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(g77-295.info)Double Notation

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Double Notation
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   The GNU Fortran language supports two uses of the keyword `DOUBLE'
to specify a specific kind of type:

   * `DOUBLE PRECISION', equivalent to `REAL(KIND=2)'

   * `DOUBLE COMPLEX', equivalent to `COMPLEX(KIND=2)'

   Use one of the above forms where a type name is valid.

   While use of this notation is popular, it doesn't scale well in a
language or dialect rich in intrinsic types, as is the case for the GNU
Fortran language (especially planned future versions of it).

   After all, one rarely sees type names such as `DOUBLE INTEGER',
`QUADRUPLE REAL', or `QUARTER INTEGER'.  Instead, `INTEGER*8',
`REAL*16', and `INTEGER*1' often are substituted for these,
respectively, even though they do not always have the same meanings on
all systems.  (And, the fact that `DOUBLE REAL' does not exist as such
is an inconsistency.)

   Therefore, this document uses "double notation" only on occasion for
the benefit of those readers who are accustomed to it.