gcc/ada/libgnat/g-hesorg.ads

   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) 1995-2017, 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
  50 generic
  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
  78 package 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
  88 end GNAT.Heap_Sort_G;