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From: Waldek Hebisch <hebisch@math.uni.wroc.pl>
Newsgroups: comp.lang.ada
Subject: Re: getting same output as gfortran, long_float
Date: Fri, 1 May 2015 15:39:27 +0000 (UTC)
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Date: 2015-05-01T15:39:27+00:00
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Nasser M. Abbasi <nma@12000.org> wrote:
> 
> Thanks, this is very useful. I noticed small difference in output:
> side-by-side:
> 
> Ada:          0.00182898948331047096479195244627343392775491540..
> Mathematica*: 0.00182898948331047096479195244627343392775491540..
> gfortran:     0.00182898948331047112025871115292829927
> 
> at digit 18, gfortran result is different. But your Ada rational
> package gives same result as Mathematica. This tells me your
> result is the accurate one !

Your previous gfortran result was:

1.82898948331047096479195244627343369E-3

which agrees with others... 

> humm....I do not know why these are different. I would have expected
> gfortran to be accurate for at least 34 digits, not just 18. May be
> I am doing something wrong in gfortran. Here is the gfortran again
> for reference:
> 
> -------------------
> PROGRAM foo
> IMPLICIT NONE
> REAL(KIND = 16) :: x  !-- kind=16 tells it is double quad
> x = 12.0D0 * 0.0001D0/(1.0D0 * (1.0D0 - 0.1D0)**4 )
> PRINT *, x
> END PROGRAM

AFAICS you have 34 digit x, but 17 digit constants.  So
it seems that you assign 17 digit number to x, no
wonder there is no gain in accuracy.

-- 
                              Waldek Hebisch
hebisch@antispam.math.uni.wroc.pl