Z042: Calling a Subroutine by its Address

Author(s): J.Zoll, R.Brun et al.	Library: KERNLIB
Submitter: J. Zoll	Submitted: 27.04.1988
Language: Fortran or C or Assembler	Revised: 20.02.1995

The purpose of this package is to provide a (limited) tool to connect what is called a user-routine with an arbitrary name to a CALL in a package, pre-existing on a library.

Because on most machines JUMPXn is implemented in Fortran or C, separate entries are needed for calling the user-routine with zero, one, two, ..., nine parameters.

Structure:

SUBROUTINE subprogram
User Entry Names: JUMPAD, JUMPST, JUMPXn, ( )
Internal Entry Names: JUMPYn ( ) (if not Assembler or C)

Usage:

Three steps are necessary:

1)

Get the transfer address IAD of the routine (for example TARGET) to be called:

    EXTERNAL TARGET
    IAD=JUMPAD(TARGET)

2)

Set the transfer address for the next transfer(s):

    CALL JUMPST(IAD)

3)

Execute a transfer, for a call with parameters:

        CALL JUMPX0
    or  CALL JUMPX1(P1)
        ...
    or  CALL JUMPX9(P1,P2,P3,P4,P5,P6,P7,P8,P9)

Restrictions:

Since on most machines JUMPXn is written in Fortran or C, the call to JUMPXn will be found in the trace-back of routine TARGET, and RETURN from TARGET will pass through JUMPXn. Hence, normally (i.e. unless recursion is handled by a particular machine), TARGET or any of its called routines may not again call JUMPXn.