Path: utzoo!attcan!uunet!mcvax!ukc!etive!aiva!jeff
From: jeff@aiva.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.lisp
Subject: Re: Franz-lisp from Sun User's Group bug fix
Keywords: arrays, sun, franz-lisp
Message-ID: <582@aiva.ed.ac.uk>
Date: 11 Sep 88 17:34:56 GMT
References: <465@sce.UUCP>
Reply-To: jeff@uk.ac.ed.aiva (Jeff Dalton)
Organization: Dept. of AI, Univ. of Edinburgh, UK
Lines: 43

In article <465@sce.UUCP> fred@sce.UUCP (Fred J. Kaudel) writes:
>Hello, Franz-lisp version 38.92 as distributed from the Sun User's Group
>distribution tape number 2 [...]

>-has anyone found a fix for the zerop bug in compiled lisp code on the suns?
> More specifically, (zerop 0) and (zerop 0.0) both evaluate to t on the vax,
> but evaluate to t and nil, respectively, when compiled on the sun using
> Liszt version 8.39a (comes with lisp on the tape).  This problem is
> quite irritating since it makes code non-portable.

Well, I've fixed it, and I know someone else has too because I've seen
two different fixes.  My fix looks somewhat suspect, I know, but is
not actually worse than similar code elsewhere in Liszt.

The problem is in cm-zerop in liszt/func.l.  The comment below will
make sense if you look at (1) the VAX code, (2) the current definition
of cm-zerop, and (3) the code for cm-=& in liszt/fixnum.l.

; [begin jwd]  The trick has to be a bit different on the 68k than on the
; VAX because the NULL test doesn't work unless NIL is at address zero.
; However, expanding (zerop x) as (=& 0 x) won't work either, because
; =& will compile this as an address comparison and not all floating
; zeros have the same address (much less the address of fixed 0).
; Therefore, we have to do some explicit dereferencing, just as =&
; does in the general case.  Then (zerop x) expands, modulo bignums,
; to (eq (cdr 0) (cdr x)).

#+for-68k
(defun cm-zerop nil
   (cond ((atom (cadr v-form))
	  `(and (eq (cdr 0) (cdr ,(cadr v-form)))
		(not (bigp ,(cadr v-form)))))
	 (t (let ((gnsy (gensym)))
		`((lambda (,gnsy)
		      (and (eq (cdr 0) (cdr ,gnsy))
			   (not (bigp ,gnsy))))
		  ,(cadr v-form))))))

; [end jwd]

Jeff Dalton,                      JANET: J.Dalton@uk.ac.ed             
AI Applications Institute,        ARPA:  J.Dalton%uk.ac.ed@nss.cs.ucl.ac.uk
Edinburgh University.             UUCP:  ...!ukc!ed.ac.uk!J.Dalton