worm segment placement

random_dir() for picking a spot to put a segment of a long worm's tail
(when it is being placed on the map, perhaps after teleport, not when
movement allows it to grow) had mistakes in three of the four compass
directions.  The one for the top of the map was benign; it just
neglected to use the top row (#0).  But it could pick a value off the
edge of the map for bottom and right or both.

This doesn't explain a couple of long worm [segment] oddities on the
Astral level because that level doesn't go all the way to the edge.

diff --git a/src/worm.c b/src/worm.c
index 80d64449937b347bc8e917441b81f6ed0b337225..1d7dd8ad2b30cc9db684c6372aee93e75e9523dd 100644 (file)
--- a/src/worm.c
+++ b/src/worm.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6 worm.c  $NHDT-Date: 1543892216 2018/12/04 02:56:56 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.28 $ */
+/* NetHack 3.6 worm.c  $NHDT-Date: 1561340880 2019/06/24 01:48:00 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.30 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2009. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -669,7 +669,6 @@ xchar x, y;
         char tryct = 0;
 
         /* pick a random direction from x, y and search for goodpos() */
-
         do {
             random_dir(ox, oy, &nx, &ny);
         } while (!goodpos(nx, ny, worm, 0) && (tryct++ < 50));
@@ -700,21 +699,26 @@ xchar x, y;
 STATIC_OVL
 void
 random_dir(x, y, nx, ny)
-register xchar x, y;
-register xchar *nx, *ny;
+xchar x, y;
+xchar *nx, *ny;
 {
-    *nx = x;
-    *ny = y;
-
-    *nx += (x > 1                     /* extreme left ? */
-              ? (x < COLNO            /* extreme right ? */
-                   ? (rn2(3) - 1)     /* neither so +1, 0, or -1 */
-                   : -rn2(2))         /* 0, or -1 */
-              : rn2(2));              /* 0, or 1 */
-
-    *ny += (*nx == x                  /* same kind of thing with y */
-              ? (y > 1 ? (y < ROWNO ? (rn2(2) ? 1 : -1) : -1) : 1)
-              : (y > 1 ? (y < ROWNO ? (rn2(3) - 1) : -rn2(2)) : rn2(2)));
+    *nx = x + (x > 1                /* extreme left ? */
+               ? (x < COLNO - 1     /* extreme right ? */
+                  ? (rn2(3) - 1)    /* neither so +1, 0, or -1 */
+                  : -rn2(2))        /* right edge, use -1 or 0 */
+               : rn2(2));           /* left edge, use 0 or 1 */
+    if (*nx != x) /* if x has changed, do same thing with y */
+        *ny = y + (y > 0             /* y==0 is ok (x==0 is not) */
+                   ? (y < ROWNO - 1
+                      ? (rn2(3) - 1)
+                      : -rn2(2))
+                   : rn2(2));
+    else /* when x has remained the same, force y to change */
+        *ny = y + (y > 0
+                   ? (y < ROWNO - 1
+                      ? (rn2(2) ? 1 : -1)   /* not at edge, so +1 or -1 */
+                      : -1)                 /* bottom, use -1 */
+                   : 1);                    /* top, use +1 */
 }
 
 /* for size_monst(cmd.c) to support #stats */