spatial/r{2,3}: add Norm and Norm2

spatial/r2/vector.go

@@ -4,6 +4,8 @@
 
 package r2
 
+import "math"
+
 // Vec is a 2D vector.
 type Vec struct {
 	X, Y float64
@@ -40,6 +42,18 @@ func (p Vec) Cross(q Vec) float64 {
 	return p.X*q.Y - p.Y*q.X
 }
 
+// Norm returns the Euclidean norm of p
+//  |p| = sqrt(p_x^2 + p_y^2).
+func Norm(p Vec) float64 {
+	return math.Hypot(p.X, p.Y)
+}
+
+// Norm returns the Euclidean squared norm of p
+//  |p|^2 = p_x^2 + p_y^2.
+func Norm2(p Vec) float64 {
+	return p.X*p.X + p.Y*p.Y
+}
+
 // Box is a 2D bounding box.
 type Box struct {
 	Min, Max Vec