Re: Performance of the Streams 'Read and 'Write

[Gautier write-only <gautier_niouzes@hotmail.com>]

Here is a test program. I am curious about other results

-- Usage: test_stream_performance <file>
-- Produces two .tmp files that are copies of <file>.
--
-- Example of output with file m.wmv, 2.59 MB, GNAT GPL 2008 / Win32:
--
--  xxx'Write / xxx'Read (Attribute).. 1.925210886 seconds
--  Workaround with SE buffer......... 0.049318559 seconds
--  Factor 39.036235547

--  Buffer size in bits..... 8192
--  SE Buffer size in bits.. 8192

with Ada.Calendar;                      use Ada.Calendar;
with Ada.Text_IO;
with Ada.Streams.Stream_IO;             use Ada.Streams.Stream_IO;
with Ada.Command_Line;                  use Ada.Command_Line;
with Interfaces;                        use Interfaces;

procedure Test_Stream_Performance is

  f_in, f_out: Ada.Streams.Stream_IO.File_Type;

  buffer_size, SE_buffer_size: Natural:= 0;
  -- To check if buffers could be overlapped (packing)

  type Buffer is array(Natural range <>) of Unsigned_8;

  ------------------------------------------------
  -- 1) Stream attributes - xxx'Read, xxx'Write --
  ------------------------------------------------

  -- Usually we would just have: Buffer'Read(Stream(f_in), b);
  -- Here we care about end of file.

  procedure Read_Attribute( b: out Buffer; last_read: out Natural ) is
    idx: constant Positive_Count:= Index(f_in);
    siz: constant Positive_Count:= Size(f_in);
  begin
    if End_Of_File(f_in) then
      last_read:= b'First-1;
    else
      last_read:= Natural'Min(b'First+Natural(siz-idx),b'Last);
      Buffer'Read(Stream(f_in), b(b'First .. last_read));
    end if;
  end Read_Attribute;

  procedure Write_Attribute( b: in Buffer ) is
  begin
    if buffer_size = 0 then
      buffer_size:= b'size;
    end if;
    Buffer'Write(Stream(f_out), b);
  end Write_Attribute;

  --------------------------------------------
  -- 2) The Stream_Element_Array workaround --
  --------------------------------------------

  procedure Read_SE( b: out Buffer; last_read: out Natural ) is
    use Ada.Streams;
    First     : constant Stream_Element_Offset:= Stream_Element_Offset
(b'First);
    Last      :          Stream_Element_Offset:= Stream_Element_Offset
(b'Last);
    SE_Buffer : Stream_Element_Array (First..Last);
  begin
    Read(Stream(f_in).all, SE_Buffer, Last);
    for i in First..Last loop
      b(Natural(i)):= Unsigned_8(SE_Buffer(i));
    end loop;
    last_read:= Natural(last);
  end Read_SE;

  procedure Write_SE( b: in Buffer ) is
    use Ada.Streams;
    First     : constant Stream_Element_Offset:= Stream_Element_Offset
(b'First);
    Last      : constant Stream_Element_Offset:= Stream_Element_Offset
(b'Last);
    SE_Buffer : Stream_Element_Array (First..Last);
  begin
    if SE_buffer_size = 0 then
      SE_buffer_size:= SE_Buffer'size;
    end if;
    for i in SE_Buffer'Range loop
      SE_Buffer(i):= Stream_Element(b(Natural(i)));
    end loop;
    Write(Stream(f_out).all, SE_Buffer);
  end Write_SE;

  name : constant String:= Argument(1);

  generic
    label: String;
    with procedure Read( b: out Buffer; last_read: out Natural  );
    with procedure Write( b: in Buffer  );
  procedure Test;

  procedure Test is
    b: Buffer(1..1024);
    l: Natural;
  begin
    Open(f_in, In_File, name);
    Create(f_out, Out_File, name & "_$$$_" & label & ".tmp");
    while not End_of_File(f_in) loop
      Read(b,l);
      Write(b(1..l));
    end loop;
    Close(f_out);
    Close(f_in);
  end;

  procedure Test_Attribute is new Test("Attribute", Read_Attribute,
Write_Attribute);
  procedure Test_SE is new Test("SE", Read_SE, Write_SE);

  T0, T1, T2: Time;

  use Ada.Text_IO;

begin
  T0:= Clock;
  Test_Attribute;
  T1:= Clock;
  Test_SE;
  T2:= Clock;
  Put_Line("xxx'Write / xxx'Read (Attribute).." & Duration'Image(T1-
T0) & " seconds");
  Put_Line("Workaround with SE buffer........." & Duration'Image(T2-
T1) & " seconds");
  Put_Line("Factor" & Duration'Image((T1-T0)/(T2-T1)));
  New_Line;
  Put_Line("Buffer size in bits....." & Integer'Image(buffer_size));
  Put_Line("SE Buffer size in bits.." & Integer'Image
(SE_buffer_size));
end;