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diff --git a/src/vhdl/vhdl-nodes_utils.ads b/src/vhdl/vhdl-nodes_utils.ads
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+--  Chain handling.
+--  Copyright (C) 2002, 2003, 2004, 2005 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.
+with Vhdl.Nodes; use Vhdl.Nodes;
+with Vhdl.Nodes_Meta;
+
+package Vhdl.Nodes_Utils is
+   --  Chains are simply linked list of iirs.
+   --  Elements of the chain are ordered.
+   --  Each element of a chain have a Chain field, which points to the next
+   --  element.
+   --  All elements of a chain have the same parent.  This parent contains
+   --  a field which points to the first element of the chain.
+   --  Note: the parent is often the value of the Parent field, but sometimes
+   --    not.
+
+   --  Chains can be covered very simply:
+   --      El : Iir;
+   --   begin
+   --      El := Get_xxx_Chain (Parent);
+   --      while El /= Null_Iir loop
+   --         * Handle element EL of the chain.
+   --         El := Get_Chain (El);
+   --      end loop;
+
+   --  However, building a chain is a little bit more difficult if elements
+   --  have to be appended.  Indeed, there is no direct access to the last
+   --  element of a chain.
+   --  An efficient way to build a chain is to keep the last element of it.
+
+   --  Return the number of elements in a chain starting with FIRST.
+   --  Not very efficient since O(N).
+   function Get_Chain_Length (First : Iir) return Natural;
+
+   --  Append CHAIN to the chain FIELD of node N.  Not very efficient.
+   procedure Append_Chain
+     (N : Iir; Field : Vhdl.Nodes_Meta.Fields_Enum; Chain : Iir);
+
+   --  These two subprograms can be used to build a sub-chain.
+   --  FIRST and LAST designates respectively the first and last element of
+   --  the sub-chain.
+
+   --  Set FIRST and LAST to Null_Iir.
+   procedure Sub_Chain_Init (First, Last : out Iir);
+   pragma Inline (Sub_Chain_Init);
+
+   --  Append element EL to the sub-chain.
+   procedure Sub_Chain_Append (First, Last : in out Iir; El : Iir);
+   pragma Inline (Sub_Chain_Append);
+
+   --  Append chain to the sub-chain.  FIRST_SUB and LAST_SUB must not be
+   --  Null_Iir.
+   procedure Sub_Chain_Append_Chain (First, Last : in out Iir;
+                                     First_Sub, Last_Sub : Iir);
+   procedure Sub_Chain_Append_Subchain (First, Last : in out Iir;
+                                        Sub : Iir);
+
+   --  Return TRUE iff CHAIN is of length one, ie CHAIN is not NULL_IIR
+   --  and chain (CHAIN) is NULL_IIR.
+   function Is_Chain_Length_One (Chain : Iir) return Boolean;
+   pragma Inline (Is_Chain_Length_One);
+
+   --  Insert EL after LAST.
+   procedure Insert (Last : Iir; El : Iir);
+
+   --  Insert EL after LAST and set LAST to EL.
+   procedure Insert_Incr (Last : in out Iir; El : Iir);
+end Vhdl.Nodes_Utils;