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

[Emanuel Berg]

Ihor Radchenko wrote:

>> 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.

A pretty good optimization! :O

But what kind of optimization is it?

Also, what happens if you remove the OPTIMIZE declaration
as well?

Still, isn't the rule of the "beat the benchmark" game to beat
it as fast as possible?

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