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From: dhesi@bsu-cs.UUCP (Rahul Dhesi)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Interesting 80X86 instruction
Message-ID: <929@bsu-cs.UUCP>
Date: Thu, 6-Aug-87 15:10:56 EDT
Article-I.D.: bsu-cs.929
Posted: Thu Aug  6 15:10:56 1987
Date-Received: Sat, 8-Aug-87 14:24:26 EDT
References: <767@custom.UUCP>
Reply-To: dhesi@bsu-cs.UUCP (Rahul Dhesi)
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 26

In article <767@custom.UUCP> boykin@custom.UUCP writes:
>Taking out my handy debugger I found that
>AAD *is* a one-byte instruction with the second byte acting
>as a parameter.  Try coding the following:
>
>	db	0d5h, 10h
>
>and you'll create an instruction which does:
>	AL = AL + (16 * AH)
>	AH = 0.
>
>. . . I'm sure someone
>will find a case where this is useful.  If you do, let me know!

When offering advice like this, please always be sure to include this
disclaimer:  "WARNING:  SOFTWARE TAKING ADVANTAGE OF THIS INFORMATION
WILL PROBABLY FAIL IN THE FUTURE."  Remember, naive users may not
realize this unless you tell them.

The above undocumented feature of the 8086 does not work on all
processors in the family.  Stick to documented instructions.  If you
can't resist the temptation of pushing you luck, at least refrain from
advising others to do the same without adequate warning of the folly of
this type of programming technique.
-- 
Rahul Dhesi         UUCP:  {ihnp4,seismo}!{iuvax,pur-ee}!bsu-cs!dhesi