HP Fortran Programmer's Guide (March 2010)

Controlling data storage
Increasing default data sizes
Chapter 3114
Finally, the program is compiled with the +autodbl4 option. As shown in the output, x is
promoted, but z is not:
$ f90 +autodbl4 precision2.f90
$ a.out
Stored in x: 3.14159265358979310000
Stored in y: 3.14159265358979323846
Stored in z: 3.14159265358979310000
Though useful for increasing the range and precision of numerical data, the +autodbl and
+autodbl4 options are especially useful when porting; see “Large word size” on page 242. For
detailed information about these options, see the HP Fortran Programmer’s Reference. For
detailed information about how floating-point arithmetic is implemented on HP 9000
computers and how floating-point behavior affects the programmer, refer to the HP-UX
Floating-Point Guide.