NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/comp/lang/fortran/5200

Text File | 1993-01-28 | 1.9 KB | 42 lines

Newsgroups: comp.lang.fortran
Path: sparky!uunet!charon.amdahl.com!amdahl!rtech!pacbell.com!ames!agate!dog.ee.lbl.gov!hellgate.utah.edu!lanl!cochiti.lanl.gov!jlg
From: [e-mail] (J. Giles)
Subject: Re: IAND,IOR... - Thank you
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Los Alamos National Laboratory
References:  <[e-mail]>
Date: Tue, 26 Jan 1993 19:08:31 GMT
Lines: 30

In article <[e-mail]>, [e-mail] (Martin Kroeker) writes:
|> Many thanks to all who responded to my query about coding non-standard
|> bit manipulation functions in fortran, especially to Eric Haug, who provided
|> the simple (ouch !) solution in C:
|> long btest (long *a, long *b)
|>            return(*a>>*b);

This is clearly an incorrect solution.  Suppose the first argument is
eight and the second is one, this version of btest returns four - which
is *not* the value of the bit addressed by the second argument in either
big- or little-endian bit numbering.  In little-endian, the following
operation would be correct:

  long btest (long *a, long *b)
             return(*a>>*b & 1);

|> After my plea for help I had finally found a clumsy solution in fortran, but
|> this one naturally beats it easily.

I've never run across a Fortran implementation which did not have
these as operations as either intrinsic functions or operators which
are inlined and which use the hardware instructions (if the hardware
has them) to perform these operations.  A glance at the document for
your particular Fortran implementation would probably have revealed a
non-clumsy Fortran solution.  Certainly it's less clumsy to use a
implementation defined extension to Fortran than to rely on C (the
interface to which is also implementation defined and not portable).

--
J. Giles