[Common] RecoDecay::constrainAngle: Support harmonics (AliceO2Group#8816)

Author: vkucera

Common/Core/RecoDecay.h

@@ -208,18 +208,23 @@ struct RecoDecay {
   /// Constrains angle to be within a range.
   /// \note Inspired by TVector2::Phi_0_2pi in ROOT.
   /// \param angle  angle
-  /// \param min  minimum of the range
-  /// \return value within [min, min + 2π).
+  /// \param minimum  minimum of the range
+  /// \param harmonic  harmonic number
+  /// \return value of angle within [minimum, minimum + 2π / harmonic).
   template <typename T, typename U = float>
-  static T constrainAngle(T angle, U min = 0.)
+  static T constrainAngle(T angle, U minimum = 0.0F, unsigned int harmonic = 1U)
   {
-    while (angle < min) {
-      angle += o2::constants::math::TwoPI;
+    auto period = o2::constants::math::TwoPI;
+    if (harmonic != 1U) {
+      period /= harmonic;
     }
-    while (angle >= min + o2::constants::math::TwoPI) {
-      angle -= o2::constants::math::TwoPI;
+    while (angle < minimum) {
+      angle += period;
     }
-    return (T)angle;
+    while (angle >= minimum + period) {
+      angle -= period;
+    }
+    return angle;
   }
 
   /// Calculates cosine of pointing angle.