Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!hplabs!otter!sfk
From: sfk@otter.hple.hp.com (Stephen Knight)
Newsgroups: comp.lang.lisp
Subject: Re: The BEST way to sum a list
Message-ID: <1350018@otter.hple.hp.com>
Date: 1 Nov 88 10:28:33 GMT
References: <7559@megaron.arizona.edu>
Organization: Hewlett-Packard Laboratories, Bristol, UK.
Lines: 23

jcp@arizona.edu (John Peterson) writes:
> The discussion [comparing different ways to sum a list]
> ignores a basic limitation of Common Lisp: call-arguments-limit. 

A very good point!  I would be interested in the typical values of this
system parameter.  Poplog CL has a default call-arguments-limit of 
536870912.  Is this unusual?

> (There are some very good implementation reasons for this limit.  Using
> registers for parameter passing yields dramatic speedup, but only a
> finite number of registers or psuedo registers are available.)

Although this is an explanation, I don't think it is an acceptable 
justification for strange limits like 50.  Sure, there are only a finite 
number of registers.  When they are all used up another parameter passing
mechanism is required.  This does not seem to be especially impractical or
even difficult.

I am reminded of a similar case in Pascal, where the guaranteed maximum size
of a set is something like 64 -- which is a crippling limitation in terms of
guaranteed portability.  In these cases one has to make a choice based on the
actual limits of popular compilers.

Steve Knight