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-- --
-- --
-- G N A T . H E A P _ S O R T _ G --
-- --
-- S p e c --
-- --
-- Copyright (C) 1995-2021, 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 3, 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 --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
-- 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.
-- 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;