[Haskell-cafe] fast integer base-2 log function?

Uwe Hollerbach uhollerbach at gmail.com
Fri Feb 15 12:55:21 EST 2008

Yes, I suspect you are right. I didn't look into that in much detail,
although I did try exchanging "(2 ^ 50000000)" with "(1 `shiftL` 50000000)";
but that didn't make any difference.


On Fri, Feb 15, 2008 at 9:21 AM, Ryan Ingram <ryani.spam at gmail.com> wrote:

> On Thu, Feb 14, 2008 at 8:23 PM, Uwe Hollerbach <uhollerbach at gmail.com>
> wrote:
> >  Stefan's routine is, as expected, much much faster still: I tested the
> >  first two routines on numbers with 5 million or so bits and they took
> >  ~20 seconds of CPU time, whereas I tested Stefan's routine with
> >  numbers with 50 million bits, and it took ~11 seconds of CPU time.
> This seems wrong to me; that routine should take a small constant
> amount of time.  I suspect you are measuring the time to construct the
> 50-million bit numbers as well.  If you constructed a single number
> and called this routine on it several times I am sure you would get
> far different results, with the first routines taking ~7-11s each and
> Stefan's GHC/GMP-magic taking almost nothing.
>  -- ryan
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