🚀 go-pugleaf

In article <443@anasaz.UUCP> john@anasaz.UUCP (John Moore) writes:
   I found the ability to define multiple stacks to be very handy.
   A FORTH interpreter can be written in that instruction set that
   is very efficient. Also, I once wrote a binary tree balancing routine
   that used a pair of recursive co-routines. It took about 30
   instructions for both routines. Try that with today's architectures! 

The 680x0 can use any of its 8 address registers as stack pointers for
data.  The only thing that makes its "stack pointer" register special
is that the hardware uses it for subroutine calls, interrupts, etc.
If you want to use one of the other stack pointers for flow control,
you have to do it with an instruction sequence:

; Call subroutine using A0 as a stack.
	move.l	#1f,-(a0)
	bra	subroutine
1f:

; Return from subroutine through A0 (trashes a register)
	move.l	(a0)+,a1
	jmp	(a1)

In other words, a FORTH interpreter could be made as efficient on the
680x0, but the binary tree balancing routine might take a little more
work.

I like the way the PDP-11 treats the program counter as a general
register.  You can play a lot of tricks with that!
-- 
	Bruce Robertson
	Hundred Acre Software, Reno, NV
	Domain: bruce@pooh.com
	UUCP:   ...!uunet!tahoe.unr.edu!heather!bruce