You can override this default with the +nosharedoption, which causes the linker to mark the executable as unshared, making the program’s code nonshareable. The following command line causes the linker to mark prog.f90as unshared:

$ f90 +noshared prog.f90

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 +DA2.0Woption (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 181 and Table on page 181 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.

Using environment variables

Environment variables are variables that are defined in the operating environment of the system and are available to various system components. For example, when you run a program, the shell looks at the PATHvariable to determine where the program is located. Table 2-15 lists and briefly describes the environment variables that control the way HP Fortran programs are compiled, linked, and run.

Table 24 HP Fortran environment variables

Environment variable

Description

 

 

F90ROOT

Specifies the alternate root for Fortran compiler and its

 

libraries.

 

 

ST_F90COM[64]

Specifies the path of 32-bit or 64-bit f90compiler

 

respectively in case of non-standard compiler path.

 

 

HP_F90OPTS

Specifies a list of command-line options that f90inserts in

 

the command line that invokes the HP Fortran compiler.

 

 

LPATH

Specifies a list of directories that the linker is to search for

 

libraries.

 

 

MP_NUMBER_OF_THREADS

Specifies the desired number of processors to be used to

 

run HP Fortran programs that have been compiled for

 

parallel execution.

 

 

Compiling in 64-bit mode 63