fix pull request #365 - monster max HP

The recently added sanity check for monster maximum HP was giving
false complaints when Nd8 monster had N mhpmax.  Most noticeable
for level 1 monsters (level 0 monsters use 1d4 instead of 0d8 and
weren't affected) but possible for higher level ones if they were
unlucky--from their own perspective--with all their d8 rolls.

Give level N monsters a minimum of N+1 HP, so minimum of 2 for
level 1 monsters, making 1/8 of those stronger.  Same minimum for
level 0 monsters, 25% of which will become stronger now.  (The pull
request's patch gave every Nd8 monster 1 extra HP; this only does
so for Nd8 and 1d4 ones which have rolled lowest possible amount.)

Also relax the sanity check so that existing to-be-3.7 save files
don't continue to trigger sanity complaints for existing monsters
that have the old minimum.

Fixes 365

doc/fixes37.0

@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.248 $ $NHDT-Date: 1594730609 2020/07/14 12:43:29 $
+$NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.249 $ $NHDT-Date: 1594771373 2020/07/15 00:02:53 $
 
 General Fixes and Modified Features
 -----------------------------------
@@ -287,6 +287,8 @@ only generate shop items on solid floor squares
 avoid gcc 10 warning by removing duplicate definition of 'head_engr'
 if a monster removed a corpse from an ice box, the corpse would never rot away
 monster creation on quest levels could make genocided creatures
+enabling wizard mode 'sanity_check' option would complain about invalid mhpmax
+	value for level N monsters created with a d8 value of 1 for all N d8's
 
 tty: redraw unexplored locations as S_unexplored rather than <space> after
 	map has been partially overwritten by popup menu or text display

src/makemon.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	makemon.c	$NHDT-Date: 1591178397 2020/06/03 09:59:57 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.173 $ */
+/* NetHack 3.6	makemon.c	$NHDT-Date: 1594771378 2020/07/15 00:02:58 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.174 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2012. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -997,13 +997,16 @@ struct monst *mon;
 int mndx;
 {
     struct permonst *ptr = &mons[mndx];
+    int basehp = 0;
 
     mon->m_lev = adj_lev(ptr);
     if (is_golem(ptr)) {
+        /* golems have a fixed amount of HP, varying by golem type */
         mon->mhpmax = mon->mhp = golemhp(mndx);
     } else if (is_rider(ptr)) {
         /* we want low HP, but a high mlevel so they can attack well */
-        mon->mhpmax = mon->mhp = d(10, 8);
+        basehp = 10; /* minimum is 1 per false (weaker) level */
+        mon->mhpmax = mon->mhp = d(basehp, 8);
     } else if (ptr->mlevel > 49) {
         /* "special" fixed hp monster
          * the hit points are encoded in the mlevel in a somewhat strange
@@ -1012,17 +1015,26 @@ int mndx;
         mon->mhpmax = mon->mhp = 2 * (ptr->mlevel - 6);
         mon->m_lev = mon->mhp / 4; /* approximation */
     } else if (ptr->mlet == S_DRAGON && mndx >= PM_GRAY_DRAGON) {
-        /* adult dragons */
+        /* adult dragons; N*(4+rnd(4)) before endgame, N*8 once there */
-        mon->mhpmax = mon->mhp =
+        basehp = (int) mon->m_lev; /* not really applicable; isolates cast */
-            (int) (In_endgame(&u.uz)
+        mon->mhpmax = mon->mhp = In_endgame(&u.uz) ? (8 * basehp)
-                       ? (8 * mon->m_lev)
+                                 : (4 * basehp + d(basehp, 4));
-                       : (4 * mon->m_lev + d((int) mon->m_lev, 4)));
     } else if (!mon->m_lev) {
+        basehp = 1; /* minimum is 1, increased to 2 below */
         mon->mhpmax = mon->mhp = rnd(4);
     } else {
-        mon->mhpmax = mon->mhp = d((int) mon->m_lev, 8);
+        basehp = (int) mon->m_lev; /* minimum possible is one per level */
+        mon->mhpmax = mon->mhp = d(basehp, 8);
         if (is_home_elemental(ptr))
-            mon->mhpmax = (mon->mhp *= 3);
+            mon->mhpmax = (mon->mhp *= 3); /* leave 'basehp' as-is */
+    }
+
+    /* if d(X,8) rolled a 1 all X times, give a boost;
+       most beneficial for level 0 and level 1 monsters, making mhpmax
+       and starting mhp always be at least 2 */
+    if (mon->mhpmax == basehp) {
+        mon->mhpmax += 1;
+        mon->mhp = mon->mhpmax;
     }
 }
 

src/mon.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	mon.c	$NHDT-Date: 1594727746 2020/07/14 11:55:46 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.340 $ */
+/* NetHack 3.6	mon.c	$NHDT-Date: 1594771374 2020/07/15 00:02:54 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.341 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Derek S. Ray, 2015. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -59,7 +59,7 @@ const char *msg;
         /* check before DEADMONSTER() because dead monsters should still
            have sane mhpmax */
         if (mtmp->mhpmax < 1
-            || mtmp->mhpmax < (int) mtmp->m_lev + 1
+            || mtmp->mhpmax < (int) mtmp->m_lev
             || mtmp->mhp > mtmp->mhpmax)
             impossible(
                      "%s: level %d monster #%u [%s] has %d cur HP, %d max HP",