Date: Mon, 1 Sep 1997 08:25:20 -0700 (PDT)
Message-Id: <199709011525.IAA07160@adit.ap.net>
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To: Temujin <temujin AT sentex DOT net>, djgpp AT delorie DOT com
From: Nate Eldredge <eldredge AT ap DOT net>
Subject: Re: Dos Version 6.20 and 6.21
Precedence: bulk

At 12:33  8/25/1997 -0700, Temujin wrote:
>Andrew Happ wrote:
>>   XCHG   AH,AL
>>   XOR     AH,AH
>
>This basically acomplishes nothing, if AL is moved into AH and then
>zeroed out, the XCHG line is an extra useless line.
Sorry, you're wrong. The previous contents of AH are preserved in the AL
register. XCHG works both ways, remember?
Now, it's true that the XCHG could have been replaced with a MOV, which
would have been clearer. Maybe on some flavor of processor the XCHG executes
one cycle faster, or something. I don't know.

PS. What is this doing on this newsgroup, anyway?

Nate Eldredge
eldredge AT ap DOT net