[Gcl-devel] Re: Mandelbrot for the terminal behaves differently with GCL and ABCL

[Peter Graves]

On Sun, 1 Aug 2004 at 13:12:03 +0200, Cristian Pietsch wrote:
> Incidentally, I have noticed that most implementations produce the
> same ``apple man'', but GCL, Armed Bear Common Lisp, Poplog, and
> LispWorks have their own version each. I don't know if this is caused
> by different precision arithmetic or different encodings.

One difference is that SBCL uses single floats by default, but ABCL
only supports double floats (this is permitted by the standard).

If you force SBCL to use double floats, the SBCL pattern looks more
like the ABCL pattern, but they are still a bit different.

If you print out z each time through the loop, you'll notice that in
some cases there are very small differences between the SBCL values
and the ABCL values. This is most likely caused by roundoff error in
one Lisp or the other; SBCL is probably closer to the truth.

-Peter