Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!iuvax!rutgers!mcnc!ecsvax!dukeac!sbigham
From: sbigham@dukeac.UUCP (Scott Bigham)
Newsgroups: comp.lang.c
Subject: Re:  info-c digest v2n226
Message-ID: <1075@dukeac.UUCP>
Date: 3 Nov 88 00:42:34 GMT
References: <8810242200.AA05011@lti.com>
Reply-To: sbigham@dukeac.UUCP (Scott Bigham)
Organization: Academic Computing, Duke University, Durham, NC
Lines: 28

In article <8810242200.AA05011@lti.com> reg@lti.com (Rick Genter x18) writes:
>The difference [between hardware and software stacks]
>is that a machine with a hardware stack can dereference
>the top of the stack and modify the stack pointer as an atomic operation
>(usually via an addressing mode).  A machine with "only" software stacks
>must use multiple machine instructions to perform this operation...

What of the 68000?  By your argument, it has a hardware stack, since I can
push something onto the stack with MOVE.L #FFFF,-(SP).  But suppose I
allocate a chunk of memory and set another address register (say A3) to the
top of it.  Then I can say MOVE.L #FFFF,-(A3) et al; essentially, I've just
produced my own stack out of thin air.  I would call this a software stack,
since it wasn't there when I turned the machine on.  But then why isn't the
SP-based stack a software stack?  (Remember, SP is just A7)

Just to add my <= $0.02, I would say that a machine has a hardware stack if
you have to go through a bunch of ugly machinations to implement your own
stack; otherwise, it has a software stack.

Someone more net-knowledgeable than myself may wish to redirect followups
elsewhere.  I would if I knew where to.

						sbigham

-- 
Scott Bigham                         "The opinions expressed above represent
Internet sbigham@dukeac.ac.duke.edu   me and everyone that agrees with me.
USENET   sbigham@dukeac.UUCP          If that includes Duke University,
...!mcnc!ecsgate!dukeac!sbigham       I'll be amazed."