Index: tools/smaz.adb
==================================================================
--- tools/smaz.adb
+++ tools/smaz.adb
@@ -69,10 +69,11 @@
 
    package Options is
       type Id is
         (Base_256,
          Output_Ada_Dict,
+         Check_Roundtrip,
          Dictionary_Input,
          Decode,
          Encode,
          Evaluate,
          Filter_Threshold,
@@ -118,10 +119,11 @@
       Score_Method : Methods.Enum := Methods.Encoded;
       Action : Actions.Enum := Actions.Nothing;
       Ada_Dictionary : Ada.Strings.Unbounded.Unbounded_String;
       Hash_Package : Ada.Strings.Unbounded.Unbounded_String;
       Dict_Source : Dict_Sources.Enum := Dict_Sources.S_Expression;
+      Check_Roundtrip : Boolean := False;
    end record;
 
    overriding procedure Option
      (Handler  : in out Callback;
       Id       : in Options.Id;
@@ -643,10 +645,34 @@
                   for S of Data_List loop
                      Sx_Output.Append_String (Decompress (Dict, To_SEA (S)));
                   end loop;
                   Sx_Output.Close_List;
                end if;
+
+               if Handler.Check_Roundtrip then
+                  for S of Data_List loop
+                     declare
+                        use type Ada.Streams.Stream_Element_Array;
+                        Input : constant Ada.Streams.Stream_Element_Array
+                          := To_SEA (S);
+                        Processed : constant String
+                          := Decompress (Dict, Input);
+                        Roundtrip : constant Ada.Streams.Stream_Element_Array
+                          := Compress (Dict, Processed);
+                     begin
+                        if Input /= Roundtrip then
+                           Sx_Output.Open_List;
+                           Sx_Output.Append_String
+                             ("decompress-roundtrip-failed");
+                           Sx_Output.Append_Atom (Input);
+                           Sx_Output.Append_String (Processed);
+                           Sx_Output.Append_Atom (Roundtrip);
+                           Sx_Output.Close_List;
+                        end if;
+                     end;
+                  end loop;
+               end if;
 
                if Handler.Stat_Output then
                   declare
                      procedure Print_Line (Original, Output : Natural);
 
@@ -684,10 +710,31 @@
                   for S of Data_List loop
                      Sx_Output.Append_Atom (Compress (Dict, S));
                   end loop;
                   Sx_Output.Close_List;
                end if;
+
+               if Handler.Check_Roundtrip then
+                  for S of Data_List loop
+                     declare
+                        Processed : constant Ada.Streams.Stream_Element_Array
+                          := Compress (Dict, S);
+                        Roundtrip : constant String
+                          := Decompress (Dict, Processed);
+                     begin
+                        if S /= Roundtrip then
+                           Sx_Output.Open_List;
+                           Sx_Output.Append_String
+                             ("compress-roundtrip-failed");
+                           Sx_Output.Append_String (S);
+                           Sx_Output.Append_Atom (Processed);
+                           Sx_Output.Append_String (Roundtrip);
+                           Sx_Output.Close_List;
+                        end if;
+                     end;
+                  end loop;
+               end if;
 
                if Handler.Stat_Output then
                   declare
                      procedure Print_Line (Original, Output, Base64 : Natural);
 
@@ -1095,10 +1142,13 @@
          when Options.Base_256 =>
             Handler.Algorithm := Algorithms.Base_256;
 
          when Options.Base_256_Retired =>
             Handler.Algorithm := Algorithms.Base_256_Retired;
+
+         when Options.Check_Roundtrip =>
+            Handler.Check_Roundtrip := True;
       end case;
    end Option;
 
 
    function Activate_Dictionary (Dict : in Natools.Smaz_256.Dictionary)
@@ -1174,10 +1224,11 @@
       use Options;
       R : Getopt.Configuration;
    begin
       R.Add_Option ("base-256",      '2', No_Argument,       Base_256);
       R.Add_Option ("ada-dict",      'A', Optional_Argument, Output_Ada_Dict);
+      R.Add_Option ("check",         'C', No_Argument,       Check_Roundtrip);
       R.Add_Option ("decode",        'd', No_Argument,       Decode);
       R.Add_Option ("dict",          'D', No_Argument,       Dictionary_Input);
       R.Add_Option ("encode",        'e', No_Argument,       Encode);
       R.Add_Option ("evaluate",      'E', No_Argument,       Evaluate);
       R.Add_Option ("filter",        'F', Required_Argument, Filter_Threshold);
@@ -1405,10 +1456,15 @@
 
             when Options.Base_256_Retired =>
                New_Line (Output);
                Put_Line (Output, Indent & Indent
                  & "Use retired base-256 implementation");
+
+            when Options.Check_Roundtrip =>
+               New_Line (Output);
+               Put_Line (Output, Indent & Indent
+                 & "Check roundtrip of compression or decompression");
          end case;
       end loop;
    end Print_Help;
 
 
@@ -1432,11 +1488,12 @@
 
    if not Handler.Need_Dictionary then
       return;
    end if;
 
-   if not (Handler.Stat_Output or Handler.Sx_Output) then
+   if not (Handler.Stat_Output or Handler.Sx_Output or Handler.Check_Roundtrip)
+   then
       Handler.Sx_Output := True;
    end if;
 
    Read_Input_List :
    declare