I generally go for the code that
Is easy to read
Uses the least storage
Does not require a literal or named constant
MVHHI is six bytes and clear; the alternatives obscure the intent and none is
shorter.
--
Shmuel (Seymour J.) Metz
http://mason.gmu.edu/~smetz3
עַם יִשְׂרָאֵל חַי
נֵ֣צַח יִשְׂרָאֵ֔ל לֹ֥א יְשַׁקֵּ֖ר
________________________________________
From: IBM Mainframe Assembler List <[email protected]> on behalf
of Charles Mills <[email protected]>
Sent: Monday, February 9, 2026 1:54 PM
To: [email protected] <[email protected]>
Subject: Re: Half-word Counter in Storage -- Best Practice
External Message: Use Caution
The differences in CPU time are so minute as to be insignificant.
The big hit is bringing the counter in and out of cache, which is the
same any way you do it.
I like the last, because it is the clearest code -- the instructions
correspond to what you are doing logically: setting a counter to a
numeric zero.
/Charles/
On 2/9/2026 10:48 AM, David Clark wrote:
> If a half-word counter has to be in storage (to save on registers) and must
> start at zero, which is better or which would you prefer to do as a best
> practice?
>
> ...simply clear storage?
>
> XC STRGLEN,STRGLEN FOR USED STRING LENGTH COUNTER
>
> ...or clear a register and save to storage?
>
> XR R5,R5 STARTING AT ZERO
> STH R5,STRGLEN SET USED STRING LENGTH COUNTER
>
> ...or use an immediate value and save to storage?
>
> LHI R5,0 STARTING AT ZERO
> STH R5,STRGLEN SET USED STRING LENGTH COUNTER
>
> Sincerely,
>
> Dave Clark
> --
> int.ext: 91078
> direct: (937) 531-6378
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>
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--
/Charles/
+1-707-291-0908
