HP UX Fortran Software manual Increasing default data sizes

floating-point arithmetic is implemented on HP 9000 computers and how floating-point behavior affects the programmer, see the HP-UXFloating-Point Guide.

Increasing default data sizes

The +autodbland +autodbl4options 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 +autodbland +autodbl4options affect both constants and variables of both real and integer types. (For information about using the +real_constantoption, see “Increasing the precision of constants” (page 69).)

When compiled with the +autodbland +autodbl4options, 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 rails.

The +autodbl and +autodbl4 options have no effect on the size of entities declared with the CHARACTER, BYTE, or DOUBLE COMPLEXstatements, 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 +autodbl4option, 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.

“Increasing default data sizes” (page 70) shows the default data types whose sizes are changed by the +autodbl and +autodbl4 options.

Increasing default data sizes

Figure 2 Increasing default data sizes

70 Controlling data storage