HP Fortran Programmer's Guide (B3908-90031; September 2011)

Controlling data storage
Increasing default data sizes
Chapter 3 109
Increasing default data sizes
The +autodbl and +autodbl4 options enable you to increase the default sizes (that is, the number of
storage bytes) for both constants and variables of default numeric and logical types. Unlike the
+real_constant option, the +autodbl and +autodbl4 options affect both constants and variables of
both real and integer types. (For information about using the +real_constant option, see “Increasing the
precision of constants” on page 107.)
When compiled with the +autodbl and +autodbl4 options, constants are treated as though they had
twice the default number of bytes (4) available for evaluating them. The effect of these options is to increase
the range of default integers and the precision of default reals.
The +autodbl and +autodbl4 options have no effect on the size of entities declared with the
CHARACTER, BYTE, or DOUBLE COMPLEX statements, nor on entities that are explicitly sized. That is, if a
variable is declared with a kind parameter or if a constant has a kind parameter, it is unchanged by
+autodbl or +autodbl4.
NOTE HP Fortran interprets the kind parameter as indicating the number of storage bytes to
allocate for a variable. When used with variables and constants of type real, the kind
parameter also indicates the precision: 4 for single-precision, 8 for double-precision, and
16 for quad-precision.
Promoting double-precision variables to quad-precision can have a severe impact on performance because
the instructions to perform quad-precision operations are implemented in software. If you are concerned
about performance and want to increase default data sizes, consider using the +autodbl4 option, which
does not promote variables declared with the DOUBLE PRECISION statement. There is no other difference
between +autodbl or +autodbl4.
These options affect all files on the command line. To increase the size or precision of selected variables and
constants, use the kind parameter.
Figure 3-1 on page 110 shows the default data types whose sizes are changed by the +autodbl and
+autodbl4 options.