On Mon, Feb 17, 2014 at 11:36 AM, Ted MacNEIL <eamacn...@yahoo.ca> wrote:
> I have to ask: Why they big concern over a few instructions?
> Optimisation of a few is not worth the
> effort these days.
>
>
> -
> -teD
> -
>
OK, this then causes me to wonder why IBM has bothered to create
instructions such as "Load On Condition" and "Store On Condition". The
manual in the STOC says:
<quote>
STORE ON CONDITION provides a function
similar to that of a separate BRANCH ON CONDITION
instruction followed by a STORE instruction,
except that STORE ON CONDITION does
not provide an index register. For example, the
following two instruction sequences are equivalent.
STOCG 15,256(7),8 BC 7,SKIP
STG 15,256(7)
SKIP DS 0H
On models that implement predictive branching,
the combination of the BRANCH ON CONDITION
and STORE instructions may perform
somewhat better than the STORE ON CONDITION
instruction when the CPU is able to successfully
predict the branch condition. However,
on models where the CPU is not able to successfully
predict the branch condition, such as when
the condition is more random, the STORE ON
CONDITION instruction may provide significant
performance improvement.
</quote>
The above makes me wonder if my example of using the BPRP (does anyone else
read that as "burper"?) instruction, since I _know_ at that point that the
branch _will be_ taken should be used instead of the STOC.
--
Wasn't there something about a PASCAL programmer knowing the value of
everything and the Wirth of nothing?
Maranatha! <><
John McKown
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