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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: 80286 protected mode
Date: Sat, 12 Oct 2024 18:32:48 +0000
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On Sat, 12 Oct 2024 5:06:05 +0000, Brett wrote:

> MitchAlsup1 <mitchalsup@aol.com> wrote:
>> On Fri, 11 Oct 2024 12:10:13 +0000, David Brown wrote:
>>
>>>
>>> Do you think you can just write this :
>>>
>>> void * memmove(void * s1, const void  * s2, size_t n)
>>> {
>>> return memmove(s1, s2, n);
>>> }
>>>
>>> in your library's source?
>>
>>       .global memmove
>> memmove:
>>       MM     R2,R1,R3
>>       RET
>>
>> sure !
>>
>
> Can R3 be a const, that causes issues for restartability, but branch
> prediction is easier and the code is shorter.

The 3rd Operand can, indeed, be a constant.
That causes no restartability problem when you have a place to
store the current count==index, so that when control returns
and you re-execute MM, it sees that x amount has already been
done, and C-X is left.
>
> Though I guess forwarding a const is probably a thing today to improve
> branch prediction, which is normally HORRIBLE for short branch counts.

That is what Predication is for.