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From: perkins@bnrmtv.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: NOP
Message-ID: <2695@bnrmtv.UUCP>
Date: Fri, 2-Oct-87 15:27:41 EDT
Article-I.D.: bnrmtv.2695
Posted: Fri Oct  2 15:27:41 1987
Date-Received: Sun, 4-Oct-87 01:33:56 EDT
References: <2306@sphinx.uchicago.edu> <4478@amd.AMD.COM> <6375@ut-ngp.UUCP>
Organization: BNR Inc., Mountain View, California
Lines: 14
Keywords: NOP

In article <6375@ut-ngp.UUCP>, ayac071@ut-ngp.UUCP (William T. Douglass) writes:
> Actually, I thought that NOPs did an OR of the AX register on itself (or some
> similar operation that causes no change to data.)

ORing a register with itself sets the flags.  OR AX,AX is the
simplest way of determining if AX is positive, negative, or zero.

NOP is XCHG AX,AX.  Since XCHG doesn't affect flags, this actually
causes no data to change.
-- 
{hplabs,amdahl,ames}!bnrmtv!perkins         --Henry Perkins

It is better never to have been born.  But who among us has such luck?
One in a million, perhaps.