add a pair of shorthand macros to validate an index into an array

Two variations:

IndexOk(idx, array)       validate that idx is a valid index into the array

IndexOkT(idx, array)      validate that idx is a valid index into the
                          array, excluding the final Terminator element

include/hack.h

@@ -1406,6 +1406,15 @@ typedef uint32_t mmflags_nht;     /* makemon MM_ flags */
 
 /* pick a random entry from array */
 #define ROLL_FROM(array) array[rn2(SIZE(array))]
+/* array with terminator variation */
+/* #define ROLL_FROMT(array) array[rn2(SIZE(array) - 1)] */
+
+/* validate index of array */
+#define IndexOk(idx, array) \
+    ((idx) >= 0 && (idx) < SIZE(array))
+/* array with terminator variation */
+#define IndexOkT(idx, array) \
+    ((idx) >= 0 && (idx) < (SIZE(array) - 1))
 
 #define FEATURE_NOTICE_VER(major, minor, patch)                    \
     (((unsigned long) major << 24) | ((unsigned long) minor << 16) \

src/cmd.c

@@ -4141,7 +4141,7 @@ wiz_display_macros(void)
                  putstr(win, 0, buf);
             }
             /* check against defsyms array subscripts */
-            if (test < 0 || test >= SIZE(defsyms)) {
+            if (!IndexOk(test, defsyms)) {
                 if (!trouble++)
                     putstr(win, 0, display_issues);
                 Sprintf(buf, "glyph_to_cmap(glyph=%d) returns %d"

src/do_name.c

@@ -2591,7 +2591,7 @@ hliquid(
         if (liquidpref && *liquidpref)
             ++count;
         indx = rn2_on_display_rng(count);
-        if (indx < SIZE(hliquids))
+        if (IndexOk(indx, hliquids))
             return hliquids[indx];
     }
     return liquidpref;
@@ -2742,7 +2742,7 @@ lookup_novel(const char *lookname, int *idx)
         }
     }
     /* name not found; if novelidx is already set, override the name */
-    if (idx && *idx >= 0 && *idx < SIZE(sir_Terry_novels))
+    if (idx && IndexOk(*idx, sir_Terry_novels))
         return sir_Terry_novels[*idx];
 
     return (const char *) 0;

src/monmove.c

@@ -1817,7 +1817,7 @@ m_move(register struct monst *mtmp, int after)
          * mfndpos) has no effect for normal attacks, though it lets a
          * confused monster attack you by accident.
          */
-        assert(chi >= 0 && chi < SIZE(info));
+        assert(IndexOk(chi, info));
         if (info[chi] & ALLOW_U) {
             nix = mtmp->mux;
             niy = mtmp->muy;

src/sounds.c

@@ -1767,7 +1767,7 @@ activate_chosen_soundlib(void)
 {
     int idx = gc.chosen_soundlib;
 
-    if (idx < soundlib_nosound || idx >= SIZE(soundlib_choices))
+    if (!IndexOk(idx, soundlib_choices))
         panic("activate_chosen_soundlib: invalid soundlib (%d)", idx);
 
     if (ga.active_soundlib != soundlib_nosound || idx != soundlib_nosound) {
@@ -1784,7 +1784,7 @@ activate_chosen_soundlib(void)
 void
 assign_soundlib(int idx)
 {
-    if (idx < soundlib_nosound || idx >= SIZE(soundlib_choices))
+    if (!IndexOk(idx, soundlib_choices))
         panic("assign_soundlib: invalid soundlib (%d)", idx);
 
     gc.chosen_soundlib
@@ -1854,7 +1854,7 @@ get_soundlib_name(char *dest, int maxlen)
     const char *src;
 
     idx = ga.active_soundlib;
-    if (idx < soundlib_nosound || idx >= SIZE(soundlib_choices))
+    if (!IndexOk(idx, soundlib_choices))
         panic("get_soundlib_name: invalid active_soundlib (%d)", idx);
 
     src = soundlib_choices[idx].sndprocs->soundname;

src/timeout.c

@@ -112,7 +112,7 @@ static const struct propname {
 const char *
 property_by_index(int idx, int *propertynum)
 {
-    if (!(idx >= 0 && idx < SIZE(propertynames) - 1))
+    if (!IndexOkT(idx, propertynames))
         idx = SIZE(propertynames) - 1;
 
     if (propertynum)

src/trap.c

@@ -1283,7 +1283,7 @@ trapeffect_sqky_board(
             }
         } else {
             seetrap(trap);
-            if (trap->tnote >= 0 && trap->tnote < SIZE(tsnds)) {
+            if (IndexOk(trap->tnote, tsnds)) {
                 Soundeffect(tsnds[trap->tnote], 50);
             }
             pline("A board beneath you %s%s%s.",
@@ -1300,7 +1300,7 @@ trapeffect_sqky_board(
         /* stepped on a squeaky board */
         if (in_sight) {
             if (!Deaf) {
-                if (trap->tnote >= 0 && trap->tnote < SIZE(tsnds)) {
+                if (IndexOk(trap->tnote, tsnds)) {
                     Soundeffect(tsnds[trap->tnote], 50);
                 }
                 pline("A board beneath %s squeaks %s loudly.",
@@ -1315,7 +1315,7 @@ trapeffect_sqky_board(
             int range = couldsee(mtmp->mx, mtmp->my) /* 9 or 5 */
                 ? (BOLT_LIM + 1) : (BOLT_LIM - 3);
 
-            if (trap->tnote >= 0 && trap->tnote < SIZE(tsnds)) {
+            if (IndexOk(trap->tnote, tsnds)) {
                 Soundeffect(tsnds[trap->tnote],
                              ((mdistu(mtmp) <= range * range)
                                 ? 40 : 20));