From 01d6408def7d1f5153180c206364abec7fe20dcf Mon Sep 17 00:00:00 2001
From: curt <curt>
Date: Fri, 4 Dec 1998 01:25:05 +0000
Subject: [PATCH] math domain error fix from Charlie Hotchkiss.

---
 Astro/celestialBody.cxx | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/Astro/celestialBody.cxx b/Astro/celestialBody.cxx
index 72bb6359a..35b01e244 100644
--- a/Astro/celestialBody.cxx
+++ b/Astro/celestialBody.cxx
@@ -27,7 +27,7 @@
 #include "star.hxx"
 #include <Debug/logstream.hxx>
 
-#ifdef __BORLANDC__
+#ifdef FG_MATH_EXCEPTION_CLASH
 #  define exception c_exception
 #endif
 #include <math.h>
@@ -90,7 +90,19 @@ void CelestialBody::updatePosition(fgTIME *t, Star *ourSun)
   //of the planet
   R = sqrt (xg*xg + yg*yg + zg*zg);
   s = ourSun->getDistance();
-  FV = RAD_TO_DEG * acos( (r*r + R*R - s*s) / (2*r*R));
+
+  // It is possible from these calculations for the argument to acos
+  // to exceed the valid range for acos(). So we do a little extra
+  // checking.
+
+  double tmp = (r*r + R*R - s*s) / (2*r*R);
+  if ( tmp > 1.0) { 
+      tmp = 1.0;
+  } else if ( tmp < -1.0) {
+      tmp = -1.0;
+  }
+
+  FV = RAD_TO_DEG * acos( tmp );
 };
 
 /****************************************************************************
-- 
2.39.5