Path: utzoo!attcan!uunet!cs.utexas.edu!swrinde!emory!mephisto!mcnc!rti!dg-rtp!gen-rtx!wood
From: wood@gen-rtx.rtp.dg.com (Tom Wood)
Newsgroups: comp.sys.m88k
Subject: Re: Grabbing arithmetic overflow traps ?
Message-ID: <1990Jun27.173213.8250@dg-rtp.dg.com>
Date: 27 Jun 90 17:32:13 GMT
References: <9724@discus.technion.ac.il> <3418@oakhill.UUCP>
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Organization: Data General Corporation, Research Triangle Park, NC
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In article <3418@oakhill.UUCP> shebanow@oakhill.UUCP (Mike Shebanow) writes:

> The 88k "add" and "sub" instructions do check for arithmetic overflow
> automatically.  I also have an Aviion; I replaced an "addu" instruction
> with an "add" in a piece of test code and purposely generated an
> overflow with the add.  The result was a floating point exception.
> You can catch this with your own handler w/o modifying the kernel.
> Unfortunately, looking at the gcc man page (online), I saw no way to
> get the compiler to generate "add" instead of "addu" when performing ops
> on signed integers (unless I overlooked something in the man page).
> Does anyone at DG know how to do this?

It wouldn't be too hard to change the `key' uses of addu/subu in the GCC
compiler to add/sub, but unfortunately, you would no longer have a C
compiler.  Perhaps that's too strong a statement, but in C, you typically
don't get integer overflow checks, and most often you don't want them.
---
			Tom Wood	(919) 248-6067
			Data General, Research Triangle Park, NC
			{the known world}!rti!xyzzy!wood, wood@dg-rtp.dg.com