Index: src/natools-s_expressions-atom_buffers.adb
==================================================================
--- src/natools-s_expressions-atom_buffers.adb
+++ src/natools-s_expressions-atom_buffers.adb
@@ -88,10 +88,33 @@
    begin
       Preallocate (Buffer, Data'Length);
       Buffer.Ref.Update (Process'Access);
    end Append_Reverse;
 
+
+   procedure Invert (Buffer : in out Atom_Buffer) is
+      procedure Process (Data : in out Atom);
+
+      procedure Process (Data : in out Atom) is
+         Low : Count := Data'First;
+         High : Count := Buffer.Used;
+         Tmp : Octet;
+      begin
+         while Low < High loop
+            Tmp := Data (Low);
+            Data (Low) := Data (High);
+            Data (High) := Tmp;
+            Low := Low + 1;
+            High := High - 1;
+         end loop;
+      end Process;
+   begin
+      if not Buffer.Ref.Is_Empty then
+         Buffer.Ref.Update (Process'Access);
+      end if;
+   end Invert;
+
 
    function Length (Buffer : Atom_Buffer) return Count is
    begin
       return Buffer.Used;
    end Length;

Index: src/natools-s_expressions-atom_buffers.ads
==================================================================
--- src/natools-s_expressions-atom_buffers.ads
+++ src/natools-s_expressions-atom_buffers.ads
@@ -44,10 +44,13 @@
       --  Append Data after the end of Buffer
 
    procedure Append_Reverse (Buffer : in out Atom_Buffer; Data : in Atom);
       --  Append bytes from Atom from last to first
 
+   procedure Invert (Buffer : in out Atom_Buffer);
+      --  Invert the order of bytes (first becomes last, etc)
+
    function Length (Buffer : Atom_Buffer) return Count;
    function Data (Buffer : Atom_Buffer) return Atom;
    procedure Query
      (Buffer : in Atom_Buffer;
       Process : not null access procedure (Data : in Atom));