NetHack self-improving Banes patch

diff --git a/include/extern.h b/include/extern.h
index e8285c0..4e2af9a 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -98,6 +98,7 @@ E void FDECL(retouch_equipment, (int));
 E void NDECL(mkot_trap_warn);
 E boolean FDECL(is_magic_key, (struct monst *, struct obj *));
 E struct obj *FDECL(has_magic_key, (struct monst *));
+E void FDECL(empower_artifact, (struct obj *, struct monst *, BOOLEAN_P));

 /* ### attrib.c ### */

diff --git a/src/artifact.c b/src/artifact.c
index 03573fe..045d727 100644
--- a/src/artifact.c
+++ b/src/artifact.c
@@ -2202,4 +2202,75 @@ struct monst *mon; /* if null, hero assumed */
     return (struct obj *) 0;
 }

+/* Let some artifacts grow in power upon slaying a hated foe. */
+void
+empower_artifact(weapon, victim, silent)
+struct obj *weapon;
+struct monst *victim;
+boolean silent;
+{
+    int chance = 10, tries = 1;
+    const struct artifact *artifact = get_artifact(weapon);
+    if (!artifact || weapon->oclass != WEAPON_CLASS
+        || !bane_applies(artifact, victim))
+        return;
+    if (artifact->spfx & SPFX_DFLAG2) {
+        /* some artifacts have way too common victims -- balance */
+        switch (artifact->mtype) {
+            case M2_ELF:
+                /* somewhat common, moderate levels, mediocre artifact */
+                chance = 25;
+                break;
+            case M2_ORC:
+                /* very common, weak, both artifacts are mundane */
+                chance = 30;
+                break;
+            case M2_DEMON:
+                /* common in hell, can be strong, but artifact is
+                 * hardly better than an ordinary silver saber */
+                chance = 40;
+                break;
+            case M2_UNDEAD:
+                /* very common, can be strong, artifact is actually useful */
+                chance = 60;
+                break;
+            default:
+                /* other banes have rare enough victims */
+                break;
+        }
+    } else if (artifact->spfx & SPFX_DALIGN) {
+        /* Sceptre of Might: really stretching it,
+         * but let's throw a bone to illiterate cavepeople */
+        chance = 1000; /* victims incredibly common, so make it rare */
+    }
+    if (victim->mrevived || victim->mcloned) {
+        /* penalize farming dragons/giants/etc. with turn undead */
+        int died = mvitals[monsndx(victim->data)].died;
+        int counter, step;
+        /* almost the same formula as for experience */
+        for (counter = 1, step = 0; step < died; counter++) {
+            chance += chance;
+            died -= step;
+            if (counter & 1)
+                step += 20;
+        }
+    } else if (victim->data->geno & G_UNIQ)
+        tries += rnd(3); /* up to +4 at once, but +2 more likely */
+    while (tries--) {
+        int plus = weapon->spe;
+        if (plus == 127)
+            break; /* not very likely, but let's not ruin anyone's game */
+        if (rn2(victim->m_lev + chance) < chance) /* level : chance odds */
+            continue;
+        /* penalize "unsafe" enchantments, with a discount for +6 -> +7 */
+        if (plus == 6 && rn2(2) || plus > 6 && rn2(5) || plus > 8 && rn2(plus))
+            continue;
+        if (!silent) {
+            pline("%s looks more powerful!", Yname2(weapon));
+            silent = TRUE;
+        }
+        weapon->spe++;
+    }
+}
+
 /*artifact.c*/
diff --git a/src/mhitm.c b/src/mhitm.c
index 5ebbd84..6ae64f8 100644
--- a/src/mhitm.c
+++ b/src/mhitm.c
@@ -543,6 +543,7 @@ struct attack *mattk;
             silverhit = (weaponhit && otmp
                          && objects[otmp->otyp].oc_material == SILVER),
             showit = FALSE;
+    int result;

     /* unhiding or unmimicking happens even if hero can't see it
        because the formerly concealed monster is now in action */
@@ -637,7 +638,10 @@ struct attack *mattk;
     } else
         noises(magr, mattk);

-    return mdamagem(magr, mdef, mattk);
+    result = mdamagem(magr, mdef, mattk);
+    if (weaponhit && result & MM_DEF_DIED)
+        empower_artifact(otmp, mdef, !vis);
+    return result;
 }

 /* Returns the same values as mdamagem(). */
diff --git a/src/uhitm.c b/src/uhitm.c
index 2eedb18..7b72776 100644
--- a/src/uhitm.c
+++ b/src/uhitm.c
@@ -1327,6 +1327,8 @@ int dieroll;
                 pline("%s appears confused.", Monnam(mon));
         }
     }
+    if (destroyed)
+        empower_artifact(obj, mon, FALSE);
     if (unpoisonmsg)
         Your("%s %s no longer poisoned.", saved_oname,
              vtense(saved_oname, "are"));