RandomRing.h

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
 
 
 
#ifndef ALICEO2_MATHUTILS_RANDOMRING_H_
#define ALICEO2_MATHUTILS_RANDOMRING_H_
 
#include <array>
 
#include "TF1.h"
#include "TRandom.h"
#include <functional>
 
 
namespace o2
{
namespace math_utils
{
 
template <size_t N = 4 * 100000>
class RandomRing
{
 public:
  enum class RandomType : char {
    Gaus,         
    Flat,         
    CustomTF1,    
    CustomLambda, 
  };
 
  RandomRing(const RandomType randomType = RandomType::Gaus, TRandom* rng = nullptr);
 
  RandomRing(TF1& function);
 
  void initialize(const RandomType randomType = RandomType::Gaus, TRandom* rng = nullptr);
 
  void initialize(TF1& function, TRandom* rng = nullptr);
 
  void initialize(std::function<float()> function);
 
  float getNextValue()
  {
    const float value = mRandomNumbers[mRingPosition];
    ++mRingPosition;
    if (mRingPosition >= mRandomNumbers.size()) {
      mRingPosition = 0;
    }
    return value;
  }
 
  template <typename VcType>
  VcType getNextValueVc()
  {
    // This function is templated so that we don't need to include the <Vc/Vc> header
    // within this header file (to reduce memory problems during compilation).
    // The hope is that the calling user calls this with a
    // correct Vc type (Vc::float_v) in a source file.
    // a vector must not run past the end of the ring, also after setRandomPosition()
    if (mRingPosition + VcType::size() > mRandomNumbers.size()) {
      mRingPosition = 0;
    }
    const VcType value = VcType(&mRandomNumbers[mRingPosition]);
    mRingPosition += VcType::size();
    if (mRingPosition >= mRandomNumbers.size()) {
      mRingPosition = 0;
    }
    return value;
  }
 
  unsigned int getRingPosition() const { return mRingPosition; }
 
  void setRandomPosition(TRandom& rng) { mRingPosition = rng.Integer(N); }
 
 private:
  // =========================================================================
  // ===| members |===========================================================
  //
 
  RandomType mRandomType;              
  std::array<float, N> mRandomNumbers; 
  size_t mRingPosition = 0;            
 
}; // end class RandomRing
 
//______________________________________________________________________________
template <size_t N>
inline RandomRing<N>::RandomRing(const RandomType randomType, TRandom* rng)
  : mRandomType(randomType),
    mRandomNumbers()
 
{
  initialize(randomType, rng);
}
 
//______________________________________________________________________________
template <size_t N>
inline RandomRing<N>::RandomRing(TF1& function)
  : mRandomType(RandomType::CustomTF1),
    mRandomNumbers()
{
  initialize(function);
}
 
//______________________________________________________________________________
template <size_t N>
inline void RandomRing<N>::initialize(const RandomType randomType, TRandom* rng)
{
  TRandom* random = rng ? rng : gRandom;
  for (auto& v : mRandomNumbers) {
    // TODO: configurable mean and sigma
    switch (randomType) {
      case RandomType::Gaus: {
        v = random->Gaus(0, 1);
        break;
      }
      case RandomType::Flat: {
        v = random->Rndm();
        break;
      }
      default: {
        v = 0;
        break;
      }
    }
  }
}
 
//______________________________________________________________________________
template <size_t N>
inline void RandomRing<N>::initialize(TF1& function, TRandom* rng)
{
  mRandomType = RandomType::CustomTF1;
  for (auto& v : mRandomNumbers) {
    v = function.GetRandom(rng);
  }
}
 
//______________________________________________________________________________
template <size_t N>
inline void RandomRing<N>::initialize(std::function<float()> function)
{
  mRandomType = RandomType::CustomLambda;
  for (auto& v : mRandomNumbers) {
    v = function();
  }
}
 
} // namespace math_utils
} // namespace o2
#endif