Jax4th for the Commodore Amiga is Copyright 1991, 1993, 1994 Jack J. Woehr
This is free software, and may be redistributed under certain conditions.
See the file COPYING.TXT for more information. Jax4th comes with ABSOLUTELY
NO WARRANTY

Jax4th Internals
----------------

Execution Tokens

All execution tokens are thirty-two bits and are passed in the form

	(K|(offset>>1))

where K, bit D31 of the token, if set indicates that the execution
token refers to the kernel and if not set indicates that the execution
token refers to the local code image; and where (offset>>1) is the
offset of the execution body in the given image logically shifted
right one bit.

Kernel Addresses

Kernel addresses are thirty-two bits and are passed as offsets from
the address pointed to by the Code Pointer (CP). As the kernel is
re-entrant, all data addresses used by the kernel refer to the same
local data section as those referenced by the local code image.

Local Code Addresses

Addresses in the Local Code Image are thirty-two bits and are passed
as offsets from the address pointed to by the Next Pointer (NP). The
beginning of the local code image contains a copy of the NEXT routine.

Data Addresses

Data addresses are thirty-two bits and are passed as offsets from
the address pointed to by the Base Pointer (BP). As the kernel is
re-entrant, all data addresses used by the kernel refer to the same
local data section as those referenced by the local code image.

Stack Addresses

Each time a reentrant resident program is invoked, the AmigaDOS
loader gives it its own stack, usually of about 4000 bytes. In JAX4TH,
a portion of this stack is consumed by startup overhead. The rest is
divided approximately equally between return stack and data stack.
Forth Top of Data Stack is cached in D7 (TOS) and the rest of the
stack is pointed to by A7 (DSP). A6 is the Return Stack Pointer (RP).
Forth words referencing the addresses contained in the stack pointers
consume and return Data Segment relative addresses. Of course, the
stack pointers themselves contain machine addresses.

Instruction Pointer

The Forth Instruction Pointer contains a machine address. NEXT examines each
instruction as fetched from the cell currently pointed at by IP and decides
if the token contained therein is a resident-kernel-relative address or a
local-code-relative address before branching.

NEST preserves the current IP on the Return Stack and reloads IP with
a machine address.