Changeset 810 for cpp

Timestamp:

07/27/18 16:21:58 (6 years ago)

Author:

Maciej Komosinski

Message:

Don't unnecessarily calculate sqrt(negative_value) [fixes #51]

File:

• cpp/frams/model/geometry/geometryutils.cpp (modified) (1 diff)

cpp/frams/model/geometry/geometryutils.cpp

@@ -336 +336 @@
 {
         x += d / sqrt(1.0 + (b*b * x*x) / (a*a * (a*a - x*x)));
-        y = b * sqrt(1.0 - (x*x) / (a*a));
+        double sqrt_arg = 1.0 - (x*x) / (a*a);
+        if (sqrt_arg >= 0)
+                y = b * sqrt(sqrt_arg);
+        else
+                y = std::numeric_limits<double>::signaling_NaN();
+        //This function is called from MeshBuilder::EllipsoidSurface::findNextAreaEdgeAndPhase(). 
+        //y=NaN set above co-occurs with the value of x that doesn't meet the condition tested in findNextAreaEdgeAndPhase().
+        //If the condition is true (i.e., x exceeds the allowed range), entirely new values of x and y are set in the next step anyway.
+        //An impossible-to-calculate y should never be used for invalid x, hence y=NaN is set here to indicate this specific situation and signal just in case anyone would try to use such y.
 }