removing piBy180 from critical path (#821)

pkg/routing/selector/regionaware.go

@@ -88,6 +88,8 @@ func hsin(theta float64) float64 {
 	return math.Pow(math.Sin(theta/2), 2)
 }
 
+var piBy180 = math.Pi / 180
+
 // Haversine Distance Formula
 // http://en.wikipedia.org/wiki/Haversine_formula
 // from https://gist.github.com/cdipaolo/d3f8db3848278b49db68
@@ -95,10 +97,10 @@ func distanceBetween(lat1, lon1, lat2, lon2 float64) float64 {
 	// convert to radians
 	// must cast radius as float to multiply later
 	var la1, lo1, la2, lo2, r float64
-	la1 = lat1 * math.Pi / 180
-	lo1 = lon1 * math.Pi / 180
-	la2 = lat2 * math.Pi / 180
-	lo2 = lon2 * math.Pi / 180
+	la1 = lat1 * piBy180
+	lo1 = lon1 * piBy180
+	la2 = lat2 * piBy180
+	lo2 = lon2 * piBy180
 
 	r = 6378100 // Earth radius in METERS