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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                     G N A T . H E A P _ S O R T _ G                      --

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--                                 S p e c                                  --

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--                     Copyright (C) 1995-2006, AdaCore                     --

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-- GNAT is free software;  you can  redistribute it  and/or modify it under --

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-- Boston, MA 02110-1301, USA.                                              --

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-- As a special exception,  if other files  instantiate  generics from this --

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-- covered by the  GNU Public License.                                      --

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-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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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 version that works with subprogram access

--  parameters, allowing code sharing. The generic version is slightly more

--  efficient but does not allow code sharing and has an interface that is

--  more awkward to use.

--  There is also GNAT.Heap_Sort_A, which is now considered obsolete, but

--  was an older version working with subprogram parameters. This version

--  is retained for backwards compatibility with old versions of GNAT.

--  This heapsort algorithm uses approximately N*log(N) compares in the

--  worst case and is in place with no additional storage required. See

--  the body for exact details of the algorithm used.

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 value From to the data

   --  item with index value To (the old value in To being lost). An index

   --  value of zero is used for moves from and to a single temporary location.

   --  For best efficiency, this routine should be marked as inlined.

   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 the Op2 item. If the two items are equal, then

   --  it does not matter whether True or False is returned (it is slightly

   --  more efficient to return False). For best efficiency, this routine

   --  should be marked as inlined.

   --  Note on use of temporary location

   --  There are two ways of providing for the index value zero to represent

   --  a temporary value. Either an extra location can be allocated at the

   --  start of the array, or alternatively the Move and Lt subprograms can

   --  test for the case of zero and treat it specially. In any case it is

   --  desirable to specify the two subprograms as inlined and the tests for

   --  zero will in this case be resolved at instantiation time.

package GNAT.Heap_Sort_G is

   pragma Pure;

   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;