Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 beta 3/9/83; site uthub.UUCP
Path: utzoo!utcsrgv!utai!uthub!thomson
From: thomson@uthub.UUCP (Brian Thomson)
Newsgroups: net.lang.c
Subject: Re: setjmp/longjmp
Message-ID: <190@uthub.UUCP>
Date: Fri, 2-Nov-84 16:30:55 EST
Article-I.D.: uthub.190
Posted: Fri Nov  2 16:30:55 1984
Date-Received: Fri, 2-Nov-84 20:42:40 EST
References: <1@imd.UUCP>
Organization: CSRG, University of Toronto
Lines: 18

While I agree that setjmp/longjmp SHOULD behave according to Gospel,
I have a great deal of sympathy for the implementation designer
who doesn't want to sacrifice the efficiency of his calling sequence
for the sake of longjmp.

There is a similar issue of whether to use a stack frame pointer.
Your call/return sequence will be faster if you don't, and you can
address everything relative to the sp.  All the frame pointer
buys you is the ability to get a calling trace from your favourite
core image debugger.  Is it worth it?

Some 780 instruction timings I did years ago indicated that the
CALLS/RET pair take ~15 microseconds minimum, while JSR/RTS execute
in 3.  That's a big penalty for the sake of setjmp(), calling traces,
and, oh yes, the infamous nargs().
-- 
		    Brian Thomson,	    CSRI Univ. of Toronto
		    {linus,ihnp4,uw-beaver,floyd,utzoo}!utcsrgv!uthub!thomson