Hi Waldek,
Waldek Hebisch <[EMAIL PROTECTED]> writes:
> Stephen Wilson wrote:
> > Stephen Wilson <[EMAIL PROTECTED]> writes:
> > > Could I suggest the following to replace these two cases:
> > >
> > > (+ 1 |negative| (round (log n 10)))
> >
> >
> > This should _not_ be used to replace both cases, but only the first.
> > I believe the second case might be OK unless the `over estimation'
> > is not enough account for the width in the negative case.
> >
> > However, these messages are now adrift a bit premature, so perhaps
> > someone may know of a better solution?
> >
>
> I looked at this code and I belive that I have written a better
> version (commited to wh-sandbox). Some remarks:
>
> - Ansi says that for exact arguments results are either exact or
> single precision. I feel that single precision give us no
> help so I use double precision arguments (as type gcl does not
> distingiush between single and double, but it stil gave only
> single precision result).
> - for moderate lengths if numerical result is suspect I use
> extra verification.
> - for large arguments I use over-estimate.
I think a log10 function like the one you implemented would certainly
be useful. A few questions:
- Has the code been tested on various lisps? I see the following
under gcl-2.7.0 for example:
(|axiom_log_10| 10) ==> 0
- Would you be willing to submit a patch with pamphlet
documentation?
We could use your log10 function to optimize the base 10 case. I
would also like to look into using mpz_sizeinbase as a more general
solution. Currently, exact calculation becomes slow when there are
more than 100000 decimal digits -- this is a fairly practical range
for the pretty printing of expressions, so there is not urgent need to
optimize IMHO.
Take care,
Steve
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