CA Compress/2 › Linking Subroutines With Applications

Linking Subroutines With Applications

The Super Express subroutines, SHRINKZ and EXPANDZ; the Standard Tables subroutines, SHRINKS and EXPANDS; and the Hardware Compression subroutines, SHRKHCS and SHRKHCX, can be included explicitly via the linkage editor INCLUDE statement or resolved implicitly from SYSLIB.

CA Compress/2 provides two methods to link edit the SHRINK, EXPAND and CLOSE subroutines with application programs. In the first method, SHRINK, EXPAND, and CLOSE are link edited with the user's application program by including the module SHRKEXPD using an explicit INCLUDE linkage editor control statement. This method results in making a copy of the subroutines a part of the application program load module.

The second method provides an improved capability for link editing the SHRINK, EXPAND and CLOSE subroutines with the user's application program. The subroutines are link edited by including the module SHRKSTUB via an explicit INCLUDE linkage editor control statement. This module contains entry points for SHRINK, EXPAND and CLOSE and functions as a loader. Because SHRKSTUB does not support the Super Express entry points, SHRINKZ and EXPANDZ; the Standard Tables entry points, SHRINKS and EXPANDS; or the Hardware Compression entry points, SHRKHCS and SHRKHCX, this method is not available for Super Express, Standard Tables, or Hardware Compression.

The first CALL to a particular subroutine causes SHRKSTUB to load the correct subroutine from the CA Compress/2 library. Subsequent calls to that subroutine result in a direct branch to the previously loaded subroutine with several important advantages:

• Because copies of CA Compress/2 modules are not link edited into multiple application programs, library space is conserved.
• Application programs do not have to be relink edited when a new release of CA Compress/2 is installed. The subroutine support can reside on a single shared library.
• Application programs link edited with the SHRKEXPD module must be relinked each time a CA Compress subroutine is changed. Programs link edited with the SHRKSTUB module require no modification when a subroutine is changed because the fixed module is loaded from the CA Compress/2 library at execution.
• The subroutines can be shared between tasks. Attached modules are link edited only with the SHRKSTUB module (approximately 200 bytes).

To use this method, the CA Compress/2 library must either be in the linklist or supplied through STEPLIB or JOBLIB.