Display odds for Confusing Touch/Fungus Form

Resolves crawl#383.

Also, seeing these numbers makes me realize I should probably
re-nerf Confusing Touch.

crawl-ref/source/attack.cc

@@ -1749,8 +1749,7 @@ bool attack::apply_damage_brand(const char *what)
             break;
         }
 
-        if (random2(30) < defender->get_hit_dice()
-            || one_chance_in(5)
+        if (!x_chance_in_y(melee_confuse_chance(defender->get_hit_dice()), 100)
             || defender->as_monster()->check_clarity(false))
         {
             break;

crawl-ref/source/directn.cc

@@ -24,6 +24,7 @@
 #include "describe.h"
 #include "dungeon.h"
 #include "english.h"
+#include "fight.h" // melee_confuse_chance
 #include "food.h"
 #include "godabil.h"
 #include "hints.h"
@@ -3010,6 +3011,13 @@ static vector<string> _get_monster_desc_vector(const monster_info& mi)
 
     _append_container(descs, _get_monster_behaviour_vector(mi));
 
+    if (you.duration[DUR_CONFUSING_TOUCH] && !you.weapon()
+        || you.form == TRAN_FUNGUS && !mons_is_unbreathing(mi.type))
+    {
+        descs.emplace_back(make_stringf("confuse odds on hit: %d%%",
+                                        melee_confuse_chance(mi.hd)));
+    }
+
     if (mi.attitude == ATT_FRIENDLY)
         descs.emplace_back("friendly");
     else if (mi.attitude == ATT_GOOD_NEUTRAL)

crawl-ref/source/fight.cc

@@ -51,6 +51,19 @@
 #include "traps.h"
 #include "travel.h"
 
+/**
+ * What are the odds of an HD-checking confusion effect (e.g. Confusing Touch,
+ * Fungus Form, SPWPN_CHAOS maybe) to confuse a monster of the given HD?
+ *
+ * @param HD    The current hit dice (level) of the monster to confuse.
+ * @return      A percentage chance (0-100) of confusing that monster.
+ *              (Except it tops out at 80%.)
+ */
+int melee_confuse_chance(int HD)
+{
+    return 80 * (30 - HD) / 30;
+}
+
 /**
  * Switch from a bad weapon to melee.
  *

crawl-ref/source/fight.h

@@ -34,6 +34,8 @@ int resist_adjust_damage(const actor *defender, beam_type flavour,
 
 int apply_chunked_AC(int dam, int ac);
 
+int melee_confuse_chance(int HD);
+
 bool wielded_weapon_check(item_def *weapon);
 
 stab_type find_stab_type(const actor *attacker,

crawl-ref/source/mon-util.cc

@@ -3340,6 +3340,19 @@ bool mons_is_seeking(const monster& m)
     return m.behaviour == BEH_SEEK;
 }
 
+bool mons_is_unbreathing(monster_type mc)
+{
+    const mon_holy_type holi = mons_class_holiness(mc);
+
+    if (holi & (MH_UNDEAD | MH_NONLIVING | MH_PLANT))
+        return true;
+
+    if (mons_class_is_slime(mc))
+        return true;
+
+    return mons_class_flag(mc, M_UNBREATHING);
+}
+
 // Either running in fear, or trapped and unable to do so (but still wishing to)
 bool mons_is_fleeing(const monster& m)
 {

crawl-ref/source/mon-util.h

@@ -395,6 +395,7 @@ bool mons_is_active_ballisto(const monster& mon);
 bool mons_has_body(const monster& mon);
 bool mons_has_flesh(const monster& mon);
 bool mons_is_abyssal_only(monster_type mc);
+bool mons_is_unbreathing(monster_type mc);
 
 bool herd_monster(const monster& mon);
 

crawl-ref/source/monster.cc

@@ -3733,15 +3733,7 @@ int monster::how_chaotic(bool check_spells_god) const
 
 bool monster::is_unbreathing() const
 {
-    const mon_holy_type holi = holiness();
-
-    if (holi & (MH_UNDEAD | MH_NONLIVING | MH_PLANT))
-        return true;
-
-    if (mons_is_slime(*this))
-        return true;
-
-    return mons_class_flag(type, M_UNBREATHING);
+    return mons_is_unbreathing(type);
 }
 
 bool monster::is_insubstantial() const