/* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
   Copyright (c) 2014-2021 The plumed team
   (see the PEOPLE file at the root of the distribution for a list of names)

   See http://www.plumed.org for more information.

   This file is part of plumed, version 2.

   plumed is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   plumed is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with plumed.  If not, see <http://www.gnu.org/licenses/>.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
#ifndef __PLUMED_tools_OpenMP_h
#define __PLUMED_tools_OpenMP_h

#include <vector>

namespace PLMD {

class OpenMP {

public:

/// Set number of threads that can be used by openMP
  static void setNumThreads(const unsigned nt);

/// Get number of threads that can be used by openMP
  static unsigned getNumThreads();

/// Returns a unique thread identification number within the current team
  static unsigned getThreadNum();

/// get cacheline size
  static unsigned getCachelineSize();

/// Get a reasonable number of threads so as to access to an array of size s located at x
  template<typename T>
  static unsigned getGoodNumThreads(const T*x,unsigned s);

/// Get a reasonable number of threads so as to access to vector v;
  template<typename T>
  static unsigned getGoodNumThreads(const std::vector<T> & v);

};

template<typename T>
unsigned OpenMP::getGoodNumThreads(const T*x,unsigned n) {
  unsigned long p=(unsigned long) x;
  (void) p; // this is not to have warnings. notice that the pointer location is not used actually.
// a factor two is necessary since there is no guarantee that x is aligned
// to cache line boundary
  unsigned m=n*sizeof(T)/(2*getCachelineSize());
  unsigned numThreads=getNumThreads();
  if(m>=numThreads) m=numThreads;
  else m=1;
  return m;
}


template<typename T>
unsigned OpenMP::getGoodNumThreads(const std::vector<T> & v) {
  if(v.size()==0) return 1;
  else return getGoodNumThreads(&v[0],v.size());
}


}

#endif
