Tpetra_Details_shortSort.hpp

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#ifndef TPETRA_DETAILS_SHORTSORT_HPP
#define TPETRA_DETAILS_SHORTSORT_HPP


#include "TpetraCore_config.h"
#include "Kokkos_Macros.hpp"
#include <type_traits>

namespace Tpetra {
namespace Details {

// Make sure that the macro defined below wasn't defined somewhere else.
#ifdef TPETRA_DETAILS_SWAP_KEYSANDVALUES
#  error "The TPETRA_DETAILS_SWAP_KEYSANDVALUES macro is already defined."
#endif // TPETRA_DETAILS_SWAP_KEYSANDVALUES

#define TPETRA_DETAILS_SWAP_KEYSANDVALUES( i, j )  \
  if (keys[i] > keys[j]) { \
    const KeyType tmpKey (keys[i]); \
    keys[i] = keys[j]; \
    keys[j] = tmpKey; \
    const ValueType tmpVal (values[i]); \
    values[i] = values[j]; \
    values[j] = tmpVal; \
  }

// Make sure that the macro defined below wasn't defined somewhere else.
#ifdef TPETRA_DETAILS_SWAP_KEYS
#  error "The TPETRA_DETAILS_SWAP_KEYS macro is already defined."
#endif // TPETRA_DETAILS_SWAP_KEYSANDVALUES

#define TPETRA_DETAILS_SWAP_KEYS( i, j )  \
  if (keys[i] > keys[j]) { \
    const KeyType tmpKey (keys[i]); \
    keys[i] = keys[j]; \
    keys[j] = tmpKey; \
  }

template<class KeyType, class ValueType>
KOKKOS_FUNCTION void
shortSortKeysAndValues_2 (KeyType keys[2], ValueType values[2])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  For 2 entries, the sorting network is
  // nearly trivial.
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 1);
}

template<class KeyType>
KOKKOS_FUNCTION void
shortSortKeys_2 (KeyType keys[2])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  For 2 entries, the sorting network is
  // nearly trivial.
  TPETRA_DETAILS_SWAP_KEYS(0, 1);
}

template<class KeyType, class ValueType>
KOKKOS_FUNCTION void
shortSortKeysAndValues_3 (KeyType keys[3], ValueType values[3])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  To make the network, I used the generator
  // at
  //
  // http://pages.ripco.net/~jgamble/nw.html
  //
  // "Best" algorithm in this case is the Bose-Nelson Algorithm.
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 2);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 2);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 1);
}

template<class KeyType>
KOKKOS_FUNCTION void
shortSortKeys_3 (KeyType keys[3])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  To make the network, I used the generator
  // at
  //
  // http://pages.ripco.net/~jgamble/nw.html
  //
  // "Best" algorithm in this case is the Bose-Nelson Algorithm.
  TPETRA_DETAILS_SWAP_KEYS(1, 2);
  TPETRA_DETAILS_SWAP_KEYS(0, 2);
  TPETRA_DETAILS_SWAP_KEYS(0, 1);
}

template<class KeyType, class ValueType>
KOKKOS_FUNCTION void
shortSortKeysAndValues_4 (KeyType keys[4], ValueType values[4])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  To make the network, I used the generator
  // at
  //
  // http://pages.ripco.net/~jgamble/nw.html
  //
  // "Best" algorithm in this case is the Bose-Nelson Algorithm.
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 1);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(2, 3);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 2);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 3);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 2);
}

template<class KeyType>
KOKKOS_FUNCTION void
shortSortKeys_4 (KeyType keys[4])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  To make the network, I used the generator
  // at
  //
  // http://pages.ripco.net/~jgamble/nw.html
  //
  // "Best" algorithm in this case is the Bose-Nelson Algorithm.
  TPETRA_DETAILS_SWAP_KEYS(0, 1);
  TPETRA_DETAILS_SWAP_KEYS(2, 3);
  TPETRA_DETAILS_SWAP_KEYS(0, 2);
  TPETRA_DETAILS_SWAP_KEYS(1, 3);
  TPETRA_DETAILS_SWAP_KEYS(1, 2);
}

template<class KeyType, class ValueType>
KOKKOS_FUNCTION void
shortSortKeysAndValues_8 (KeyType keys[8], ValueType values[8])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  To make the network, I used the generator
  // at
  //
  // http://pages.ripco.net/~jgamble/nw.html
  //
  // "Best" algorithm in this case is the Bose-Nelson Algorithm.
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 1);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(2, 3);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 2);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 3);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 2);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(4, 5);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(6, 7);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(4, 6);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(5, 7);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(5, 6);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(0, 4);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 5);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(1, 4);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(2, 6);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(3, 7);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(3, 6);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(2, 4);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(3, 5);
  TPETRA_DETAILS_SWAP_KEYSANDVALUES(3, 4);
}

