g-heasor.ads   [plain text]

--                                                                          --
--                         GNAT RUNTIME COMPONENTS                          --
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--                       G N A T . H E A P _ S O R T                        --
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--  Sort utility (Using Heapsort Algorithm)

--  This package provides a heapsort routine that works with access to
--  subprogram parameters, so that it can be used with different types with
--  shared sorting code.

--  See also GNAT.Heap_Sort_G and GNAT.Heap_Sort_A. These are older versions
--  of this routine. In some cases GNAT.Heap_Sort_G may be a little faster
--  than GNAT.Heap_Sort, at the expense of generic code duplication and a
--  less convenient interface. The generic version also has the advantage
--  of being Pure, while this unit can only be Preelaborate.

--  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.

package GNAT.Heap_Sort is
pragma Preelaborate (Heap_Sort);

   --  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.

   type Xchg_Procedure is access procedure (Op1, Op2 : Natural);
   --  A pointer to a procedure that exchanges the two data items whose
   --  index values are Op1 and Op2.

   type Lt_Function is access function (Op1, Op2 : Natural) return Boolean;
   --  A pointer to a function that compares two items and returns True if
   --  the item with index value Op1 is less than the item with Index value
   --  Op2, and False if the Op1 item is greater than the Op2 item. If
   --  the items are equal, then it does not matter if True or False is
   --  returned (but it is slightly more efficient to return False).

   procedure Sort (N : Natural; Xchg : Xchg_Procedure; Lt : Lt_Function);
   --  This procedures sorts items in the range from 1 to N into ascending
   --  order making calls to Lt to do required comparisons, and calls to
   --  Xchg to exchange items. The sort is not stable, that is the order
   --  of equal items in the input data set is not preserved.

end GNAT.Heap_Sort;