JiscMail Logo
Email discussion lists for the UK Education and Research communities

Help for COMP-FORTRAN-90 Archives


COMP-FORTRAN-90 Archives

COMP-FORTRAN-90 Archives


COMP-FORTRAN-90@JISCMAIL.AC.UK


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

COMP-FORTRAN-90 Home

COMP-FORTRAN-90 Home

COMP-FORTRAN-90  1999

COMP-FORTRAN-90 1999

Options

Subscribe or Unsubscribe

Subscribe or Unsubscribe

Log In

Log In

Get Password

Get Password

Subject:

Re: Extended precisions

From:

"robin" <[log in to unmask]>

Reply-To:

robin

Date:

Fri, 19 Mar 99 01:29:21 PST

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (119 lines)

Pierre Hugonnet wrote:

> robin wrote:

> > > REAL(selected_real_kind ( precision (1.0) + 1)) is also
> > > identical if there is no intermediate precision between
> > > default REAL and DOUBLE PRECISION kinds.
> >
> > Do you see a vendor providing such a one?
>
> Up to now, clearly no.
>
> But you cannot say that it will never be the case: Intel
> architecture is based on 10bytes reals (I think).

Intel is 4 bytes. Fout byte reals.

Double precision is 8 bytes (15 digits).

Extended precision is 10 bytes.
The floating-point unit handles 10 bytes.

> One could imagine
> in the future compilers supporting 8bytes as REAL, 16bytes
> as DOUBLE PRECISION, and in between 10bytes because it's
> the native format. I don't know if it's realistic, but it could
> happen.

unlikely.

> > > > And DOUBLE PRECISION does not work with COMPLEX.
> > > > With COMPLEX, you need to use something like that
> > > > which we have already elucidated, in order to obtain a
> > > > precision grreater than single precision.
> > > >
> > > > > Requesting a given precision is specifying explicitly the precision
> > > > > you want (p=6, p=12, ...)
> > > >
> > > > which is what " selected_real_kind ( precision (1.0) + 1)" does.
> > >
> > > It definitly doesn't: if I need 12 digits,
> >
> > It definitely does in the context of your original post, which
> > is what we were discussing [quoted from above]:
> >
> > "> > > it requests a precision greater
> > > > > than default REAL, that's all, like DOUBLE PRECISION (and I prefer
> > > > > this latter, which is more readable than
> > > > > selected_real_kind ( precision (1.0)) + 1) ) etc"
> >
> > > I can't use default REAL, since it is only 6 digits on most
> > > 32bits machines.
> >
> > But you were saying that you use a 64-bit machine.
> > Default real there is 15 or so digits.
>
> I use both 32bits and 64bits machines, and I want portable code
> which efficiently run on both (and also on other possible
> machines). I don't write code for a given a priori machine.

But if you use a 64-bit machine, then you would use default real.

> > > selected_real_kind ( precision (1.0) + 1) is OK on 32bits
> > > machines, but will give a ~30 digits
> > > kind (128bits) on some 64bits machines (Cray). default REAL
> > > (15 digits) would have been prefered, since 128bits kinds
> > > are generally software emulated and require more storage.
> >
> > And here [above] you confirm it.
>
> I just point the behaviors on both machines
>
> > To address this problem, you merely have to use
> > SELECTED_REAL_KIND (15).
>
> Yes, and it has been showed that in that case
> you cannot define generic interfaces...

On the contrary, we showed you precisely how to do
a generic interface for this.

> Moreover, YOU claimed that libraries should be written
> using REAL and DOUBLE PRECISION (or equivalent)
>
> > > If my algorithm requires some variables with 24 digits precision,
> > > you can not say it's excessive precision!
> >
> > Of course I can say that.  It's excessive precision
> > because it's not available on most systems (about 99.9% of them).
> > Did you read what I wrote above? :
> > "> > It's excessive precision because not many machines
> > > > support 24 digits.  To be portable, about 15 digits is
> > > > the maximum that can be "guaranteed".  "
>
> Then quadruple precision should never be used ?

Who said that?  Nobody said that.

> > > If you have a little moment, please could you write
> > > for me a library containing the previously described example of "mysum",
> > > with a generic interface, which is portable (assuming 24 digits
> > > precision exists),
> >
> > [Isn't this an oxymoron?  24 digits does not exist in any way
> > as portable.]
> >
> > > and which does not use more
> > > memory and CPU than necessary. I'm almost sure that you can
> > > not meet all of these requirements, but let's see...
> >
> > Anyway, we   all   have gone to some length to show you how
> > this can be done.  We have produced examples of declarations.
> > Best regards
> |          Pierre Hugonnet



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Top of Message | Previous Page | Permalink

JiscMail Tools


RSS Feeds and Sharing


Advanced Options


Archives

December 2023
February 2023
November 2022
September 2022
February 2022
January 2022
June 2021
November 2020
September 2020
June 2020
May 2020
April 2020
December 2019
October 2019
September 2019
March 2019
February 2019
January 2019
November 2018
October 2018
September 2018
August 2018
July 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
December 2015
November 2015
October 2015
September 2015
August 2015
June 2015
April 2015
March 2015
January 2015
December 2014
November 2014
October 2014
August 2014
July 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
July 2013
June 2013
May 2013
April 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
August 2010
July 2010
June 2010
March 2010
February 2010
January 2010
December 2009
October 2009
August 2009
July 2009
June 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
January 2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997


JiscMail is a Jisc service.

View our service policies at https://www.jiscmail.ac.uk/policyandsecurity/ and Jisc's privacy policy at https://www.jisc.ac.uk/website/privacy-notice

For help and support help@jisc.ac.uk

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager