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From: Stephen Fuld <sfuld@alumni.cmu.edu.invalid>
Newsgroups: comp.arch
Subject: Re: is Vax addressing sane today
Date: Wed, 25 Sep 2024 12:30:02 -0700
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On 9/24/2024 10:57 AM, MitchAlsup1 wrote:
> On Tue, 24 Sep 2024 17:06:27 +0000, Stephen Fuld wrote:
> 
>> On 9/23/2024 11:02 PM, Terje Mathisen wrote:
>>
>> snip
>>
>>> Maybe all add/sub/etc opcodes that are immediately followed by an INTO
>>> could be fused into a single ADDO/SUBO/etc version that takes zero extra
>>> cycles as long as the trap part isn't hit?
>>
>> If you are going to do that, why not make it an optional prefix byte?
>> That way, no fusion needed, no extra cycles, yet the same amount of code
>> space.
> 
> Realistically, what is the difference if INTO is a prefix
> byte or a postfix byte ?

Of course, IANAHG, but my guess was that not having to do instruction 
fusion was worth something, and my suggestion has zero cost.  If this is 
wrong, then there is no difference.




-- 
  - Stephen Fuld
(e-mail address disguised to prevent spam)