Execution on Z80 CPM or DOS+ systems

The code in BUFFLIB is all executable on 8080s, and thus will never
disturb the extended registers on Z80s (af', bc', de', hl') nor the
index registers (ix, iy). The main program is thus ALMOST perfectly
free to use these.

HOWEVER, some poor bios implementations DO disturb these registers.
The bios  is never used except  through BDOS calls  (or direct bios
calls,  not considered here).   Thus the system can be protected at
one central point (.DOS in BUFFLIB).   DOSZ is a replacement module
for this purpose.

Known examples of  poor bios implementations are the Osborne I  and
the original Kaypro 2/4. A replacement Kaypro bios/rom (83 version)
is available. 

To use,  simply alter the linking procedure  to include DOSZ module
at any time before the library search.  E.G.,  if the original link
command was:

         ... myprog,bufflib/s ...
use
         ... myprog,dosz,bufflib/s ...

(... represents any other components of the command)

The resultant program will execute on 8080s and z80s  (at least the
library portions).  Results on the 8085 and NEC V20 are unknown.

Even worse are  systems that disturb these registers on interrupts.
No cure is available except to disable interrupts whenever the alt-
ernate registers are vulnerable.   BUFFLIB routines are intended to
be  usable  as components of  interrupt systems,  and enable inter-
rupts to control critical data access, so this will fail unless the
appropriate modules are modified.


NOTE: At some future time I intend to include the high speed  32x32
bit multiply/divide routines, which execute ONLY on Z80s.  These do
not permanently disturb the alternate registers,  although register
IX is used, so most comments above apply.   At a 2 Mhz clock multi-
plication takes about 1.1 Millisec. for a 64 bit result.   The code
is again pure and re-entrant.

NOTE: If DOS+ is  in use the IX and IY registers  are automatically
protected against the bios.  This leaves only the alternate set.

      CBF.