Use a macro for all foo_RES to MR_foo conversions

This makes it easier to understand what is happening in each of those
places, and also much easier to find the places that conversion between
hero and monster resistances happens (since you can now just grep for
"res_to_mr").  I think I got all the instances where the macro should be
used but I'm not 100% sure since there wasn't a single unique term to
search for to find them all.

I replaced the modifications to give_u_to_m_resistances made in the
previous commit, so that it now uses the same macro as other
conversions, since otherwise it would be much harder to find the
complete list of places where conversions between hero and monster
properties happen.

include/monflag.h

@@ -67,6 +67,9 @@ enum ms_sounds {
 #define MR_POISON       0x20 /* resists poison */
 #define MR_ACID         0x40 /* resists acid */
 #define MR_STONE        0x80 /* resists petrification */
+/* NB: the above resistances correspond to the first 8 hero properties in
+   prop_types (FIRE_RES through STONE_RES), which can be converted to their
+   MR_foo equivalents with the macro res_to_mr() defined in prop.h */
 /* other resistances: magic, sickness */
 /* other conveyances: teleport, teleport control, telepathy */
 

include/prop.h

@@ -20,7 +20,10 @@ enum prop_types {
     POISON_RES        =  6,
     ACID_RES          =  7,
     STONE_RES         =  8,
-    /* note: for the first eight properties, MR_xxx == (1 << (xxx_RES - 1)) */
+    /* note: the first eight properties above are equivalent to MR_xxx bits
+     * MR_FIRE through MR_STONE, and can be directly converted to them: */
+#define res_to_mr(r) \
+    ((FIRE_RES <= (r) && (r) <= STONE_RES) ? (uchar) (1 << ((r) - 1)) : 0x00)
     DRAIN_RES         =  9,
     SICK_RES          = 10,
     INVULNERABLE      = 11,

src/mon.c

@@ -1682,33 +1682,28 @@ mon_give_prop(struct monst *mtmp, int prop)
        control or whatever, ignore it. */
     switch (prop) {
     case FIRE_RES:
-        intrinsic = MR_FIRE;
         msg = "%s shivers slightly.";
         break;
     case COLD_RES:
-        intrinsic = MR_COLD;
         msg = "%s looks quite warm.";
         break;
     case SLEEP_RES:
-        intrinsic = MR_SLEEP;
         msg = "%s looks wide awake.";
         break;
     case DISINT_RES:
-        intrinsic = MR_DISINT;
         msg = "%s looks very firm.";
         break;
     case SHOCK_RES:
-        intrinsic = MR_ELEC;
         msg = "%s crackles with static electricity.";
         break;
     case POISON_RES:
-        intrinsic = MR_POISON;
         msg = "%s looks healthy.";
         break;
     default:
         return; /* can't give it */
         break;
     }
+    intrinsic = res_to_mr(prop);
 
     /* Don't give message if it already had this property intrinsically, but
        still do grant the intrinsic if it only had it from mresists.

src/mondata.c

@@ -1498,20 +1498,14 @@ monstunseesu(unsigned long seenres)
 void
 give_u_to_m_resistances(struct monst *mtmp)
 {
-    const struct {
-        int u;
-        unsigned short m;
-    } u_to_m_res[] = {
-        { FIRE_RES, MR_FIRE }, { COLD_RES, MR_COLD },
-        { SLEEP_RES, MR_SLEEP }, { DISINT_RES, MR_DISINT },
-        { SHOCK_RES, MR_ELEC }, { POISON_RES, MR_POISON },
-        { ACID_RES, MR_ACID }, { STONE_RES, MR_STONE },
-    };
-    int i;
+    int intr;
 
-    for (i = 0; i < SIZE(u_to_m_res); i++) {
-        if ((u.uprops[u_to_m_res[i].u].intrinsic & INTRINSIC) != 0L) {
-            mtmp->mintrinsics |= u_to_m_res[i].m;
+    /* convert the hero's current set of intrinsics to their monster
+       equivalents -- FIRE_RES to MR_FIRE, COLD_RES to MR_COLD, etc -- and
+       add each to the mintrinsics field for the given monster */
+    for (intr = FIRE_RES; intr <= STONE_RES; intr++) {
+        if ((u.uprops[intr].intrinsic & INTRINSIC) != 0L) {
+            mtmp->mintrinsics |= (unsigned short) res_to_mr(intr);
         }
     }
 }

src/worn.c

@@ -550,12 +550,7 @@ update_mon_extrinsics(
         case JUMPING:
             break;
         default:
-            /* 1 through 8 correspond to MR_xxx mask values */
-            if (which >= 1 && which <= 8) {
-                /* FIRE,COLD,SLEEP,DISINT,SHOCK,POISON,ACID,STONE */
-                mask = (uchar) (1 << (which - 1));
-                mon->mextrinsics |= (unsigned short) mask;
-            }
+            mon->mextrinsics |= (unsigned short) res_to_mr(which);
             break;
         }
     } else { /* off */
@@ -592,7 +587,7 @@ update_mon_extrinsics(
              * only one pass but a worn alchemy smock will be an
              * alternate source for either of those two resistances.
              */
-            mask = (uchar) (1 << (which - 1));
+            mask = res_to_mr(which);
             for (otmp = mon->minvent; otmp; otmp = otmp->nobj) {
                 if (otmp == obj || !otmp->owornmask)
                     continue;