1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                     G N A T . H E A P _ S O R T _ G                      --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--                     Copyright (C) 1995-2018, 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--  Heapsort generic package using formal procedures
33
34--  This package provides a generic heapsort routine that can be used with
35--  different types of data.
36
37--  See also GNAT.Heap_Sort, a version that works with subprogram access
38--  parameters, allowing code sharing. The generic version is slightly more
39--  efficient but does not allow code sharing and has an interface that is
40--  more awkward to use.
41
42--  There is also GNAT.Heap_Sort_A, which is now considered obsolete, but
43--  was an older version working with subprogram parameters. This version
44--  is retained for backwards compatibility with old versions of GNAT.
45
46--  This heapsort algorithm uses approximately N*log(N) compares in the
47--  worst case and is in place with no additional storage required. See
48--  the body for exact details of the algorithm used.
49
50generic
51   --  The data to be sorted is assumed to be indexed by integer values from
52   --  1 to N, where N is the number of items to be sorted. In addition, the
53   --  index value zero is used for a temporary location used during the sort.
54
55   with procedure Move (From : Natural; To : Natural);
56   --  A procedure that moves the data item with index value From to the data
57   --  item with index value To (the old value in To being lost). An index
58   --  value of zero is used for moves from and to a single temporary location.
59   --  For best efficiency, this routine should be marked as inlined.
60
61   with function Lt (Op1, Op2 : Natural) return Boolean;
62   --  A function that compares two items and returns True if the item with
63   --  index Op1 is less than the item with Index Op2, and False if the Op1
64   --  item is greater than the Op2 item. If the two items are equal, then
65   --  it does not matter whether True or False is returned (it is slightly
66   --  more efficient to return False). For best efficiency, this routine
67   --  should be marked as inlined.
68
69   --  Note on use of temporary location
70
71   --  There are two ways of providing for the index value zero to represent
72   --  a temporary value. Either an extra location can be allocated at the
73   --  start of the array, or alternatively the Move and Lt subprograms can
74   --  test for the case of zero and treat it specially. In any case it is
75   --  desirable to specify the two subprograms as inlined and the tests for
76   --  zero will in this case be resolved at instantiation time.
77
78package GNAT.Heap_Sort_G is
79   pragma Pure;
80
81   procedure Sort (N : Natural);
82   --  This procedures sorts items in the range from 1 to N into ascending
83   --  order making calls to Lt to do required comparisons, and Move to move
84   --  items around. Note that, as described above, both Move and Lt use a
85   --  single temporary location with index value zero. This sort is not
86   --  stable, i.e. the order of equal elements in the input is not preserved.
87
88end GNAT.Heap_Sort_G;
89