utility.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2018 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library 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 2.1 of the License, or (at your option) any later version.

// This library 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 this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA


#ifndef LIBMESH_UTILITY_H
#define LIBMESH_UTILITY_H

// Local includes
#include "libmesh/libmesh_common.h" // for Real

// System includes
#include <string>
#include <vector>
#include <algorithm> // for std::lower_bound

namespace libMesh
{


// ------------------------------------------------------------
// The Utility namespace is for functions
// which are useful but don't necessarily belong anywhere else.

namespace Utility
{

std::string system_info();



template <typename ForwardIter, typename T>
void iota (ForwardIter first, ForwardIter last, T value)
{
  // Use std::iota instead!
  libmesh_deprecated();

  while (first != last)
    {
      *first = value++;
      ++first;
    }
}


template<class InputIterator >
bool is_sorted(InputIterator first, InputIterator last)
{
  if (first == last)
    return true;

  // "prev" always points to the entry just to the left of "first"
  //  [-    -    -    -    -    -]
  //   ^    ^
  // prev first
  //
  //  [-    -    -    -    -    -]
  //        ^    ^
  //      prev first
  //
  //  [-    -    -    -    -    -]
  //             ^    ^
  //           prev first
  InputIterator prev( first );
  for (++first; first != last; ++prev, ++first)
    if (*first < *prev)    // Note: this is the same as *prev > *first,
      return false;        // but we only require op< to be defined.

  // If we haven't returned yet, it's sorted!
  return true;


  // A one-liner version using adjacent_find.  This doesn't work for
  // C-style arrays, since their pointers do not have a value_type.
  //
  // Works by checking to see if adjacent entries satisfy *i >
  // *(i+1) and returns the first one which does.  If "last" is
  // returned, no such pair was found, and therefore the range must
  // be in non-decreasing order.
  //
  // return (last ==
  // std::adjacent_find(first, last,
  // std::greater<typename InputIterator::value_type >()));

  // A second one-linear attempt.  This one checks for a **strictly
  // increasing** (no duplicate entries) range.  Also doesn't work
  // with C-style arrays.
  //
  // return (last ==
  // std::adjacent_find(first, last,
  // std::not2(std::less<typename InputIterator::value_type>())));
}


template<class ForwardIterator, class T>
ForwardIterator binary_find(ForwardIterator first, ForwardIterator last, const T & value)
{
  ForwardIterator it = std::lower_bound(first, last, value);
  return (it == last || value < *it) ? last : it;
}

template<class ForwardIterator, class T, class Compare>
ForwardIterator binary_find(ForwardIterator first, ForwardIterator last, const T & value, Compare comp)
{
  ForwardIterator it = std::lower_bound(first, last, value, comp);
  return (it == last || comp(value,*it)) ? last : it;
}


template <int N, typename T>
struct do_pow {
  static inline T apply (const T & x)
  {
    libmesh_assert(N>1);

    if (N%2) // odd exponent
      return x * do_pow<N-1,T>::apply(x);

    const T xNover2 = do_pow<N/2,T>::apply(x);

    return xNover2*xNover2;
  }
};

// An efficient compiler would distill N=6 down to 3
// multiplications, but an inefficient one (or a complicated
// T::operator*) might do worse, so we'll specialize here.
template <typename T>
struct do_pow<6,T> {
  static inline T apply (const T & x)
  {
    const T x2 = x*x,
      x4 = x2*x2;

    return x4*x2;
  }
};

template <typename T>
struct do_pow<1,T> {
  static inline T apply (const T & x) { return x; }
};

template <typename T>
struct do_pow<0,T> {
  static inline T apply (const T &) { return 1; }
};


template <int N, typename T>
inline
T pow(const T & x)
{
  return do_pow<N,T>::apply(x);
}

inline
unsigned int factorial(unsigned int n)
{

  unsigned int factorial_n = 1;

  if (n==0)
    return factorial_n;

  for (unsigned int i=1; i<n; i++)
    factorial_n *= i+1;

  return factorial_n;
}


// Simple function to compute "n choose k", aka the binomial coefficient.
template <typename T>
T binomial(T n, T k)
{
  T ret = 1;

  // Binomial function is "symmetric" in k, C(n, k) = C(n, n-k).
  if (k > n - k)
    k = n - k;

  // Compute n * (n-1) * ... * (n-k+1) / (k * (k-1) * ... * 1)
  for (T i = 0; i < k; ++i)
    {
      ret *= (n - i);
      ret /= (i + 1);
    }

  return ret;
}


template <typename T>
void deallocate (std::vector<T> & vec)
{
  std::vector<T>().swap(vec);
}


// Utility functions useful when dealing with complex numbers.

#ifdef LIBMESH_USE_COMPLEX_NUMBERS

std::string complex_filename (const std::string & basename,
                              unsigned int r_o_c=0);

void prepare_complex_data (const std::vector<Complex> & source,
                           std::vector<Real> & real_part,
                           std::vector<Real> & imag_part);

#endif // #ifdef LIBMESH_USE_COMPLEX_NUMBERS


int mkdir(const char* pathname);


class ReverseBytes
{
public:

  explicit
  ReverseBytes (const bool dr);

  template <typename T>
  T operator () (T & data) const;

private:

  bool reverse () const { return _do_reverse; }

  const bool _do_reverse;
};



// ReverseBytes inline members
inline
ReverseBytes::ReverseBytes (const bool rb) :
  _do_reverse (rb)
{}


template <typename T>
inline
T ReverseBytes::operator() (T & data) const
{
  // Possibly reverse the byte ordering
  if (this->reverse())
    {
      unsigned char * b = (unsigned char *) &data;

      int i=0;
      int j=(sizeof(T) - 1);

      while (i < j)
        {
          std::swap (b[i], b[j]);
          i++; j--;
        }
    }

  return data;
}


}

} // namespace libMesh

#endif // LIBMESH_UTILITY_H