From: John Prevost <jmp@arsdigita.com>
To: eijiro_sumii@anet.ne.jp
Cc: checker@d6.com, caml-list@inria.fr, gerd@gerd-stolpmann.de,
sumii@venus.is.s.u-tokyo.ac.jp
Subject: Re: substring match like "strstr"
Date: 12 Dec 2000 20:12:09 -0500 [thread overview]
Message-ID: <87ofyhw2dy.fsf@elbereth.pgh.arsdigita.com> (raw)
In-Reply-To: <20001212122807K.sumii@yl.is.s.u-tokyo.ac.jp>
>>>>> "es" == eijiro sumii <eijiro_sumii@anet.ne.jp> writes:
>> Any ideas why strstr blows the others away? What's the libc
>> strstr look like?
es> I have no idea, unfortunately...
I just grabbed the glibc version, and found the following comment at
the head of it:
/*
* My personal strstr() implementation that beats most other algorithms.
* Until someone tells me otherwise, I assume that this is the
* fastest implementation of strstr() in C.
* I deliberately chose not to comment it. You should have at least
* as much fun trying to understand it, as I had to write it :-).
*
* Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
Since the text of the function involves not only nasty gotos
(particularly frightening is "goto shloop;" but also pointer tricks
and register declarations, I'd say it's to be expected that it'll
outperform O'Caml. I am, however, seeing if I can figure out the
essential algorithm used (if there's really anything smart to it) and
will let you know if I come up with anything extra special.
The file strstr.c is included below for your edification. I'd argue
that any Caml version is likely to a be a wee bit easier to
understand.
John.
/* Return the offset of one string within another.
Copyright (C) 1994, 1996, 1997 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
/*
* My personal strstr() implementation that beats most other algorithms.
* Until someone tells me otherwise, I assume that this is the
* fastest implementation of strstr() in C.
* I deliberately chose not to comment it. You should have at least
* as much fun trying to understand it, as I had to write it :-).
*
* Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
#if HAVE_CONFIG_H
# include <config.h>
#endif
#if defined _LIBC || defined HAVE_STRING_H
# include <string.h>
#endif
typedef unsigned chartype;
#undef strstr
char *
strstr (phaystack, pneedle)
const char *phaystack;
const char *pneedle;
{
register const unsigned char *haystack, *needle;
register chartype b, c;
haystack = (const unsigned char *) phaystack;
needle = (const unsigned char *) pneedle;
b = *needle;
if (b != '\0')
{
haystack--; /* possible ANSI violation */
do
{
c = *++haystack;
if (c == '\0')
goto ret0;
}
while (c != b);
c = *++needle;
if (c == '\0')
goto foundneedle;
++needle;
goto jin;
for (;;)
{
register chartype a;
register const unsigned char *rhaystack, *rneedle;
do
{
a = *++haystack;
if (a == '\0')
goto ret0;
if (a == b)
break;
a = *++haystack;
if (a == '\0')
goto ret0;
shloop: }
while (a != b);
jin: a = *++haystack;
if (a == '\0')
goto ret0;
if (a != c)
goto shloop;
rhaystack = haystack-- + 1;
rneedle = needle;
a = *rneedle;
if (*rhaystack == a)
do
{
if (a == '\0')
goto foundneedle;
++rhaystack;
a = *++needle;
if (*rhaystack != a)
break;
if (a == '\0')
goto foundneedle;
++rhaystack;
a = *++needle;
}
while (*rhaystack == a);
needle = rneedle; /* took the register-poor approach */
if (a == '\0')
break;
}
}
foundneedle:
return (char*) haystack;
ret0:
return 0;
}
next prev parent reply other threads:[~2000-12-14 18:20 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-12-08 6:04 eijiro_sumii
2000-12-08 12:57 ` Gerd Stolpmann
2000-12-10 13:16 ` eijiro_sumii
2000-12-10 15:39 ` Gerd Stolpmann
2000-12-11 3:57 ` eijiro_sumii
2000-12-12 13:58 ` Julian Assange
2000-12-11 21:07 ` Chris Hecker
2000-12-11 22:22 ` Gerd Stolpmann
2000-12-12 5:06 ` Chris Hecker
2000-12-12 12:28 ` Jean-Christophe Filliatre
2000-12-13 10:02 ` eijiro_sumii
2000-12-13 10:17 ` Eijiro Sumii
2000-12-13 10:53 ` Julian Assange
2000-12-13 13:28 ` Eijiro Sumii
2000-12-12 3:28 ` eijiro_sumii
2000-12-13 1:12 ` John Prevost [this message]
2000-12-13 2:35 ` Chris Hecker
2000-12-12 10:07 ` Sven LUTHER
2000-12-14 3:36 ` eijiro_sumii
2000-12-14 6:48 ` Chris Hecker
2000-12-14 8:02 ` eijiro_sumii
2000-12-14 21:53 ` Stephan Tolksdorf
2000-12-14 21:12 Ruchira Datta
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=87ofyhw2dy.fsf@elbereth.pgh.arsdigita.com \
--to=jmp@arsdigita.com \
--cc=caml-list@inria.fr \
--cc=checker@d6.com \
--cc=eijiro_sumii@anet.ne.jp \
--cc=gerd@gerd-stolpmann.de \
--cc=sumii@venus.is.s.u-tokyo.ac.jp \
/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 NNTP newsgroup(s).