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From: "Clifford J. Nelson" <cnelson9@gte.net>
Subject: Re: Ada95 speed
Date: 1999/05/18
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Date: 1999-05-18T00:00:00+00:00
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David Starner wrote:

> "Clifford J. Nelson" 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.
>
> Was the code identical? I've had two Mandelbrot generators on the same
> system, and one took hours and one took seconds to do the Mandelbrot.
> Since the later was carefully and extensively tuned (cf. Fractint), I
> get the impression that the comparision code may have been similarily
> tuned.

Maybe not, but I think it showed 256 colors not just 64 like mine.

>
>
> >           exit when (abs( Z)) > 2.0;
>
> This line is probably the problem. The C code probably never did a sqrt;
> most likely, the code looked like (z.i* z.i + z.r * z.r) > 4.0. Do the
> same thing in Ada, and you'll probably see a huge improvement.

Yes! By a factor of five. Thanks. Here is the program again. It should run on
any Ada system I guess.

with Ada.Numerics.Complex_Types;
with Calendar;
with Ada.Text_io;
use Ada.Numerics.Complex_Types;
use Calendar;
use Ada.Text_io;

procedure timetest is

Ch : String (1..2);
procedure Display(Mag : in Float) is
    It : Integer;
    X, Y : Float;
    C, Z : Complex;
    Num_Iters : constant := 64;
    Vertical_Maximum : constant Short_Integer := 700;
    Horizontal_Maximum : constant Short_Integer := 1200;
    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
   Put(Duration'Image(Seconds(Clock)));
   Y := StartY;
   for Y_Pos in 0..700  loop
      X := StartX;
      for X_Pos in 0..1200 loop
        Z := (X, Y); -- Complex value; standard Ada 95!
        C := Z;
        for I in 0..Num_Iters loop
          It := I;
          exit when (Z.Re * Z.Re + Z.Im * Z.Im) > 4.0;
          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;
    Put(Duration'Image(Seconds(Clock)));
  end Display;

begin -- Main body of program timetest
   Display(0.0025); -- draw the fractal!
  Get(Ch);
end timetest;