Re: [bug-gawk] GAWK 4.1 arbitrary precision integers and E notation

[Hermann Peifer]

Hi Arnold,

Thanks for your time and explanations with which I do agree.

The only statement I do not agree is this one:
>    # 10^30 is 1e31, no?

See below. Hermann

$ gawk 'BEGIN{ print 10^1, 1e1}'
10 10



On 2013-10-18 9:28, Aharon Robbins wrote:
> Hi.
>
> I finally took another (short, sort of) look at this.
>
> > Date: Tue, 06 Aug 2013 07:41:35 +0200
> > From: Hermann Peifer <address@hidden>
> > To: address@hidden
> > Subject: [bug-gawk] GAWK 4.1 arbitrary precision integers and E notation
> >
> > As Arnold requested, I am forwarding the below snippet from a c.l.a.
> > posting to the bug-gawk mailing list.
> >
> > Hermann
> >
> > -------- Original Message --------
> > Subject: Re: GAWK 4.1 Integer Division
> > Date: Mon, 5 Aug 2013 19:26:36 +0000 (UTC)
> > From: address@hidden (Aharon Robbins)
> > Organization: A noiseless patient Spider
> > Newsgroups: comp.lang.awk
> > References: <address@hidden>
> > <address@hidden>
> > <address@hidden>
> > <address@hidden>
> >
> > Hermann Peifer  <address@hidden> wrote:
> > > # 10^30 obviously "looks like an integer" and is handled accordingly
> > > $ gawk -M 'BEGIN{print 10^30}'
> > > 1000000000000000000000000000000
> >
> > The MPFR code deals with this and figures it out.
> >
> > > # But 1e+30 doesn't seem to look like an integer..
> > > $ gawk -M 'BEGIN{print 1e+30}'
> > > 1000000000000000019884624838656
> >
> > The exponential form is by definition floating point.  This conversion
> > might be a bug. Can you file a bug report so that I'll look into it?
>
> I think this is just something we have to live with.  10^30 is correctly
> handled by the MPFR code and treated as integer since it's done at runtime,
> with big integers.
>
> The 1e30 is evaluated at parse time.  Even with -M, the *default* precision
> is 53, which is the same as double precision floating point. First,
> in floating point:
>
>         # 10^30 is 1e31, no?
>         $ ./gawk 'BEGIN { print 10^30 }'
>         1000000000000000019884624838656
>         $ ./gawk 'BEGIN { print 1e31 }'
>         9999999999999999635896294965248
>
> Now with MPFR:
>
>         $ ./gawk -M 'BEGIN { print 1e31 }'
>         9999999999999999635896294965248
>
> But if we increase the precision:
>
>         $ ./gawk -M  -vPREC=80 'BEGIN { print 1e31 }'
>         10000000000000000000000000000000
>
> I don't think there's a lot more to do here.  If (one day) gawk
> ever supports real decimal arithmetic, then maybe this will
> be straightened out.  Until then, anyone using MPFR will need
> to remember that they should increase the precision if they
> want more exact results.
>
> Thanks,
>
> Arnold