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Date: Tue, 13 Oct 2009 14:57:06 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: Tasking for Mandelbrot program
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Date: 2009-10-13T14:57:07+02:00
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Gautier write-only schrieb:
> On 13 Okt., 11:11, Mark Lorenzen <mark.loren...@gmail.com> wrote:
> 
>> Please note that the "bit-wise or" operation in the following line has
>> no effect:
>>      Byte_Acc := Shift_Left (Byte_Acc, 1) or 16#00#
>>
>> When shifting left, you are guaranteed that zeroes are shifted in.
> 
> Well "or 0" has no effect anyway (shift or not shift). If you wanted
> to filter something, you would write "and 16#FFFFFF00# :-)

I'm stating the obvious when saying that the compiler
knows that "or 16#00#" has no effect... ;-)  FWIW, the
simple symmetric if/else around the above line seems
to give the fastest program with this distinction,
at least when produced by the Shootout compiler;
with GNATs such as GPL GNAT we might be able to reduce source
size by using Boolean'Pos instead of if/else or even anonymous
conditional expressions as are proposed for Ada 1Y.

Compile  with -gnatX if using GNAT, to see timing differences,
if any:


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

procedure Bittest is

   Byte_Acc : Unsigned_8;
   Ntests : constant := 100;

   procedure Work (This_Way: Boolean) is
      pragma Inline (Work);
   begin
      for K in 1 .. Ntests loop
	 Byte_Acc := Shift_Left (Byte_Acc, 1)
                       or
                     Boolean'Pos(not This_Way);
      end loop;
   end work;

   procedure Work2 (This_Way: Boolean) is  -- original
      pragma Inline (Work2);
   begin
      for K in 1 .. Ntests loop
	 if This_Way then
	    Byte_Acc := Shift_Left (Byte_Acc, 1) or 16#00#;
	 else
	    Byte_Acc := Shift_Left (Byte_Acc, 1) or 16#01#;
	 end if;
      end loop;
   end Work2;

   procedure WorkX (This_Way: Boolean) is
      pragma Inline (WorkX);
   begin
      for K in 1 .. Ntests loop
	 Byte_Acc := Shift_Left (Byte_Acc, 1) or (if This_Way
						    then 16#00#
						    else 16#01#);
      end loop;
   end WorkX;

   Start, Finish: Time;
begin
   Byte_Acc := Boolean'Pos(Argument_Count > 1);

   Start := Clock;
   for K in 1 .. 5_000_000 loop
      Work (Argument(1) = "yes");
   end loop;
   Finish := Clock;
   Put_Line ("Work: Byte_Acc = " & Unsigned_8'Image (Byte_Acc) &
	       " in " & Duration'Image (Finish - Start) & " seconds");

   Byte_Acc := Boolean'Pos(Argument_Count > 1);

   Start := Clock;
   for K in 1 .. 5_000_000 loop
      Work2 (Argument(1) = "yes");
   end loop;
   Finish := Clock;
   Put_Line ("Work2: Byte_Acc = " & Unsigned_8'Image (Byte_Acc) &
	       " in " & Duration'Image (Finish - Start) & " seconds");

   Byte_Acc := Boolean'Pos(Argument_Count > 1);

   Start := Clock;
   for K in 1 .. 5_000_000 loop
      WorkX (Argument(1) = "yes");
   end loop;
   Finish := Clock;
   Put_Line ("WorkX: Byte_Acc = " & Unsigned_8'Image (Byte_Acc) &
	       " in " & Duration'Image (Finish - Start) & " seconds");

end Bittest;