Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!hpcc05!hpyhde4!hpycla!hpcuhc!hpcupt3!dhandly
From: dhandly@hpcupt3.cup.hp.com (Dennis Handly)
Newsgroups: comp.sys.hp
Subject: Re: HP9000-7XX overflow : Technical question
Message-ID: <48580012@hpcupt3.cup.hp.com>
Date: 6 Apr 91 07:53:21 GMT
References: <9934@discus.technion.ac.il>
Organization: Hewlett-Packard Cal Language Lab
Lines: 16

>How do I do integer overflow detection on PA-RISC? (using machine code is OK)
>Is it possible? Is it "cheap"? can it be done? can it be done without
>using a whole signal call mechanism every time an overflow occurs?

The add and subtract instructions have completers.  You can nullify 
the next instruction if a condition is/isn't meet.  Just make sure you
don't use the ADDO or SUBO unless you want to trap.

>Without this flag, or some other simple
>integer overflow detection method (that is "cheap") I will have
>to embed generated code that will test for overflow conditions on
>every simulated instruction (instead of a simple flag check).

Is the above two instructions for every add/subtract cheap enough?

Of course if you don't have overflows often, you might just want to trap.