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From: sjw <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing Ada with C
Date: Fri, 6 Aug 2010 01:39:18 -0700 (PDT)
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Date: 2010-08-06T01:39:18-07:00
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On Aug 5, 6:24=A0pm, Ada novice <po...@gmx.us> wrote:

> On Aug 5, 3:57=A0pm, sjw <simon.j.wri...@mac.com> wrote:
>
> > Although LAPACK/BLAS (at 3.2.2 anyway) allow you to build with
> > extended precision (80-bit floats, GNAT Long_Long_Float if on x86
> > hardware) GNAT's implementation of Generic * Arrays assumes the worst
> > case, ie BLAS/LAPACK only available in single & double precision; and
> > if the type in use (My_Float in my test case) doesn't match Fortran
> > single or double precision it converts to double precision, makes the
> > call, then converts back.
>
> Can we change the subtype to Long_Long_Float? This will be of 18
> precision digits and "more" precise than Fortran's double precision.
> It would be like asking for more precision that can be offered. Did I
> understand you correctly?

You can change to Long_Long_Float, and on an Intel machine that will
use 80 bits (on a PowerPC it won't; Long_Long_Float is the same as
Long_Float, because the FPU on a PPC doesn't support extended
precision (AFAIK)).

*BUT* *BUT* *BUT* the internals of the matrix operations (the standard
ones and our extensions) only use 64 bits. So the apparent extra
precision is fool's gold.