FORTRAN Reference Manual

Compiler Directives
FORTRAN Reference Manual—528615-001
10-41
LARGECOMMON Compiler Directive
LARGECOMMON directive. Use LARGECOMMON directives, not Guardian
procedure calls, if your program needs extended data space.
•
Executing Programs Compiled With LARGECOMMON
Accessing variables in normal user data space is faster than accessing variables in
extended data space. As a result, a program without LARGECOMMON directives
executes faster than an otherwise equivalent program that includes
LARGECOMMON directives.
•
Common Block Memory Allocation
Normally, FORTRAN allocates space for common blocks in the lower half of user
data segment.
Use the LARGECOMMON directive to allocate common blocks in extended
memory; use the HIGHCOMMON directive to allocate common blocks in the upper
half of the user data segment.
Examples
The following directive tells FORTRAN to allocate extended memory for all common
blocks in the compilation except those you explicitly list in HIGHCOMMON directives:
?LARGECOMMON
The following directive tells FORTRAN to allocate extended memory for common block
xxx:
?LARGECOMMON xxx
FORTRAN allocates all other common blocks in the compilation in the user data
segment unless you include additional LARGECOMMON directives that specify names
of other common blocks. The following directives tell FORTRAN to allocate extended
memory for four common blocks—aaa, bbb, ccc, and ddd:
?LARGECOMMON (aaa, bbb, ccc)
?LARGECOMMON ddd