[Info-vax] Roadmap

[Phillip Helbig undress to reply]

In article <nxgT6CmNy+$X at eisner.encompasserve.org>,
koehler at eisner.nospam.decuserve.org (Bob Koehler) writes: 

>    IIRC, Alpha supported all the VAX floating point formats, plus the
>    IEEE, except that IEEE 128 bit wasn't actually implemented in
>    hardware.  Or at least not in EV4.

I believe that there were two 64-bit floating-point types on VAX, but 
only one was really supported on ALPHA.  The other could be read and 
written, but internally was converted to the other type and back.

>From HELP FORTRAN:

               OpenVMS  VAX  systems  support   D_floating   and
               G_floating    implementations   of   the   DOUBLE
               PRECISION (REAL(KIND=8))  data  type  in  memory.
               OpenVMS  Alpha  systems  can  store  REAL(KIND=8)
               floating-point  data  in  memory  in  D_floating,
               G_floating, or T_floating format.

               Because  the  Alpha  instruction  set  does   not
               support  D_floating computations, D_floating data
               is converted to G_floating format for  arithmetic
               computations   and   then   converted   back   to
               D_floating format.   For  programs  that  perform
               many  REAL(KIND=8) computations, using D_floating
               data  is  slower   than   using   G_floating   or
               T_floating  data and the results will differ from
               VAX D_floating computations and results.

               Unless a program uses unformatted data  files  in
               D_floating  format, do not use the /FLOAT=D_FLOAT
               option.  If range and accuracy constraints do not
               disallow  the  use of the other REAL(KIND=8) data
               types, consider converting  existing  unformatted
               files  that  contain  D_floating  data to another
               format,  such  as  G_floating,   T_floating,   or
               X_floating  to  optimize  performance.  (For more
               information, see your user manual.)