[racket] ~r: formatting 0.0 with 'exponential and #:precision

Correct, my message has nothing to do with the initial problem.
Jos 

> -----Original Message-----
> From: Dmitry Pavlov [mailto:dpavlov at ipa.nw.ru] 
> Sent: miércoles, 08 de mayo de 2013 12:11
> To: Jos Koot
> Cc: users at racket-lang.org
> Subject: Re: [racket] ~r: formatting 0.0 with 'exponential 
> and #:precision
> 
> Hi Jos,
> 
> I have nothing sensible to say about line 340 and
> the fix you propose (probably it is right), but the
> initial problem with 0.0 originates not in line 340
> but rather in lines 330-331
> 
> (if (zero? N-abs)
>      (values 0 0 (if exactly? significand-precision 0))
> 
> or line 311
> 
> [exponent (- significand-precision e-adjust)
> 
> When we do (~r 0.0 #:notation 'exponential #:precision 4),
> significand-precision is equal to 4 and e-adjust happens
> to be zero.
> 
> 
> Regards,
> 
> Dmitry
> 
> 
> 
> On 05/08/2013 11:21 AM, Jos Koot wrote:
> > I came across another thing:
> >
> > #lang racket
> >
> > (define x #e100.e-50000)
> > (rational? x) ; #t
> > (log x) ; -inf.0
> > (exact->inexact x); 0.0
> > (~r x #:notation 'exponential) ; error inexact->exact: no exact
> > representation
> >    number: -inf.0
> >
> > I think this is introduced in line 340 of racket/format.rkt 
> which contains:
> > (inexact->exact (floor (/ (log N-abs) (log base))))
> > for the first estimate of the order of magnitude.
> >
> > As the docs of ~r say "The exactness or inexactness of x 
> does not affect its
> > formatting.", this behaviour may well be intentional.
> >
> > It is possible though to avoid the error by subtracting the 
> log of the
> > denominator from that of the nominator after conversion to 
> exact rational.
> > Proc order-of-magnitude (in math I think) does this, but is 
> for base 10
> > only. May be I should adapt order-of-magnitude such as to 
> accept a base
> > argument?
> >
> > Best wishes, Jos
> >
> >> -----Original Message-----
> >> From: users-bounces at racket-lang.org
> >> [mailto:users-bounces at racket-lang.org] On Behalf Of Dmitry Pavlov
> >> Sent: martes, 07 de mayo de 2013 19:12
> >> To: users at racket-lang.org
> >> Subject: [racket] ~r: formatting 0.0 with 'exponential and 
> #:precision
> >>
> >> Hello,
> >>
> >> I just came across the following oddness with formatting
> >> of real numbers:
> >>
> >>   > (~r 1.0 #:notation 'exponential #:precision '(= 4))
> >> "1.0000e+00"
> >>
> >> OK
> >>
> >>
> >>   > (~r 0.0 #:notation 'exponential #:precision '(= 4))
> >> "0.e+04"
> >>
> >> ???
> >>
> >> Is there a rational explanation of why did
> >> the requested precision go into the exponent
> >> number for 0.0?
> >>
> >> Thanks.
> >>
> >>
> >> Best regards,
> >>
> >> Dmitry
> >> ____________________
> >>    Racket Users list:
> >>    http://lists.racket-lang.org/users
> >
> >
> >
>