Re: [PATCH] Re: Bignum performance (was: Shrinking the C core)

[Ihor Radchenko <yantar92@posteo.net>]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Ok.  I used the code from https://dataswamp.org/~incal/cl/fib.cl/fib.cl.
> ...
> The declaration means we are lying to the compiler because Z gets bigger 
> than 53 bits eventually.  And all bets are off because of the OPTIMIZE 
> declaration.  The result is that everything is done in fixnums on 64-bit 
> machines.

That explains a lot :)

I now tried

(defun fib (reps num)
  (declare (optimize speed (safety 0) (debug 0)))
  (let ((z 0))
    ;; (declare (type (unsigned-byte 53) reps num z))
    (dotimes (r reps)
      (let*((p1 1)
            (p2 1))
        (dotimes (i (- num 2))
          (setf z (+ p1 p2)
                p2 p1
                p1 z))))
    z))

and got

$ SBCL_HOME=/usr/lib64/sbcl perf record sbcl --load /tmp/fib.cl

;;;  0.263333 s real time
;;;  0.263641 s run time

$ ~/Git/emacs/src/emacs -Q -batch -l /tmp/fib.eln
0.739 s

Still ~3x faster compared to Elisp, but not orders of magnitude.

-- 
Ihor Radchenko // yantar92,
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