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------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME COMPONENTS --
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-- --
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-- G N A T . H E A P _ S O R T _ G --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1995-2005, AdaCore --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 2, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING. If not, write --
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-- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
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-- Boston, MA 02110-1301, USA. --
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-- --
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-- As a special exception, if other files instantiate generics from this --
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-- unit, or you link this unit with other files to produce an executable, --
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-- this unit does not by itself cause the resulting executable to be --
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-- covered by the GNU General Public License. This exception does not --
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-- however invalidate any other reasons why the executable file might be --
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-- covered by the GNU Public License. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- Heapsort generic package using formal procedures
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-- This package provides a generic heapsort routine that can be used with
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-- different types of data.
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-- See also GNAT.Heap_Sort, a version that works with subprogram access
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-- parameters, allowing code sharing. The generic version is slightly more
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-- efficient but does not allow code sharing and has an interface that is
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-- more awkward to use. The generic version is also Pure, while the access
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-- subprogram version can only be Preelaborate.
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-- There is also GNAT.Heap_Sort_A, which is now considered obsolete, but
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-- was an older version working with subprogram parameters. This version
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-- is retained for backwards compatibility with old versions of GNAT.
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-- This heapsort algorithm uses approximately N*log(N) compares in the
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-- worst case and is in place with no additional storage required. See
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-- the body for exact details of the algorithm used.
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generic
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-- The data to be sorted is assumed to be indexed by integer values from
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-- 1 to N, where N is the number of items to be sorted. In addition, the
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-- index value zero is used for a temporary location used during the sort.
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with procedure Move (From : Natural; To : Natural);
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-- A procedure that moves the data item with index value From to the data
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-- item with index value To (the old value in To being lost). An index
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-- value of zero is used for moves from and to a single temporary location.
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-- For best efficiency, this routine should be marked as inlined.
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with function Lt (Op1, Op2 : Natural) return Boolean;
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-- A function that compares two items and returns True if the item with
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-- index Op1 is less than the item with Index Op2, and False if the Op1
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-- item is greater than the Op2 item. If the two items are equal, then
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-- it does not matter whether True or False is returned (it is slightly
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-- more efficient to return False). For best efficiency, this routine
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-- should be marked as inlined.
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-- Note on use of temporary location
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-- There are two ways of providing for the index value zero to represent
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-- a temporary value. Either an extra location can be allocated at the
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-- start of the array, or alternatively the Move and Lt subprograms can
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-- test for the case of zero and treat it specially. In any case it is
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-- desirable to specify the two subprograms as inlined and the tests for
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-- zero will in this case be resolved at instantiation time.
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package GNAT.Heap_Sort_G is
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pragma Pure;
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procedure Sort (N : Natural);
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-- This procedures sorts items in the range from 1 to N into ascending
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-- order making calls to Lt to do required comparisons, and Move to move
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-- items around. Note that, as described above, both Move and Lt use a
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-- single temporary location with index value zero. This sort is not
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-- stable, i.e. the order of equal elements in the input is not preserved.
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end GNAT.Heap_Sort_G;
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