76661c1ce5
It is O(n) in the length of the haystack (big) string, and has special cases for short needle (little) strings, of one to four bytes, to avoid excessive overhead. There are a small set of nearly trivial cases where the startup overhead of the musl implementation makes it slightly slower -- for example, a 31 byte needle that matches the beginning of the haystack. It's faster for non-trivial cases, and significantly so for inputs that trigger worst- case behaviour of the previous implementation. As an example, in my tests a 16K needle that matches the end of a 64K haystack is nearly 2000x faster with this implementation. Reviewed by: bapt (earlier), ed (earlier) Obtained from: musl (snapshot at commit c718f9fc) Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D2601
96 lines
2.7 KiB
Groff
96 lines
2.7 KiB
Groff
.\" Copyright (c) 2005 Pascal Gloor <pascal.gloor@spale.com>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote
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.\" products derived from this software without specific prior written
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.\" permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 17, 2017
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.Dt MEMMEM 3
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.Os
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.Sh NAME
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.Nm memmem
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.Nd "locate a byte substring in a byte string"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In string.h
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.Ft "void *"
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.Fo memmem
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.Fa "const void *big" "size_t big_len"
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.Fa "const void *little" "size_t little_len"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn memmem
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function
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locates the first occurrence of the byte string
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.Fa little
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in the byte string
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.Fa big .
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.Sh RETURN VALUES
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If
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.Fa little_len
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is zero
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.Fa big
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is returned (that is, an empty little is deemed to match at the beginning of
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big);
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if
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.Fa little
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occurs nowhere in
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.Fa big ,
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.Dv NULL
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is returned;
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otherwise a pointer to the first character of the first occurrence of
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.Fa little
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is returned.
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.Sh SEE ALSO
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.Xr memchr 3 ,
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.Xr strchr 3 ,
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.Xr strstr 3
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.Sh CONFORMING TO
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.Fn memmem
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is a GNU extension.
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.Sh HISTORY
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The
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.Fn memmem
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function first appeared in
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.Fx 6.0 .
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It was replaced with an optimized O(n) implementation from the musl libc
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project in
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.Fx 12.0 .
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.An Pascal Gloor Aq Mt pascal.gloor@spale.com
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provided this man page along with the previous implementation.
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.Sh BUGS
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This function was broken in Linux libc up to and including version 5.0.9
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and in GNU libc prior to version 2.1.
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Prior to
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.Fx 11.0
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.Nm
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returned
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.Dv NULL
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when
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.Fa little_len
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equals 0.
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