116 lines
3.7 KiB
Groff
116 lines
3.7 KiB
Groff
.\" $NetBSD: bm.3,v 1.5 2002/02/07 07:00:31 ross Exp $
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.\"
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.\" Copyright (c) 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Andrew Hume of AT&T Bell Laboratories.
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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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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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.\" from: @(#)bm.3 8.4 (Berkeley) 6/21/94
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.\"
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.Dd April 8, 2001
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.Dt BM 3
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.Os
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.Sh NAME
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.Nm bm_comp ,
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.Nm bm_exec ,
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.Nm bm_free
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.Nd Boyer-Moore string search
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include \*[Lt]sys/types.h\*[Gt]
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.Fd #include \*[Lt]bm.h\*[Gt]
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.Ft bm_pat *
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.Fn bm_comp "u_char *pattern" "size_t patlen" "u_char freq[256]"
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.Ft u_char *
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.Fn bm_exec "bm_pat *pdesc" "u_char *text" "size_t len"
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.Ft void
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.Fn bm_free "bm_pat *pdesc"
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.Sh DESCRIPTION
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These routines implement an efficient mechanism to find an
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occurrence of a byte string within another byte string.
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.Pp
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.Fn bm_comp
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evaluates the
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.Fa patlen
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bytes starting at
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.Fa pattern ,
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and returns a pointer to a structure describing them.
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The bytes referenced by
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.Fa pattern
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may be of any value.
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.Pp
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The search takes advantage of the frequency distribution of the
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bytes in the text to be searched.
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If specified,
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.Fa freq
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should be an array of 256 values,
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with higher values indicating that the corresponding character occurs
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more frequently.
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(A less than optimal frequency distribution can only result in less
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than optimal performance, not incorrect results.)
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If
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.Fa freq
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is NULL,
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a system default table is used.
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.Pp
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.Fn bm_exec
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returns a pointer to the leftmost occurrence of the string given to
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.Fn bm_comp
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within
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.Fa text ,
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or NULL if none occurs.
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The number of bytes in
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.Fa text
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must be specified by
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.Fa len .
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.Pp
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Space allocated for the returned description is discarded
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by calling
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.Fn bm_free
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with the returned description as an argument.
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.Pp
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The asymptotic speed of
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.Fn bm_exec
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is O(len/patlen).
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.Sh SEE ALSO
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.Xr regexp 3 ,
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.Xr strstr 3
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.Rs
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.%A Hume and Sunday
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.%D November 1991
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.%J "Software Practice and Experience"
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.%P pp. 1221-48
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.%T "Fast String Searching"
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.%V Vol. 21, 11
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.Re
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