🚀 go-pugleaf

struct REGPACK rp;  /* for the intr() call */
void interrupt myinthandler(ax,bx,cx,dx,bp,ds,es,flags)
{
  rp.r_ax=ax;
  rp.r_bx=bx;
  rp.r_cx=cx;
  rp.r_dx=dx;
  rp.r_bp=bp;
  /* plus other pointers and indexes as required */
  rp.r_ds=ds;
  rp.r_es=es;
  intr(old_ints_new_int_num, &rp);
  ax=rp.r_ax;
  bx=rp.r_bx;
  cx=rp.r_cx;
  dx=rp.r_dx;
  bp=rp.r_bp;
  ds=rp.r_ds;
  es=rp.r_es;
  flags=rp.r_flags;
}

The above is for Turbo-C.  Don't ask me how to convert it to other
C implementations.   The idea is simple.  You transfer the original
INT to a different location (just like the HD BIOS transfers the
FD INT 13H).  Then you use the REGPACK structure to move the information
that a particular ISR needs to the function and back.  Turbo-C
handles interrupt-functions very cleanly by pushing all registers
onto the stack;  thus it's easy to adjust the return values.  When
looking for a new place for the old ISR,  I routinely scan for an
empty location (0000:0000) in the area of INT 80H-FDH.  If DOS is
less than 3,  the vectors are not initialized and thus I just pick
F0H.

Some problems of the above code:  HUGE overhead as far as time,
HUGE stack requirement (if you count stack size in bytes).

Aki.
.

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