ENH: consistency improvement for edge/line

- added line::last() for consistency with edge::last()

- adjusted unitVec() to return Zero for small vectors.
  Consistent with VectorSpace normalised() and vector::normalise()

src/OpenFOAM/meshes/meshShapes/edge/edgeI.H

@@ -421,10 +421,10 @@ inline Foam::vector Foam::edge::unitVec(const UList<point>& pts) const
     }
     #endif
 
-    Foam::vector v = pts[second()] - pts[first()];
-    v /= ::Foam::mag(v) + VSMALL;
+    const vector v = (pts[second()] - pts[first()]);
+    const scalar s(Foam::mag(v));
 
-    return v;
+    return s < ROOTVSMALL ? Zero : v/s;
 }
 
 

src/OpenFOAM/meshes/primitiveShapes/line/line.H

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2018 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -98,20 +98,23 @@ public:
         inline line(Istream&);
 
 
-    // Member functions
+    // Member Functions
 
     // Access
 
         //- Return first point
         inline PointRef first() const;
 
-        //- Return second point
+        //- Return second (last) point
         inline PointRef second() const;
 
+        //- Return last (second) point
+        inline PointRef last() const;
+
         //- Return first point
         inline PointRef start() const;
 
-        //- Return second point
+        //- Return second (last) point
         inline PointRef end() const;
 
 

src/OpenFOAM/meshes/primitiveShapes/line/lineI.H

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011 OpenFOAM Foundation
-     \\/     M anipulation  |
+     \\/     M anipulation  | Copyright (C) 2018 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -23,6 +23,7 @@ License
 
 \*---------------------------------------------------------------------------*/
 
+#include "zero.H"
 #include "IOstreams.H"
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
@@ -70,6 +71,13 @@ inline PointRef Foam::line<Point, PointRef>::second() const
 }
 
 
+template<class Point, class PointRef>
+inline PointRef Foam::line<Point, PointRef>::last() const
+{
+    return b_;
+}
+
+
 template<class Point, class PointRef>
 inline PointRef Foam::line<Point, PointRef>::start() const
 {
@@ -107,10 +115,10 @@ inline Point Foam::line<Point, PointRef>::vec() const
 template<class Point, class PointRef>
 inline Point Foam::line<Point, PointRef>::unitVec() const
 {
-    Point v = b_ - a_;
-    v /= ::Foam::mag(v) + VSMALL;
+    const Point v = (b_ - a_);
+    const scalar s(::Foam::mag(v));
 
-    return v;
+    return s < ROOTVSMALL ? Zero : v/s;
 }