From: Alexandre Oliva <aoliva@redhat.com>
To: Kevin Lawton <kevinlawton2001@yahoo.com>
Cc: Robert Dewar <dewar@gnat.com>, gcc@gcc.gnu.org
Subject: Re: Request of new __attribute__ for switch statements (elimination of the bounds check)
Date: Sat, 12 Oct 2002 10:43:00 -0000 [thread overview]
Message-ID: <or4rbsi8uc.fsf@free.redhat.lsd.ic.unicamp.br> (raw)
In-Reply-To: <20021011202232.85226.qmail@web80303.mail.yahoo.com>
On Oct 11, 2002, Kevin Lawton <kevinlawton2001@yahoo.com> wrote:
> I haven't tried turning the last case into the default, but I
> can't see how that eliminates a check, so I'm not clear on the
> win there.
it (kind of) turns:
if (x == 255) goto case_255;
...
else if (x == 0) goto case_0;
else /* do nothing */;
into
if ((unsigned)x >= 255) goto case_255;
...
else if (x == 0) goto case_0;
Admittedly, this is still not as efficient as the compiler knowing
that x is in [0,255] and just loading the jump from a jump table, but
it's already some improvement.
--
Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer aoliva@{redhat.com, gcc.gnu.org}
CS PhD student at IC-Unicamp oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist Professional serial bug killer
next prev parent reply other threads:[~2002-10-12 4:23 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-10-11 13:22 Robert Dewar
2002-10-11 15:12 ` Kevin Lawton
2002-10-12 10:43 ` Alexandre Oliva [this message]
-- strict thread matches above, loose matches on Subject: below --
2002-10-16 9:19 Robert Dewar
2002-10-15 22:40 Robert Dewar
2002-10-15 23:57 ` Zack Weinberg
2002-10-15 6:43 Mattias Engdegård
2002-10-11 13:20 Kevin Lawton
2002-10-12 4:18 ` Ralph Loader
2002-10-14 8:31 ` Richard Zidlicky
2002-10-14 10:09 ` Dale Johannesen
2002-10-14 21:11 ` Jamie Lokier
2002-10-14 22:01 ` Zack Weinberg
2002-10-15 8:12 ` Michael Matz
2002-10-15 19:15 ` Zack Weinberg
2002-10-15 19:18 ` Dale Johannesen
2002-10-16 14:07 ` Richard Henderson
2002-10-15 21:16 ` Kevin Lawton
2002-10-15 23:40 ` Tim Hollebeek
2002-10-16 3:40 ` Michael Matz
2002-10-16 13:38 ` Tim Hollebeek
2002-10-16 14:23 ` Michael Matz
2002-10-16 13:27 ` Hartmut Schirmer
2002-10-16 3:25 ` Joseph S. Myers
2002-10-16 7:57 ` Fergus Henderson
2002-10-16 11:19 ` Daniel Jacobowitz
2002-10-15 7:54 ` Michael Matz
2002-10-15 13:29 ` Jamie Lokier
2002-10-15 14:06 ` Kevin Lawton
2002-10-15 15:32 ` Jamie Lokier
2002-10-15 14:28 ` Michael Matz
2002-10-15 15:19 ` Jamie Lokier
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=or4rbsi8uc.fsf@free.redhat.lsd.ic.unicamp.br \
--to=aoliva@redhat.com \
--cc=dewar@gnat.com \
--cc=gcc@gcc.gnu.org \
--cc=kevinlawton2001@yahoo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).