Re: Ada95 speed

["Clifford J. Nelson" <cnelson9@gte.net>]

Tucker,

 It takes ten seconds to do the computations alone. And another eleven
seconds to plot the pixels for a total of 21 seconds.

    Cliff Nelson

Tucker Taft wrote:

> Clifford J. Nelson (cnelson9@gte.net) wrote:
>
> : Ten years ago a Mandelbrot set computation and display on a 1200x700
> : screen with eight bit color took six seconds in C on a MacIIfx.
>
> : The following computations (leaving out all the with statements that you
> : need for the Mac) take ten seconds on an iMac 266 MHertz Mac OS 8.5.1
> : with the CodeBuilder Ada95 GNU from Tenon. I think it should run ten
> : times faster.
>
> : Is Ada95 slow in order to be safe?
>
> There is nothing in this code that would require any
> constraint checks.  You could put a "pragma Suppress(all_checks);"
> at the top of your source file to verify this.
>
> : Is GNU Ada95 slower than most Adas?
>
> Not particularly.
>
> : Is the iMac slow? Mac OS 8.5.1 slow?  CodeBuilder?
>
> The iMac is certainly much master than the MacIIfx in general,
> at least for pure computation.
>
> Probably the time is dominated by the drawing of the pixels.
> The only mildly complicated numeric operation in the code below is
> the call on "abs" for a complex number.  That involves 2 multiplies
> and a square-root.
>
> It would be useful to see where the time is going.  Chances are that
> the generated code is running much faster, and the time is all spent
> in the graphics routines drawing pixels.
>
> : Why does it take so long?
>
> My bet is on the graphic output routines.  The code generated
> by the Ada compiler is probably taking an immeasurably small amount
> of time.  Try changing the program so that it only does the computation.
> Then add back in the graphics output.  Measure the difference in
> execution time...
>
> : Program follows--------
>
> : with Ada.Numerics.Complex_Types;
> : use Ada.Numerics.Complex_Types;
>
> : procedure Mandel is
>
> : -- Initialize procedure goes here for windRect.bottom and windRect.top
>
> : procedure Display(Mag : in Float) is
> :     It : Integer;
> :     X, Y : Float;
> :     C, Z : Complex;
> :     Num_Iters : constant := 64;
> :     Vertical_Maximum : constant Short_Integer := windRect.bottom;
> :     Horizontal_Maximum : constant Short_Integer := windRect.Right;
> :     Ver_Size : constant Float := Float(Vertical_Maximum + 1);
> :     Hor_Size : constant Float := Float(Horizontal_Maximum + 1);
> :     StartY : constant Float := -Mag * Ver_Size;
> :     StartX : constant Float := -Mag * Hor_Size;
> :     Step : constant Float :=  2.0 * Mag ;
>
> :   begin
> :    Y := StartY;
> :    for Y_Pos in windRect.top..windrect.bottom - 1 loop
> :       X := StartX;
> :       for X_Pos in windRect.left..windRect.right loop
> :         Z := (X, Y); -- Complex value; standard Ada 95!
> :         C := Z;
> :         for I in 0..Num_Iters loop
> :           It := I;
> :           exit when (abs( Z)) > 2.0;
> :           Z := Z * Z + C; -- Complex arithmetic
> :         end loop;
> :     -- draw pixel here in color depending on variable It.
> :     X := X + Step;
> :     end loop;
> :    Y := Y + Step;
> :    end loop;
> :   end Display;
>
> : begin -- Main body of program Mandel
> :   Initialize;
> :    Display(0.0025); -- draw the fractal!
> :   loop
> :     exit when Events.Button;
> :   end loop;
> : end Mandel;
>
> --
> -Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
> Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
> AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA