topic Re: 128 bit floating point real in Operating System - OpenVMS

128 bit floating point real

Neil Roberts — Fri, 04 Nov 2005 05:32:40 GMT

Hi,

I've had a user come to me asking about whether Alpha has support for 128 bit floating point reals (H-floating on VAX).

Any help on this would be appreciated.

thanks

Neil

Re: 128 bit floating point real

Ian Miller. — Fri, 04 Nov 2005 06:00:46 GMT

According to the migration manual
http://h71000.www7.hp.com/doc/73final/documentation/pdf/OVMS_MIGR_APPL.pdf

H float is not supported. Consider using X float which is IEEE extended double precision and has a similar range. There are compiler qualifers (depending on the language used) to select this and conversion routines to convert to various formats.

VAX code translated to Alpha using DECmigration can use H Float.

Re: 128 bit floating point real

Kris Clippeleyr — Fri, 04 Nov 2005 06:01:58 GMT

Neil,
The FORTRAN compiler supports REAL*16.
On VAX processors, H_floating format is used to implement REAL*16. On Alpha processors, IEEE X_floating format is used to implement REAL*16.
Regards,
Kris (aka Qkcl)

Re: 128 bit floating point real

Joseph Huber_1 — Fri, 04 Nov 2005 06:05:17 GMT

I don't know off-hand what floating type it is (depending on compile /FLOAT switches ?), but this quick test shows:

create f128.for
program f128
* test if we have real*16
real*16 test
test=1.1234567899999999
print *, ' ',test
print *, ' ',test/test
end Exit
fortran f128.for
link f128
run f128
1.12345683574676513671875000000000
1.00000000000000000000000000000000

Re: 128 bit floating point real

Joseph Huber_1 — Fri, 04 Nov 2005 06:49:46 GMT

In addition on Alphas, the DOUBLE PRECISION (F90 REAL(KIND=16)) can be made by default 128 bit (X-floating), with the /DOUBLE_SIZE=128 Fortran compiler switch.

Re: 128 bit floating point real

Neil Roberts — Fri, 04 Nov 2005 07:01:37 GMT

Thanks for all the responses.

Unfortunately we're using ADA rather than Fortran, which doesn't have the X or H switches available. Does anyone have any thoughts on the ADA side?

Neil

Re: 128 bit floating point real

Kris Clippeleyr — Fri, 04 Nov 2005 07:44:30 GMT

Neil,
AFAIK, on Alpha, the FORTRAN, the HP C, the HP Pascal compilers support 128-bit floating points (IEEE X_float); the ADA compiler does not.
Regards,
Kris (aka Qkcl)

Re: 128 bit floating point real

Ian Miller. — Fri, 04 Nov 2005 10:09:03 GMT

The manual I referenced has info on ADA. Search it for 128.

Re: 128 bit floating point real

Neil Roberts — Fri, 04 Nov 2005 12:44:10 GMT

Thank you all for your assistance. Looks like a Fortran licence may be in the offing!!

Neil

Re: 128 bit floating point real

Neil Roberts — Fri, 04 Nov 2005 12:45:25 GMT

No solution for problem. Time to look at Fortran.