#: 17755 S12/OS9/68000 (OSK)
    18-Mar-93  16:27:10
Sb: #17744-#Subroutine modules
Fm: Graham Trott 100115,1075
To: Bob van der Poel 76510,2203 (X)

Bob --

I've used subroutine modules in CD-I, to extend the functionality of a standard
high-level package (kinda like HyperCard's XCMD).  I attach below an example
(to compute the size of a rectangle across the diagonal without using sqrt).
As far as I know it's difficult to have static storage; I use a mixture of
getting the caller to pass the addresses of variables, combined with
self-modifying code (purists may groan but it's OK in CD-I).  You might
alternatively employ a shared data module.

First, a special cstart module:

* Radial.a

    use  oskdefs.d

    psect  XCMD,(Sbrtn<<8)+Objct,(ReEnt<<8),1,0,Start

    org  -32768

_attop  do.l  1
_mtop:  do.l  1
_stbot:  do.l  1
errno:  do.l  1
_totmem:  do.l  1
_sbsize:  do.l  1
_fcbs:  do.l  1
environ:  do.l  1
_pathcnt: do.w  1
_sysglob: do.l  1

Start:  dc.l  Function-Start     Offset to the C main program

Params  dz.l  3        This is the self-modifying storage area

* This function returns the address of an item of storage,
* organized as an array of pointers to data (see the C code).

Parameter: lea  Params(pc),a0
    asl.l  #2,d0
    move.l (a0,d0),d0
    rts

    ends

Next, the C part of the subroutine module:

/* Radial.c */

extern long *Parameter();     /* returns the address of a parameter */

void Function()               /* the main entry point */
{
 long width, height, square, n;

 width=*(Parameter(0));       /* get the data from the first variable */
 height=*(Parameter(1));      /* ditto the second */
 square=width*width+height*height;

 for (n=2; n*n