phihelper.h

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/*
  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
*/
#ifndef CXXUTILS_PHIHELPER_H
#define CXXUTILS_PHIHELPER_H
 
#include <cmath>
#include <type_traits>
 
namespace CxxUtils {

  template <typename T>
  inline T wrapToPi(T phi)
  {
    static_assert(std::is_floating_point<T>::value);
 
    constexpr auto PI = static_cast<T>(M_PI);
    // For large values this is faster:
    if (phi < -100 || phi > 100) {
      return std::remainder(phi, 2 * PI);
    }
    while (phi > PI) phi -= 2 * PI;
    while (phi < -PI) phi += 2 * PI;
    return phi;
  }

  template <typename T>
  inline T deltaPhi(T phiA, T phiB)
  {
    static_assert(std::is_floating_point<T>::value);
    return wrapToPi(phiA - phiB);
  }

  template <typename T>
  inline T phiMean(T phiA, T phiB)
  {
    static_assert(std::is_floating_point<T>::value);
    const T diff = wrapToPi(phiA - phiB);
    return wrapToPi(phiB + 0.5 * diff);
  }

  template <typename T>
  inline T phiBisect(T phiA, T phiB)
  {
    static_assert(std::is_floating_point<T>::value);
    T phi = 0.5 * (phiA + phiB);
    if (phiA > phiB) phi += M_PI;
    return wrapToPi(phi);
  }
 
} // namespace CxxUtils
 
#endif