Re: A missing (?) function: exponentfp(x)

[Ilya Zakharevich <nospam-abuse@ilyaz.org>]

On Wed, Sep 18, 2024 at 10:38:09AM +0200, Aurel Page wrote:
> ? install("exponentfp","G");
> ? exponentfp(2^30-1)
> %2 = 29.999999998656385002
> ? exponentfp(Pi)
> %3 = 1.6514961294723207175
> ? z = Pi*2^20
> %4 = 3294198.6583305710348142047482656880163
> ? for(i=1,10^6,exponent(z))
> cpu time = 276 ms, real time = 276 ms.
> ? for(i=1,10^6,exponentfp(z))
> cpu time = 312 ms, real time = 312 ms.

Hard to tell: on my (more than a decade old, cheap) laptop, the code
with exponent() takes 78 ms — but only 15 ms of them is taken by
exponent() itself.  Rescaling proportionally, this would make
exponentfp() twice as slow exponent() — which, if true, would be
REALLY GREAT!  Thanks!

However, to estimate THE REAL power of this, one needs to know the
timing of 

   ? for(i=1,10^6,(z))

(but I would redo everything with 10^8 — on some architectures
sub-0.1-seconds timing is not fully reliable…)5~

A Lot of Thanks again,
Ilya

  P.S.  Looking into the source, it probably does not support non-real
  	types; does it?

	For best results, it should better propagate better to other
  	types: fold()-by-max() for vectors/etc, fallback-to-exponent()
  	for non-real numeric types (etc?)…

	(All this is much easier to do from C — comparing to from gp…
	[Writing from experience!  Related: it is a pity that ## — for
	index-arity — is not yet implemented])