Vary vampire blood freshness from a fixed 5 to 8-15 turns per corpse.

A vampire could drain a corpse's blood only while it was at most 5
turns old (ice-adjusted). Widen and randomize that window to 8-15
turns, varying per corpse, so blood freshness is less predictable.

The window is keyed to the corpse's o_id rather than rolled on each
check. A "coagulated" result returns 3 from eatcorpse(), which makes
doeat() return 0 without consuming a turn, so a per-attempt rn1() roll
could be re-rolled for free by re-issuing the eat command until it
landed on 15. A stable o_id-derived value cannot be re-rolled, is
unpredictable to the player, and stays identical across the player
drink, resume, and pet appetite checks.

* mkobj.c: add blood_freshness(), returning 8 + (o_id % 8) turns
  beside peek_at_iced_corpse_age().

* eat.c: route the initial drain gate in eatcorpse() and the
  resume-drain gate in doeat() through blood_freshness() instead of
  the literal 5.

* dog.c: route the tame vampire pet's blood-corpse appetite check
  through blood_freshness() so it agrees with the player's window.

* extern.h: declare blood_freshness().

Author: k21971

doc/evilhack-changelog.md

@@ -5492,4 +5492,5 @@ The following changes to date are:
 - Fix: prevent revived or animated monsters from keeping a steed link
 - Allow players to recover post-crash emergency saves
 - Fix: prevent animated statues from spawning a fresh steed
+- Vary vampire blood freshness from a fixed 5 to 8-15 turns per corpse
 

include/extern.h

@@ -1543,6 +1543,7 @@ E void FDECL(add_to_buried, (struct obj *));
 E void FDECL(dealloc_obj, (struct obj *));
 E void FDECL(obj_ice_effects, (int, int, BOOLEAN_P));
 E long FDECL(peek_at_iced_corpse_age, (struct obj *));
+E long FDECL(blood_freshness, (struct obj *));
 E int FDECL(hornoplenty, (struct obj *, BOOLEAN_P, struct obj *));
 E void NDECL(obj_sanity_check);
 E struct obj *FDECL(obj_nexto, (struct obj *));

src/dog.c

@@ -1292,7 +1292,8 @@ struct obj *obj;
                  && has_blood(&safe_mons(obj->corpsenm))
                  && (!obj->odrained
                      || obj->oeaten > (unsigned) drain_level(obj))
-                 && peek_at_iced_corpse_age(obj) + 5 >= monstermoves);
+                 && peek_at_iced_corpse_age(obj)
+                        + blood_freshness(obj) >= monstermoves);
 
             if (!blood_corpse)
                 return TABU;

src/eat.c

@@ -2051,7 +2051,8 @@ struct obj *otmp;
             return 3;
         } else if (mnum == PM_LIZARD /* lizards don't rot */
                    || (rotted <= 0L
-                       && (peek_at_iced_corpse_age(otmp) + 5) >= monstermoves)) {
+                       && (peek_at_iced_corpse_age(otmp)
+                           + blood_freshness(otmp)) >= monstermoves)) {
             char *buf = corpse_xname(otmp, (const char *) 0, CXN_PFX_THE);
 
             You("drain the blood from %s.", buf);
@@ -3355,8 +3356,8 @@ doeat()
         context.victual.piece = (struct obj *) 0; /* can't resume */
 
     if ((otmp == context.victual.piece) && otmp->odrained
-        && (peek_at_iced_corpse_age(otmp)
-            + context.victual.usedtime + 5) < monstermoves)
+        && (peek_at_iced_corpse_age(otmp) + context.victual.usedtime
+            + blood_freshness(otmp)) < monstermoves)
         context.victual.piece = (struct obj *) 0; /* can't resume */
 
     if (otmp == context.victual.piece) {

src/mkobj.c

@@ -2366,6 +2366,20 @@ struct obj *otmp;
     return retval;
 }
 
+/*
+ * Number of turns a corpse's blood stays drinkable for a vampire after
+ * death (ice-adjusted age). Varies 8..15 per corpse, keyed to the
+ * object's o_id so the window is stable across repeated checks and
+ * identical for the player and a vampire pet -- it cannot be re-rolled
+ * by retrying the attempt.
+ */
+long
+blood_freshness(otmp)
+struct obj *otmp;
+{
+    return 8L + (long) (otmp->o_id % 8);
+}
+
 STATIC_OVL void
 obj_timer_checks(otmp, x, y, force)
 struct obj *otmp;