Re: Target control of Fortran options

["N.M. Maclaren" <nmm1@cam.ac.uk>]

On Oct 4 2018, Paul Koning wrote:
>
> It appears that Fortran has a different approach. Fortran has syntax like 
> "REAL*8" to request a float of a specific size. And what gfortran does is 
> assume that "REAL" without a size specifier means "REAL*n" for a well 
> known fixed n. Without switches, n is 4, which is indeed the common 
> answer. But in my case, there isn't any 4-byte float type unless you say 
> -mfloat32.

If you don't have a 4-byte REAL, why do you make default REAL 4 bytes?
Do you mean that the front-end code assumes that it is?  In which case,
I would say that it's a clear design bug!  If not, why not just set it to
your basic floating type?

It's commonly 8 bytes on machines where that is the basic real size (e.g.
Cray vector systems); I don't know if gfortran supports any such systems,
but that's the approach that is universally taken for them.  In fact,
mapping REAL*4 to 8 bytes is quite common with precision-extension options
in some compilers, and your implementation sounds similar. 

I assume that you know that REAL*n isn't a standard Fortran facility, and
the "n" isn't always the size in bytes.  For the standard equivalent,
what does your version map REAL(SELECTED_REAL_SIZE(6)) to?


Regards,
Nick Maclaren.