Ported the ring of carrying from xNetHack.

From d70ba212dabc10ab3d08977a123ffdabbd76caa1.

Instead of granting +/- 5% per level of enchantment, I've bumped it up to 10%.

include/extern.h

@@ -590,6 +590,7 @@ E int FDECL(destroy_arm, (struct obj *, BOOLEAN_P));
 E void FDECL(adj_abon, (struct obj *, SCHAR_P));
 E boolean
 FDECL(inaccessible_equipment, (struct obj *, const char *, BOOLEAN_P));
+E int FDECL(ringbon, (SHORT_P));
 
 /* ### dog.c ### */
 

src/do_wear.c

@@ -4177,5 +4177,24 @@ toggle_armor_light(struct obj *armor, boolean on)
     }
 }
 
-
+/* Computes magical bonus from worn rings of a specific type.
+ * Intended for things that give numerical bonuses; could theoretically be
+ * extended later if other equipment confers a similar bonus. */
+int
+ringbon(ring_typ)
+short ring_typ;
+{
+    int bon = 0;
+    if (!objects[ring_typ].oc_charged) {
+        impossible("ringbon: called with non-chargeable ring?");
+        return 0;
+    }
+    if (uleft && uleft->otyp == ring_typ) {
+        bon += uleft->spe;
+    }
+    if (uright && uright->otyp == ring_typ) {
+        bon += uright->spe;
+    }
+    return bon;
+}
 /*do_wear.c*/

src/hack.c

@@ -3696,6 +3696,11 @@ weight_cap()
         float_vs_flight();
     }
 
+    /* final adjustment: ring of carrying lets you carry more than usual and go
+     * over the normal carrycap */
+    int pct_increase = ringbon(RIN_CARRYING) * 10;
+    carrcap = (carrcap * (100 + pct_increase)) / 100;
+
     return (int) carrcap;
 }
 

src/objects.c

@@ -720,6 +720,7 @@ RING("protection", "black onyx",                 PROTECTION,               100,
            regardless of ring's enchantment; wearing a second ring of
            protection (or even one ring of protection combined with
            cloak of protection) doesn't give a second MC boost */
+RING("carrying", "glittery",                     0,                        200, 1, 1, 1,  7, GEMSTONE, CLR_WHITE),
 RING("regeneration", "moonstone",                REGENERATION,             200, 1, 1, 0,  6, MINERAL, HI_MINERAL),
 RING("searching", "tiger eye",                   SEARCHING,                200, 1, 1, 0,  6, GEMSTONE, CLR_BROWN),
 RING("stealth", "jade",                          STEALTH,                  100, 1, 1, 0,  6, GEMSTONE, CLR_GREEN),