Re: Assembler Macros

On Sun, 24 Jun 2007 22:22:20 -0400 "John W. Kennedy" <jwkenne@xxxxxxxxxxxxx>
wrote:

:>Binyamin Dissen wrote:
:>> On Sun, 24 Jun 2007 12:53:03 +0200 "Sven Pran" <no.direct@xxxxxxxxxxxx> wrote:

:>> :>Never use ST in situations like this (when the alignment of &FLD
:>> :>is unknown), use STCM instead:

:>> :> STCM 1,B'1111',&FLD

:>> Checks his watch. Yes, it is 2007.

:>> This has not been an issue since the 370.

:>...which introduced the STCM instruction.

Among many others.

The purpose of STCM was not to do an unaligned store. It was to allow a
selective store of certain bytes in a register.

:>> There are very few instructions which require alignment.

:>The assembler error message for bad alignment still occurs, and if you
:>suppress it arbitrarily, you can lose performance in other places.

Don't make the assumption that register operations alone lose performance if
not aligned.

For example, unless one aligns the source and target of an MVC at the same
relative byte in a doubleword one loses performance.

--
Binyamin Dissen <bdissen@xxxxxxxxxxxxxxxxxx>
http://www.dissensoftware.com

Director, Dissen Software, Bar & Grill - Israel


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