From 689e7490eca26cb5991d4682646ff398fc73bce7 Mon Sep 17 00:00:00 2001
From: PatR <rankin@nethack.org>
Date: Mon, 3 Jun 2019 02:36:44 -0700
Subject: [PATCH] extended ball&chain sanity check

Verify that the locations of ball and chain are consistent.
If chain is on floor then ball is on floor or in hero's inventory
else if chain is free then ball is free or in hero's inventory.
When chain is on floor it is under hero or one step away from hero
and when ball is on floor it is on chain or one step away from chain.
---
 src/ball.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/ball.c b/src/ball.c
index 66ad2ffd8..ab1024a9a 100644
--- a/src/ball.c
+++ b/src/ball.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6	ball.c	$NHDT-Date: 1558920171 2019/05/27 01:22:51 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.38 $ */
+/* NetHack 3.6	ball.c	$NHDT-Date: 1559554598 2019/06/03 09:36:38 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.39 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) David Cohrs, 2006. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -853,7 +853,7 @@ drag_down()
 void
 bc_sanity_check()
 {
-    int otyp;
+    int otyp, freeball, freechain;
     const char *onam;
 
     if (Punished && (!uball || !uchain)) {
@@ -867,11 +867,18 @@ bc_sanity_check()
                    (uchain && uball) ? " and " : "",
                    uball ? "iron ball" : "");
     }
-    /* ball is free when swallowed, changing levels, other times? */
+    /* ball is free when swallowed, when changing levels or during air bubble
+       management on Plane of Water (both of which start and end in between
+       sanity checking cycles, so shouldn't be relevant), other times? */
+    freechain = (!uchain || uchain->where == OBJ_FREE);
+    freeball = (!uball || uball->where == OBJ_FREE
+                /* lie to simplify the testing logic */
+                || (freechain && uball->where == OBJ_INVENT));
     if (uball && (uball->otyp != HEAVY_IRON_BALL
                   || (uball->where != OBJ_FLOOR
                       && uball->where != OBJ_INVENT
                       && uball->where != OBJ_FREE)
+                  || (freeball ^ freechain)
                   || (uball->owornmask & W_BALL) == 0L
                   || (uball->owornmask & ~(W_BALL | W_WEAPON)) != 0L)) {
         otyp = uball->otyp;
@@ -883,6 +890,7 @@ bc_sanity_check()
     if (uchain && (uchain->otyp != IRON_CHAIN
                    || (uchain->where != OBJ_FLOOR
                        && uchain->where != OBJ_FREE)
+                   || (freechain ^ freeball)
                    /* [could simplify this to owornmask != W_CHAIN] */
                    || (uchain->owornmask & W_CHAIN) == 0L
                    || (uchain->owornmask & ~W_CHAIN) != 0L)) {
@@ -891,6 +899,25 @@ bc_sanity_check()
         impossible("uchain: type %d (%s), where %d, wornmask=0x%08lx",
                    otyp, onam, uchain->where, uchain->owornmask);
     }
+    if (uball && uchain && !(freeball && freechain)) {
+        int bx, by, cx, cy, bdx, bdy, cdx, cdy;
+
+        /* non-free chain should be under or next to the hero;
+           non-free ball should be on or next to the chain or else carried */
+        cx = uchain->ox, cy = uchain->oy;
+        cdx = cx - u.ux, cdy = cy - u.uy;
+        cdx = abs(cdx), cdy = abs(cdy);
+        if (uball->where == OBJ_INVENT) /* carried(uball) */
+            bx = u.ux, by = u.uy; /* get_obj_location() */
+        else
+            bx = uball->ox, by = uball->oy;
+        bdx = bx - cx, bdy = by - cy;
+        bdx = abs(bdx), bdy = abs(bdy);
+        if (cdx > 1 || cdy > 1 || bdx > 1 || bdy > 1)
+            impossible(
+                     "b&c distance: you@<%d,%d>, chain@<%d,%d>, ball@<%d,%d>",
+                       u.ux, u.uy, cx, cy, bx, by);
+    }
     /* [check bc_order too?] */
 }