HP UX Fortran Software manual Increasing the precision of constants

stat_val = 1 auto_val = 124 stat_val = 2 auto_val = 1 stat_val = 3 auto_val = 65 stat_val = 4 auto_val = 65

NOTE: HP Fortran provides the AUTOMATIC and STATIC statements as porting extensions. The STATIC statement is functionally the same as the SAVE statement, and the AUTOMATIC statement may be used to declare a variable as automatic. However, such a declaration is generally pointless because variables compiled under HP Fortran are automatic by default.

The HP Fortran Programmer's Reference provides detailed information about the AUTOMATIC, SAVE, and STATIC statements.

Increasing the precision of constants

By default, HP Fortran evaluates all floating-point constants as single-precision. For example, the compiler treats following constant

3.14159265358979323846

as though you had specified:

3.1415927

Although the loss of precision might be acceptable when assigning to single-precision variables, it is might be less acceptable when assigning to double-precision variables or when using floating-point constants in expressions where the loss in precision might result in significant round-off differences.

NOTE: HP Fortran provides two ways to override the default precision of individual constants: the kind parameter and the exponent form. The kind parameter indicates the precision of floating-point constants: 4 for single-precision, 8 for double-precision, and 16 for quad-precision.

In the following example, the kind parameter _8 specifies that the constant is to be evaluated as double-precision:

3.14159265358979323846_8

To change the precision of all floating-point constants (except those having a kind parameter), you can use the +real_constantoption. This option takes two forms, +real_constant=double and +real_constant=single, which specify (respectively) double-precision and single-precision for floating-point constants in the files compiled with this option. The +real_constant=singleform is the default. Neither form of the option has any affect on constants that have the kind parameter.

To promote all floating-point constants in the source files x.f, y.f, and z.f, compile with the command line:

$ f90 +real_constant=double x.f y.f z.f

The +real_constant=singleoption specifies that all floating-point constants in a file are to be treated as single-precision (the default). The following command line specifies single-precision for all floating-point constants in the files a.f, b.f, andc.f :

$ f90 +real_constant=single a.f b.f c.f

Note that +real_constant=singledoes not demote constants that use either the kind parameter or the exponent form (for example, 4.0D0) .

For information about increasing the precision of variables, see “Increasing default data sizes” (page 70). The HP Fortran Programmer’s Reference describes the syntax of the kind parameter and the exponent form and the +real_constant option. For detailed information about how

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