From: PatR <rankin@nethack.org>
Date: Thu, 24 Mar 2022 18:15:37 +0000 (-0700)
Subject: mazexy() again
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=f86ab67d203f6d6a318e28b6ef371b12fffafe9e;p=nethack

mazexy() again

Some maze code treats row y_maze_max and column x_maze_max as being
in play, other parts treat them as out.  mazexy() was doing both; the
first loop to choose a random spot allowed them, the second loop to
try every possible spot disallowed them.  Make those be consistent.

I think the extreme row and column are both expected to be solid wall
so failing to consider them might not be causing any problems.

While in there, change mazexy() to not set cc->{x,y} until it has
found a viable spot instead of potentionally making that assignment
dozens or hundreds of times.  The only difference there is that 'cc'
won't have been assigned any value if panic() gets called.
---

diff --git a/src/mkmaze.c b/src/mkmaze.c
index e85c5616f..da5254cf5 100644
--- a/src/mkmaze.c
+++ b/src/mkmaze.c
@@ -816,7 +816,10 @@ static boolean
 maze_inbounds(int x, int y)
 {
     return (x >= 2 && y >= 2
-            && x < g.x_maze_max && y < g.y_maze_max && isok(x, y));
+            && x < g.x_maze_max && y < g.y_maze_max
+            /* isok() test is superfluous here (unless something has
+               clobbered the static *_maze_max variables) */
+            && isok(x, y));
 }
 
 static void
@@ -1213,28 +1216,36 @@ walkfrom(int x, int y, schar typ)
 void
 mazexy(coord *cc)
 {
+    int x, y, allowedtyp = (g.level.flags.corrmaze ? CORR : ROOM);
     int cpt = 0;
 
     do {
-        cc->x = 1 + rn2(g.x_maze_max);
-        cc->y = 1 + rn2(g.y_maze_max);
-        if (levl[cc->x][cc->y].typ == (g.level.flags.corrmaze ? CORR : ROOM))
+        /* once upon a time this only considered odd values greater than 2
+           and less than N (for N=={x,y}_maze_max) because even values were
+           where maze walls always got placed; when wider maze corridors
+           were introduced it was changed to 1+rn2(N) which is just an
+           obscure way to get rnd(N); probably ought to be using 2+rn2(N-1)
+           to exclude the maze's outer boundary walls; trying and rejecting
+           those walls will waste some of the 100 random attempts... */
+        x = rnd(g.x_maze_max);
+        y = rnd(g.y_maze_max);
+        if (levl[x][y].typ == allowedtyp) {
+            cc->x = (xchar) x;
+            cc->y = (xchar) y;
             return;
+        }
     } while (++cpt < 100);
-
-    if (cpt >= 100) {
-        int x, y;
-
-        /* last try */
-        for (x = 1; x < g.x_maze_max; x++)
-            for (y = 1; y < g.y_maze_max; y++) {
-                cc->x = x;
-                cc->y = y;
-                if (levl[x][y].typ == (g.level.flags.corrmaze ? CORR : ROOM))
-                    return;
+    /* 100 random attempts failed; systematically try every possibility */
+    for (x = 1; x <= g.x_maze_max; x++)
+        for (y = 1; y <= g.y_maze_max; y++)
+            if (levl[x][y].typ == allowedtyp) {
+                cc->x = (xchar) x;
+                cc->y = (xchar) y;
+                return;
             }
-        panic("mazexy: can't find a place!");
-    }
+    /* every spot on the area of map allowed for mazes has been rejected */
+    panic("mazexy: can't find a place!");
+    /*NOTREACHED*/
     return;
 }