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From: brian@neptune.AMD.COM (Brian McMinn)
Newsgroups: comp.arch
Subject: Arithmetic Traps in 29000
Message-ID: <490@neptune.AMD.COM>
Date: Wed, 18-Nov-87 22:56:59 EST
Article-I.D.: neptune.490
Posted: Wed Nov 18 22:56:59 1987
Date-Received: Sat, 21-Nov-87 13:40:16 EST
References: <1656@geac.UUCP> <863@winchester.UUCP> <197@m2.mfci.UUCP> <902@mips.UUCP> <8933@utzoo.UUCP> <6743@apple.UUCP> <3440@ames.arpa>
Reply-To: brian@neptune.AMD.COM (Brian McMinn)
Organization: Advanced Micro Devices, Inc., Austin, Texas
Lines: 21

In article <3440@ames.arpa> lamaster@ames.UUCP (Hugh LaMaster) writes:
>Do the "trap" type instructions interact with a mask in the user context
>which sets which conditions will trap

The Am29000 add/subtract instructions only check for the specific kind
of "wrongness" that is peculiar to that type of add or subtract.  In all
cases, the trap is taken if the answer is "wrong".  For example, the adds
(add signed) operation will trap if the correct result would not fit into
a 32-bit signed integer.  The addu (add unsigned) operation will trap if
the correct result would not fit into an unsigned 32-bit integer.  The
add (add and don't ask dumb questions :-) operation performs no checking.

Using these instructions, the user can specify the proper form of overflow
checking on an operation by operation basis (even finer granularity than
having a user register keep track of whether to trap on Overflow or Carry).

	brian@neptune.amd.com
-- 
	Brian McMinn		brian@neptune.AMD.COM
	Advanced Micro Devices
	Austin, Texas		1-(512)-462-5389