Adding UNION/MAP -- Feedback and tips pls!

[Thomas Koenig]

Am 04.03.2013 21:34, schrieb N.M. Maclaren:

(quoting documentation about DEC UNIONs for Fortran)

> "However, if you overlay one variable with another smaller variable,
> that portion of the initial variable is retained that is not overlaid.
> Depending on the application, the retained portion of an overlaid variable
> may or may not contain meaningful data and can be utilized at a later
> point in the program."

Ouch.

This seems to be at odds with C's unions, where it is not allowed to do
type punning.

This probably means that it would be necessary to present a DEC Fortran
union to the middle end as something like

union {
     char buff[8];
     double b;
     int c;
}

and then only do assignment with memcpy() to buff.

I think you're right - if we add this to gfortran, it should live behind

-fdo-you-really-want-to-use-dec-unions-yes-well-in-that-case-i-ll-let-you

or an options with a similar name.

	Thomas