utility.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2026 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
 
// LibMesh includes
#include "libmesh/libmesh_common.h" // for Real
 
// C++ includes
#include <string>
#include <vector>
#include <algorithm> // is_sorted, lower_bound
#include <memory> // unique_ptr
 
namespace libMesh
{
 
#define libmesh_map_find(map, key) libMesh::Utility::map_find((map), (key), __FILE__, __LINE__)
 
#define libmesh_vector_at(vec, idx) libMesh::Utility::vector_at((vec), (idx), __FILE__, __LINE__)
 
// ------------------------------------------------------------
// The Utility namespace is for functions
// which are useful but don't necessarily belong anywhere else.
 
namespace Utility
{
 
std::string system_info();
 
template <typename T>
class is_streamable
{
  template <typename U> // must be template to get SFINAE fall-through...
  static auto test(const U* u) -> decltype(std::cout << *u);
 
  static auto test(...) -> std::false_type;
 
public:
  enum { value = !std::is_same<decltype(test((T*)0)), std::false_type>::value };
};
 
#if defined(__GNUC__) && !defined(__INTEL_COMPILER) && !defined(__clang__)
#if (__GNUC__ > 12)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdangling-reference"
#endif
#endif
 
template<typename Map, typename Key,
         typename std::enable_if<!is_streamable<Key>::value, Key>::type* = nullptr>
inline
typename Map::mapped_type &
map_find(Map & map,
         const Key & key,
         const char * filename,
         int line_number)
{
  auto it = map.find(key);
  libmesh_error_msg_if(it == map.end(),
                       "map_find() error: key not found in file "
                       << filename << " on line " << line_number);
  return it->second;
}
 
template<typename Map, typename Key,
         typename std::enable_if<!is_streamable<Key>::value, Key>::type* = nullptr>
inline
const typename Map::mapped_type &
map_find(const Map & map,
         const Key & key,
         const char * filename,
         int line_number)
{
  auto it = map.find(key);
  libmesh_error_msg_if(it == map.end(),
                       "map_find() error: key not found in file "
                       << filename << " on line " << line_number);
  return it->second;
}
 
template<typename Map, typename Key,
         typename std::enable_if<is_streamable<Key>::value, Key>::type* = nullptr>
inline
typename Map::mapped_type &
map_find(Map & map,
         const Key & key,
         const char * filename,
         int line_number)
{
  auto it = map.find(key);
  libmesh_error_msg_if(it == map.end(),
                       "map_find() error: key \"" << key << "\" not found in file "
                       << filename << " on line " << line_number);
  return it->second;
}
 
template<typename Map, typename Key,
         typename std::enable_if<is_streamable<Key>::value, Key>::type* = nullptr>
inline
const typename Map::mapped_type &
map_find(const Map & map,
         const Key & key,
         const char * filename,
         int line_number)
{
  auto it = map.find(key);
  libmesh_error_msg_if(it == map.end(),
                       "map_find() error: key \"" << key << "\" not found in file "
                       << filename << " on line " << line_number);
  return it->second;
}
 
// The map_find functions are our only dangling-reference false positives
 
#if defined(__GNUC__) && !defined(__INTEL_COMPILER) && !defined(__clang__)
#if (__GNUC__ > 12)
#pragma GCC diagnostic pop
#endif
#endif
 
 
template<typename Vector>
inline
typename Vector::reference &
vector_at(Vector & vec,
          typename Vector::size_type i,
          const char * filename,
          int line_number)
{
  libmesh_error_msg_if(i >= vec.size(),
                       "vec_at() error: Index " << i <<
                       " past end of vector in file " << filename <<
                       " on line " << line_number);
  return vec[i];
}
 
template<typename Vector>
inline
typename Vector::const_reference &
vector_at(const Vector & vec,
          typename Vector::size_type i,
          const char * filename,
          int line_number)
{
  libmesh_error_msg_if(i >= vec.size(),
                       "vec_at() error: Index " << i <<
                       " past end of vector in file " << filename <<
                       " on line " << line_number);
  return vec[i];
}
 
 
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);
}
 
 
// When looking for a complicated suffix to a filename, we only want
// to consider the base name, without any preceding path name.
// "/tmp/foo.e25ad0/mesh.msh" is not ExodusII.
std::string_view basename_of(const std::string & fullname);
 
 
bool contains(std::string_view superstring,
              std::string_view substring);
 
 
bool ends_with(std::string_view superstring,
               std::string_view suffix);
 
 
// Utility functions useful when dealing with complex numbers.
 
#ifdef LIBMESH_USE_COMPLEX_NUMBERS
 
std::string complex_filename (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);
 
 
std::string unzip_file (std::string_view name);
 
 
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;
}
 
 
 
struct CompareUnderlying
{
  using is_transparent = void;
 
  template <class T>
  bool operator()(const std::unique_ptr<T> & a, const std::unique_ptr<T> & b) const
  {
    return a.get() < b.get();
  }
 
  template <class T>
  bool operator()(const std::unique_ptr<T> & a, const T * const & b) const
  {
    return a.get() < b;
  }
 
  template <class T>
  bool operator()(const T * const & a, const std::unique_ptr<T> & b) const
  {
    return a < b.get();
  }
};
 
} // namespace Utility
 
} // namespace libMesh
 
#endif // LIBMESH_UTILITY_H