template<class KeyType>
KOKKOS_FUNCTION void
shortSortKeys_8 (KeyType keys[8])
{
  // Since this function takes a constant number of entries, I use a
  // sorting network here.  To make the network, I used the generator
  // at
  //
  // http://pages.ripco.net/~jgamble/nw.html
  //
  // "Best" algorithm in this case is the Bose-Nelson Algorithm.
  TPETRA_DETAILS_SWAP_KEYS(0, 1);
  TPETRA_DETAILS_SWAP_KEYS(2, 3);
  TPETRA_DETAILS_SWAP_KEYS(0, 2);
  TPETRA_DETAILS_SWAP_KEYS(1, 3);
  TPETRA_DETAILS_SWAP_KEYS(1, 2);
  TPETRA_DETAILS_SWAP_KEYS(4, 5);
  TPETRA_DETAILS_SWAP_KEYS(6, 7);
  TPETRA_DETAILS_SWAP_KEYS(4, 6);
  TPETRA_DETAILS_SWAP_KEYS(5, 7);
  TPETRA_DETAILS_SWAP_KEYS(5, 6);
  TPETRA_DETAILS_SWAP_KEYS(0, 4);
  TPETRA_DETAILS_SWAP_KEYS(1, 5);
  TPETRA_DETAILS_SWAP_KEYS(1, 4);
  TPETRA_DETAILS_SWAP_KEYS(2, 6);
  TPETRA_DETAILS_SWAP_KEYS(3, 7);
  TPETRA_DETAILS_SWAP_KEYS(3, 6);
  TPETRA_DETAILS_SWAP_KEYS(2, 4);
  TPETRA_DETAILS_SWAP_KEYS(3, 5);
  TPETRA_DETAILS_SWAP_KEYS(3, 4);
}

template<class KeyType, class ValueType, class IndexType>
KOKKOS_FUNCTION void
shellSortKeysAndValues (KeyType keys[],
                        ValueType values[],
                        const IndexType n)
{
  static_assert (std::is_integral<IndexType>::value,
                 "IndexType must be a signed integer type.");
  static_assert (std::is_signed<IndexType>::value,
                 "IndexType must be a signed integer type.  "
                 "This implementation does a count-down loop, "
                 "and may thus loop forever "
                 "if one attempts to use it with unsigned IndexType.");
  constexpr IndexType ZERO = 0;
  IndexType midpoint = n / static_cast<IndexType> (2);

  while (midpoint > ZERO) {
    // Avoid names like "max" in case they collide with macros.
    const IndexType theMax = n - midpoint;
    for (IndexType j = 0; j < theMax; ++j) {
      // IndexType is signed, so it's legit to compare >= 0.
      for (IndexType k = j; k >= 0; k -= midpoint) {
        if (keys[k + midpoint] >= keys[k]) {
          break;
        }
        const KeyType tmpKey = keys[k + midpoint];
        keys[k + midpoint] = keys[k];
        keys[k] = tmpKey;
        const ValueType tmpVal = values[k + midpoint];
        values[k + midpoint] = values[k];
        values[k] = tmpVal;
      }
    }
    midpoint = midpoint / 2;
  }
}

template<class KeyType, class IndexType>
KOKKOS_FUNCTION void
shellSortKeys (KeyType keys[], const IndexType n)
{
  static_assert (std::is_integral<IndexType>::value,
                 "IndexType must be a signed integer type.");
  static_assert (std::is_signed<IndexType>::value,
                 "IndexType must be a signed integer type.  "
                 "This implementation does a count-down loop, "
                 "and may thus loop forever "
                 "if one attempts to use it with unsigned IndexType.");
  constexpr IndexType ZERO = 0;
  IndexType midpoint = n / static_cast<IndexType> (2);

  while (midpoint > ZERO) {
    // Avoid names like "max" in case they collide with macros.
    const IndexType theMax = n - midpoint;
    for (int j = 0; j < theMax; ++j) {
      // IndexType must be signed, so it's legit to compare >= 0.
      for (int k = j; k >= 0; k -= midpoint) {
        if (keys[k + midpoint] >= keys[k]) {
          break;
        }
        const KeyType tmpKey = keys[k + midpoint];
        keys[k + midpoint] = keys[k];
        keys[k] = tmpKey;
      }
    }
    midpoint = midpoint / 2;
  }
}

} // namespace Details
} // namespace Tpetra

#endif // TPETRA_DETAILS_SHORTSORT_HPP