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Date: Sun, 27 Sep 2009 23:27:52 +0200
From: Georg Bauhaus <rm.tsoh.plus-bug.bauhaus@maps.futureapps.de>
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Subject: Re: Tasking for Mandelbrot program
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Date: 2009-09-27T23:27:59+02:00
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Martin wrote:
> On Sep 27, 2:08 am, Georg Bauhaus <rm.tsoh.plus-
> bug.bauh...@maps.futureapps.de> wrote:
> [snip]
>>                   Z2 := (Z.re ** 2, Z.im ** 2);
> [snip]
> 
> Don't know about the rest of the program but on some platforms I've
> found it to be much faster to replace "** 2" with a straight
> multiplication, e.g. "Z.re * Z.re, Z.im * Z.im".

I have just checked.  The code that gcc is generating looks
the same for ** 2 and for * Z.xx.  Irrespective of either
sse instructions or i387 instructions.

Some more observations:

- SSE2 code performs 8% faster when suitable compilation options
  are present, -mfpmath=sse -msse2 (this is currently the case).
  Then digits 15 should probably stay in the declaration of Real.

- writing the image bytes with Stream_IO removes 6% running time
  when compared to GNAT.IO.Put.
  This adds standard Ada but also adds about 10 lines of code for
  the Put procedure and a Stdout variable. Is it worth it?