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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

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

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                     Copyright (C) 1995-2008, AdaCore                     --

--                                                                          --

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

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

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

--                                                                          --

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

-- unit, or you link  this unit with other files  to produce an executable, --

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-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- 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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--  Sort utility (Using Heapsort Algorithm)

--  This package provides a heapsort routine that works with access to

--  subprogram parameters, so that it can be used with different types with

--  shared sorting code.

--  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.

--  See also GNAT.Heap_Sort_G which is a generic version that will be faster

--  since the overhead of the indirect calls is avoided, at the expense of

--  generic code duplication and less convenient interface.

--  Note: GNAT.Heap_Sort replaces and obsoletes GNAT.Heap_Sort_A, which is

--  retained in the GNAT library for backwards compatibility.

package GNAT.Heap_Sort is

   pragma Pure;

   --  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.

   type Xchg_Procedure is access procedure (Op1, Op2 : Natural);

   --  A pointer to a procedure that exchanges the two data items whose

   --  index values are Op1 and Op2.

   type Lt_Function is access function (Op1, Op2 : Natural) return Boolean;

   --  A pointer to a function that compares two items and returns True if

   --  the item with index value Op1 is less than the item with Index value

   --  Op2, and False if the Op1 item is greater than the Op2 item. If

   --  the items are equal, then it does not matter if True or False is

   --  returned (but it is slightly more efficient to return False).

   procedure Sort (N : Natural; Xchg : Xchg_Procedure; Lt : Lt_Function);

   --  This procedures sorts items in the range from 1 to N into ascending

   --  order making calls to Lt to do required comparisons, and calls to

   --  Xchg to exchange items. The sort is not stable, that is the order

   --  of equal items in the input data set is not preserved.

end GNAT.Heap_Sort;