From: Andy Walker <jawalker@stl.quik.com>
To: Michael Meissner <meissner@cygnus.com>
Cc: Zack Weinberg <zackw@stanford.edu>,
GCC general mailing list <gcc@gcc.gnu.org>
Subject: Re: Hashing of "switch/case" selections
Date: Sun, 07 Jan 2001 18:37:00 -0000 [thread overview]
Message-ID: <3A59286B.D0395F63@stl.quik.com> (raw)
In-Reply-To: <20010105135428.B2417@cse.cygnus.com>
Interesting comment. I will take it into account.
Andy
Michael Meissner wrote:
> On Thu, Jan 04, 2001 at 01:39:10AM -0800, Zack Weinberg wrote:
> > On Wed, Dec 27, 2000 at 10:43:40PM -0600, Andy Walker wrote:
> > [much interesting stuff]
> > > My experience as a programmer is that programs are almost never written
> > > with switches to more than a few hundred cases. I personally have never
> > > seen one. More than that, and the programmer finds a more efficient,
> > > more readable, more maintainable solution, and he can do so because he
> > > has a deep knowledge of the problem that is unavailable to the
> > > compiler. My seat-of-pants estimate is that 400 cases is a good, maybe
> > > even high, maximum for Hash evaluations. A program containing a switch
> > > statement with more than 400 cases in it probably has enough other
> > > severe design problems that it will never be worth running anyway.
> >
> > This is true in my experience for code written by humans, but not
> > necessarily for machine-generated code. Take a look at insn-attrtab.c
> > in your GCC build directory, or at cp/parse.c in the source tree.
>
> Some of the simulators in the gdb releases have the ability to build very giant
> switch tables to speed up decoding machine instructions, though we haven't
> built them with the largest tables in quite some time, because the compiler's
> memory was going into the gigabytes.
>
> At a former job, I recall hearing that they had built a profiler/simulator for
> the machine, and used a completely dense 65k element switch table.
>
> --
> Michael Meissner, Red Hat, Inc. (GCC group)
> PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
> Work: meissner@redhat.com phone: +1 978-486-9304
> Non-work: meissner@spectacle-pond.org fax: +1 978-692-4482
next prev parent reply other threads:[~2001-01-07 18:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-12-27 20:41 Andy Walker
2000-12-27 21:33 ` I have found an ICE Magnus Fromreide
2001-01-01 14:30 ` Hashing of "switch/case" selections Nix
2001-01-04 1:39 ` Zack Weinberg
2001-01-05 10:54 ` Michael Meissner
2001-01-07 18:37 ` Andy Walker [this message]
2001-01-07 18:12 ` Andy Walker
2000-12-28 7:15 Robert Dewar
2000-12-28 21:06 ` Dave Korn
2000-12-28 7:19 Robert Dewar
2000-12-28 21:10 dewar
2000-12-28 22:41 ` Dave Korn
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