g77.info: REAL() and AIMAG() of Complex

`REAL()' and `AIMAG()' of Complex

   The GNU Fortran language disallows `REAL(EXPR)' and `AIMAG(EXPR)',
where EXPR is any `COMPLEX' type other than `COMPLEX(KIND=1)', except
when they are used in the following way:

     REAL(REAL(EXPR))
     REAL(AIMAG(EXPR))

The above forms explicitly specify that the desired effect is to
convert the real or imaginary part of EXPR, which might be some `REAL'
type other than `REAL(KIND=1)', to type `REAL(KIND=1)', and have that
serve as the value of the expression.

   The GNU Fortran language offers clearly named intrinsics to extract
the real and imaginary parts of a complex entity without any conversion:

     REALPART(EXPR)
     IMAGPART(EXPR)

   To express the above using typical extended FORTRAN 77, use the
following constructs (when EXPR is `COMPLEX(KIND=2)'):

     DBLE(EXPR)
     DIMAG(EXPR)

   The FORTRAN 77 language offers no way to explicitly specify the real
and imaginary parts of a complex expression of arbitrary type,
apparently as a result of requiring support for only one `COMPLEX' type
(`COMPLEX(KIND=1)').  The concepts of converting an expression to type
`REAL(KIND=1)' and of extracting the real part of a complex expression
were thus "smooshed" by FORTRAN 77 into a single intrinsic, since they
happened to have the exact same effect in that language (due to having
only one `COMPLEX' type).

   _Note:_ When `-ff90' is in effect, `g77' treats `REAL(EXPR)', where
EXPR is of type `COMPLEX', as `REALPART(EXPR)', whereas with
`-fugly-complex -fno-f90' in effect, it is treated as
`REAL(REALPART(EXPR))'.

   *Note Ugly Complex Part Extraction::, for more information.