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--  Heapsort generic package using formal procedures

--  This package provides a generic heapsort routine that can be used with
--  different types of data. See also GNAT.Heap_Sort_A, a version that works
--  with subprogram parameters, allowing code sharing. The generic version
--  is slightly more efficient but does not allow code sharing. The generic
--  version is also Pure, while the access version can only be Preelaborate.

generic
   --  The data to be sorted is assumed to be indexed by integer values from
   --  1 to N, where N is the number of items to be sorted. In addition, the
   --  index value zero is used for a temporary location used during the sort.

   with procedure Move (From : Natural; To : Natural);
   --  A procedure that moves the data item with index From to the data item
   --  with Index To. An index value of zero is used for moves from and to a
   --  single temporary location used by the sort.

   with function Lt (Op1, Op2 : Natural) return Boolean;
   --  A function that compares two items and returns True if the item with
   --  index Op1 is less than the item with Index Op2, and False if the Op1
   --  item is greater than or equal to the Op2 item.

package GNAT.Heap_Sort_G is
pragma Pure (Heap_Sort_G);

   procedure Sort (N : Natural);
   --  This procedures sorts items in the range from 1 to N into ascending
   --  order making calls to Lt to do required comparisons, and Move to move
   --  items around. Note that, as described above, both Move and Lt use a
   --  single temporary location with index value zero. This sort is not
   --  stable, i.e. the order of equal elements in the input is not preserved.

end GNAT.Heap_Sort_G;