From: Miles Bader <miles.bader@necel.com>
To: Thien-Thi Nguyen <ttn@gnuvola.org>
Cc: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>, emacs-devel@gnu.org
Subject: Re: Untagging by subtraction instead of masking on USE_LSB_TAG
Date: Mon, 28 Jan 2008 13:22:38 +0900 [thread overview]
Message-ID: <buotzkyd1f5.fsf@dhapc248.dev.necel.com> (raw)
In-Reply-To: <87ve5ezjwp.fsf@ambire.localdomain> (Thien-Thi Nguyen's message of "Mon, 28 Jan 2008 04:52:22 +0100")
Thien-Thi Nguyen <ttn@gnuvola.org> writes:
> For masking, i see offsets (lwz) of 4,0,0 (lines A,B,C).
> For subtraction, -1,-5,-5.
>
> It's very possible that the machine can handle 4,0,0 more
> efficiently; those all are even (0, modulo 2) and in two cases
> "nothing"! Furthermore, the maximum absolute offset for the
> subtraction method is 5, which is larger (faaarther away) than 4.
>
> Anyway, here is an excerpt from p.532 of "PowerPC 405, Embedded
> Processor Core, User's Manual":
Note that the important value here is the EA, not the offset. Typically
in a LSB tag scheme, the tags are arranged so that after adding these
"funny" offsets, the resulting EA is aligned properly.
-Miles
--
Apologize, v. To lay the foundation for a future offense.
next prev parent reply other threads:[~2008-01-28 4:22 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-28 2:07 Untagging by subtraction instead of masking on USE_LSB_TAG YAMAMOTO Mitsuharu
2008-01-28 3:52 ` Thien-Thi Nguyen
2008-01-28 4:22 ` Miles Bader [this message]
2008-01-28 4:25 ` Miles Bader
2008-01-28 5:02 ` YAMAMOTO Mitsuharu
2008-01-28 15:07 ` Stefan Monnier
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