Rods have an intrinsic recharge rate (#300)

Using Eronarn's proposed system.  Rods get a baseline of 4 MP per 100
turns; every rod has an enchantment, which adds to this.  On top of
that, you get the old Evocations bonus.  At maxed Evocations with a
+9 rod, you gain 52 MP per 100 turns.

Unfortunately, all four of the multi-purpose fields were already used
for rods, so I had to spill enchantment into props.

3 files changed, 40 insertions, 11 deletions

diff --git a/crawl-ref/source/effects.cc b/crawl-ref/source/effects.cc
index 109539cc75..49702e489c 100644
--- a/crawl-ref/source/effects.cc
+++ b/crawl-ref/source/effects.cc
@@ -4853,18 +4853,16 @@ static void _recharge_rod( item_def &rod, long aut, bool in_inv )
     if (!item_is_rod(rod) || rod.plus >= rod.plus2)
         return;
 
-    const int charge = rod.plus / ROD_CHARGE_MULT;
-
-    int rate = ((charge + 1) * ROD_CHARGE_MULT) / 10;
+    long rate = 4 + short(rod.props["rod_enchantment"]);
 
     rate *= (10 + skill_bump( SK_EVOCATIONS ));
+    rate *= aut;
     rate = div_rand_round( rate, 100 );
-    rate = div_rand_round( rate * aut, 10 );
 
-    if (rate < 5)
-        rate = 5;
-    else if (rate > ROD_CHARGE_MULT / 2)
-        rate = ROD_CHARGE_MULT / 2;
+    if (rate > rod.plus2 - rod.plus) // Prevent overflow
+        rate = rod.plus2 - rod.plus;
+
+    // With this, a +0 rod with no skill gets 1 mana per 25.0 turns
 
     if (rod.plus / ROD_CHARGE_MULT != (rod.plus + rate) / ROD_CHARGE_MULT)
     {
@@ -4873,8 +4871,6 @@ static void _recharge_rod( item_def &rod, long aut, bool in_inv )
     }
 
     rod.plus += rate;
-    if (rod.plus > rod.plus2)
-        rod.plus = rod.plus2;
 
     if (in_inv && rod.plus == rod.plus2)
     {
diff --git a/crawl-ref/source/itemname.cc b/crawl-ref/source/itemname.cc
index d39e16abf2..81bb850f16 100644
--- a/crawl-ref/source/itemname.cc
+++ b/crawl-ref/source/itemname.cc
@@ -1618,7 +1618,17 @@ std::string item_def::name_aux(description_level_type desc,
         }
         else
         {
-            buff << (item_is_rod(*this) ? "rod" : "staff")
+            if (item_is_rod(*this) && know_type && know_pluses
+                && !basename && !qualname && !dbname)
+            {
+                short rmod = 0;
+                if (props.exists("rod_enchantment"))
+                    rmod = props["rod_enchantment"];
+
+                output_with_sign(buff, rmod);
+            }
+
+            buff << (item_is_rod(*this) ? " rod" : " staff")
                  << " of " << staff_type_name(item_typ);
         }
         break;
diff --git a/crawl-ref/source/makeitem.cc b/crawl-ref/source/makeitem.cc
index 7e991e5c83..5f78853508 100644
--- a/crawl-ref/source/makeitem.cc
+++ b/crawl-ref/source/makeitem.cc
@@ -3275,19 +3275,42 @@ int items(int allow_uniques,       // not just true-false,
     return (p);
 }
 
+// Formula from Eronarn on ##crawl-dev; subject to revision
+static int _roll_rod_enchant()
+{
+    int total_prob = 0, cur_ench = 0;
+
+    for (int i = -3; i <= 9; ++i)
+    {
+        int extremeness = (i < 0) ? (21 - i) : (15 + i);
+
+        int prob = 600 - extremeness * extremeness;
+
+        if (random2(total_prob += prob) < prob)
+            cur_ench = i;
+    }
+
+    return cur_ench;
+}
+
 void init_rod_mp(item_def &item, int ncharges)
 {
     if (!item_is_rod(item))
         return;
 
     if (ncharges != -1)
+    {
         item.plus2 = ncharges * ROD_CHARGE_MULT;
+        item.props["rod_enchantment"] = (short)0;
+    }
     else
     {
         if (item.sub_type == STAFF_STRIKING)
             item.plus2 = random_range(6, 9) * ROD_CHARGE_MULT;
         else
             item.plus2 = random_range(9, 14) * ROD_CHARGE_MULT;
+
+        item.props["rod_enchantment"] = (short)_roll_rod_enchant();
     }
 
     item.plus = item.plus2;