Make ComputeAngle a free standing function

include/util/compute_angle.hpp

@@ -1,21 +1,36 @@
 #ifndef COMPUTE_ANGLE_HPP
 #define COMPUTE_ANGLE_HPP
 
+#include "osrm/coordinate.hpp"
+#include "util/trigonometry_table.hpp"
+#include "util/mercator.hpp"
+
 namespace osrm
 {
 namespace util
 {
 
-struct FixedPointCoordinate;
-
-struct ComputeAngle
+// Get angle of line segment (A,C)->(C,B)
+inline double ComputeAngle(const FixedPointCoordinate first,
+                           const FixedPointCoordinate second,
+                           const FixedPointCoordinate third) noexcept
 {
-    // Get angle of line segment (A,C)->(C,B)
-    // atan2 magic, formerly cosine theorem
-    static double OfThreeFixedPointCoordinates(const FixedPointCoordinate &first,
-                                               const FixedPointCoordinate &second,
-                                               const FixedPointCoordinate &third) noexcept;
-};
+    const double v1x = (first.lon - second.lon) / COORDINATE_PRECISION;
+    const double v1y = mercator::lat2y(first.lat / COORDINATE_PRECISION) -
+                       mercator::lat2y(second.lat / COORDINATE_PRECISION);
+    const double v2x = (third.lon - second.lon) / COORDINATE_PRECISION;
+    const double v2y = mercator::lat2y(third.lat / COORDINATE_PRECISION) -
+                       mercator::lat2y(second.lat / COORDINATE_PRECISION);
+
+    double angle = (atan2_lookup(v2y, v2x) - atan2_lookup(v1y, v1x)) * 180. / M_PI;
+
+    while (angle < 0.)
+    {
+        angle += 360.;
+    }
+
+    return angle;
+}
 }
 }