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From: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Newsgroups: comp.os.msdos.programmer,comp.sys.ibm.pc.misc
Subject: Re: TASM bug? (no, not at all)
Message-ID: <8051@tekgvs.LABS.TEK.COM>
Date: 5 Sep 90 13:53:36 GMT
References: <4691@bdt.UUCP> <38580@shemp.CS.UCLA.EDU> <2953@amc-gw.amc.com>
Reply-To: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Followup-To: comp.os.msdos.programmer
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Organization: Tektronix, Inc., Beaverton,  OR.
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In article <2953@amc-gw.amc.com> jwbirdsa@europa.amc.com (James Birdsall) writes:
>
> In article <38580@shemp.CS.UCLA.EDU> wales@CS.UCLA.EDU (Rich Wales) writes:
> >[Discusses using CBW or XOR to load 8 bit data into 16 bit registers]

>   There's also MOVZX, an obscure instruction that is available on all 80x86.
[...]
>   Unfortunately, the complementary instruction (MOVSX, move with sign
>extend) is only available on the 386.

MOVZX and MOVSX are only in the 80386 or later (80486).

Compared to MOV followed by CBW, length is the same, and 1 clock is saved
(for either processor). Compared to MOV followed by XOR, 1 byte is saved
but no clocks (one clock longer for 80486!). I only use these in 80386
protected mode programs because they are clearer.

Tom Almy
toma@tekgvs.labs.tek.com
Standard Disclaimers Apply