1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                       G N A T . H E A P _ S O R T                        --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--                     Copyright (C) 1995-2020, AdaCore                     --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  Sort utility (Using Heapsort Algorithm)
33
34--  This package provides a heapsort routine that works with access to
35--  subprogram parameters, so that it can be used with different types with
36--  shared sorting code.
37
38--  This heapsort algorithm uses approximately N*log(N) compares in the
39--  worst case and is in place with no additional storage required. See
40--  the body for exact details of the algorithm used.
41
42--  See also GNAT.Heap_Sort_G which is a generic version that will be faster
43--  since the overhead of the indirect calls is avoided, at the expense of
44--  generic code duplication and less convenient interface.
45
46--  Note: GNAT.Heap_Sort replaces and obsoletes GNAT.Heap_Sort_A, which is
47--  retained in the GNAT library for backwards compatibility.
48
49package GNAT.Heap_Sort is
50   pragma Pure;
51
52   --  The data to be sorted is assumed to be indexed by integer values
53   --  from 1 to N, where N is the number of items to be sorted.
54
55   type Xchg_Procedure is access procedure (Op1, Op2 : Natural);
56   --  A pointer to a procedure that exchanges the two data items whose
57   --  index values are Op1 and Op2.
58
59   type Lt_Function is access function (Op1, Op2 : Natural) return Boolean;
60   --  A pointer to a function that compares two items and returns True if
61   --  the item with index value Op1 is less than the item with Index value
62   --  Op2, and False if the Op1 item is greater than the Op2 item. If
63   --  the items are equal, then it does not matter if True or False is
64   --  returned (but it is slightly more efficient to return False).
65
66   procedure Sort (N : Natural; Xchg : Xchg_Procedure; Lt : Lt_Function);
67   --  This procedures sorts items in the range from 1 to N into ascending
68   --  order making calls to Lt to do required comparisons, and calls to
69   --  Xchg to exchange items. The sort is not stable, that is the order
70   --  of equal items in the input data set is not preserved.
71
72end GNAT.Heap_Sort;
73