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From: bernhold@red8 (David E. Bernholdt)
Newsgroups: comp.lang.fortran
Subject: Re: DEC System 5000 f77 bug
Message-ID: <28913@uflorida.cis.ufl.EDU>
Date: 3 Jun 91 16:45:42 GMT
References: <1694@usage.csd.unsw.oz.au> <3627@charon.cwi.nl>
Sender: news@uflorida.cis.ufl.EDU
Organization: Quantum Theory Project, Univ. of Florida
Lines: 49

In article <3627@charon.cwi.nl> dik@cwi.nl (Dik T. Winter) writes:
>Of course, this does not help if you get code you will run; but than the
>problem remains with other library (non-instrinsic) routines (eg, BLAS SAXPY
>etc.).  Some change of source is required anyhow.

If you have access to (and are willing to use) a macro preprocessor of
some sort, it can be quite helpful in simplifying precision changes
for routines such as the BLAS, LAPACK, etc. with precision-dependent
routine names.

For example, I use C-preprocessor on unix systems.  I have include
files blas.h, linpack.h, etc.  which are included at the beginning of
any Fortran routine which uses a given library.  The include files
contain a macro definition for each double or double complex routine
in the library mapping it onto the real/complex counterpart.  The
macro definitions are made only if an appropriate symbol is defined,
so the macro definitions are used or not based on a single symbol
definition.

Then you code everything in one precision, and if you need the other,
you run the preprocessor over it with the appropriate symbol
definition.

If you want to limit yourself to using only "include" preprocessing,
you can get the same effect at the expense of a little extra
discipline in coding.  Instead of something like

      Call DAXPY(N, A, X, IX, Y, IY)

you write

      include 'daxpy'
     $   (N, A, X, IX, Y, IY)

with the include file containing the "Call DAXPY".  Then to change
precision, you substitute a set of files with the other precision
routines.

It's just an automated way of handling the source code changes,
really, but I've found it quite useful.

P.S.  If anyone wants my CPP definitions for BLAS and LINPACK, I can
save you the trouble of typing them all in.

-- 
David Bernholdt			bernhold@qtp.ufl.edu
Quantum Theory Project		bernhold@ufpine.bitnet
University of Florida
Gainesville, FL  32611		904/392 6365