From: Torsten Dreyer <Torsten@t3r.de>
Date: Sat, 20 Nov 2010 10:07:24 +0000 (+0100)
Subject: Avoid division by zero in exponential filters
X-Git-Url: https://git.mxchange.org/?a=commitdiff_plain;h=495a23a80a172f4c0fbda3f087d1469f7d5f734b;p=flightgear.git

Avoid division by zero in exponential filters
---

diff --git a/src/Autopilot/digitalfilter.cxx b/src/Autopilot/digitalfilter.cxx
index 57bca13c8..45087a79a 100644
--- a/src/Autopilot/digitalfilter.cxx
+++ b/src/Autopilot/digitalfilter.cxx
@@ -265,9 +265,14 @@ void ExponentialFilterImplementation::initialize( double output )
 double ExponentialFilterImplementation::compute(  double dt, double input )
 {
   input = GainFilterImplementation::compute( dt, input );
+  double tf = _TfInput.get_value();
 
   double output_0;
-  double alpha = 1 / ((_TfInput.get_value()/dt) + 1);
+
+  // avoid negative filter times 
+  // and div by zero if -tf == dt
+
+  double alpha = tf > 0.0 ? 1 / ((tf/dt) + 1) : 1.0;
  
   if(_isSecondOrder) {
     output_0 = alpha * alpha * input +