HP Fortran Programmer's Guide (September 2007)

Compiling and linking

Special-purpose compilations

Chapter 2 93

In some circumstances, it may help to debug a program or to improve its runtime performance

by making it nonshareable. In general, however, it is not desirable because nonshareable

executables place greater demands on memory resources.

Compiling in 64-bit mode

Compiling HP Fortran programs with the +DA2.0W option (PA-RISC only; for Itanium, use

+DD64) causes f90 to produce 64-bit executable programs. You should consider compiling in

64-bit mode if your program does any of the following:

• Accesses a large shared memory (greater than 1.75 gigabytes) or large data spaces

(greater than 1 gigabyte or, if using EXEC_MAGIC, greater than 1.9 gigabytes)

• Uses large data elements—greater than 32-bit words

• Provides objects or libraries that might be used in a 64-bit application

There are no HP Fortran language differences between 32-bit and

64-bit programs. Recompiling should sufﬁce to convert a 32-bit Fortran program to run as a

64-bit program.

However, the C language has some differences in data type sizes. If your Fortran program

calls functions written in C and is compiled in 64-bit mode, the size differences may require

promoting the data items that are passed to or from the C functions. See Table on page 176

and Table on page 176 for the size differences between Fortran and C data types when

compiled in 64-bit mode.

NOTE If your program does not need to run in 64-bit mode, there is no beneﬁt to

compiling it in 64-bit mode. In fact, the executable program may run slower

than if compiled in 32-bit mode.