From 308b928f8c653d185369da6faa094b74131d2180 Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver@mutability.co.uk>
Date: Fri, 26 Aug 2016 11:31:32 +0100
Subject: [PATCH] If maxrange is 0, we cannot do receiver-relative CPR at all.

---
 track.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/track.c b/track.c
index 79e89a9..2be134b 100644
--- a/track.c
+++ b/track.c
@@ -308,7 +308,9 @@ static int doLocalCPR(struct aircraft *a, struct modesMessage *mm, uint64_t now,
         // at 200NM distance, this may resolve to a position
         // at (200-360) = 160NM in the wrong direction)
 
-        if (Modes.maxRange <= 1852*180) {
+        if (Modes.maxRange == 0) {
+            return (-1); // Can't do receiver-centered checks at all
+        } else if (Modes.maxRange <= 1852*180) {
             range_limit = Modes.maxRange;
         } else if (Modes.maxRange < 1852*360) {
             range_limit = (1852*360) - Modes.maxRange;