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+--  Generic algorithms
+--  Copyright (C) 2016 Tristan Gingold
+--
+--  GHDL is free software; you can redistribute it and/or modify it under
+--  the terms of the GNU General Public License as published by the Free
+--  Software Foundation; either version 2, or (at your option) any later
+--  version.
+--
+--  GHDL is distributed in the hope that it will be useful, but WITHOUT ANY
+--  WARRANTY; without even the implied warranty of MERCHANTABILITY or
+--  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+--  for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with GHDL; see the file COPYING.  If not, write to the Free
+--  Software Foundation, 59 Temple Place - Suite 330, Boston, MA
+--  02111-1307, USA.
+
+package body Grt.Algos is
+   procedure Heap_Sort (N : Natural) is
+      --  An heap is an almost complete binary tree whose each edge is less
+      --  than or equal as its decendent.
+
+      --  Bubble down element I of a partially ordered heap of length N in
+      --  array ARR.
+      procedure Bubble_Down (I, N : Natural)
+      is
+         Child : Natural;
+         Parent : Natural := I;
+      begin
+         loop
+            Child := 2 * Parent;
+            if Child < N and then Lt (Child, Child + 1) then
+               Child := Child + 1;
+            end if;
+            exit when Child > N;
+            exit when not Lt (Parent, Child);
+            Swap (Parent, Child);
+            Parent := Child;
+         end loop;
+      end Bubble_Down;
+
+   begin
+      --  Heapify
+      for I in reverse 1 .. N / 2 loop
+         Bubble_Down (I, N);
+      end loop;
+
+      --  Sort
+      for I in reverse 2 .. N loop
+         Swap (1, I);
+         Bubble_Down (1, I - 1);
+      end loop;
+   end Heap_Sort;
+end Grt.Algos;