected; you will usually need to do an obj_resists() call
+   too. */
+boolean
+inventory_resistance_check(int dmgtyp)
+{
+    int prob = u_adtyp_resistance_obj(dmgtyp);
+
+    if (!prob)
+        return FALSE;
+
+    return rn2(100) < prob;
 }
 
 /* for enlightenment; currently only useful in wizard mode; cf from_what() */
@@ -5491,7 +5512,7 @@ destroy_one_item(struct obj *obj, int osym, int dmgtyp)
     quan = 0L;
 
     /* external worn item protects inventory? */
-    if (u_adtyp_resistance_obj(dmgtyp) && rn2(100))
+    if (inventory_resistance_check(dmgtyp))
         return;
 
     switch (dmgtyp) {