.\" Copyright (c) 1994
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Andrew Hume of AT&T Bell Laboratories.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\"	$OpenBSD: bm.3,v 1.11 2013/06/05 03:39:23 tedu Exp $
.\"
.Dd $Mdocdate: June 5 2013 $
.Dt BM 3
.Os
.Sh NAME
.Nm bm_comp ,
.Nm bm_exec ,
.Nm bm_free
.Nd Boyer-Moore string search
.Sh SYNOPSIS
.In sys/types.h
.In bm.h
.Ft bm_pat *
.Fn bm_comp "const unsigned char *pattern" "size_t patlen" \
    "const unsigned char freq[256]"
.Ft unsigned char *
.Fn bm_exec "bm_pat *pdesc" "unsigned char *text" "size_t len"
.Ft void
.Fn bm_free "bm_pat *pdesc"
.Sh DESCRIPTION
These routines implement an efficient mechanism to find an
occurrence of a byte string within another byte string.
.Pp
.Fn bm_comp
evaluates
.Fa patlen
bytes starting at
.Fa pattern
and returns a pointer to a structure describing them.
The bytes referenced by
.Fa pattern
may be of any value.
.Pp
The search takes advantage of the frequency distribution of the
bytes in the text to be searched.
If specified,
.Ar freq
should be an array of 256 values,
with higher values indicating that the corresponding character occurs
more frequently.
(A less than optimal frequency distribution can only result in less
than optimal performance, not incorrect results.)
If
.Ar freq
is
.Dv NULL ,
a system default table is used.
.Pp
.Fn bm_exec
returns a pointer to the leftmost occurrence of the string given to
.Fn bm_comp
within
.Ar text ,
or
.Dv NULL
if none occurs.
The number of bytes in
.Ar text
must be specified by
.Ar len .
.Pp
Space allocated for the returned description is discarded
by calling
.Fn bm_free
with the returned description as an argument.
.Pp
The asymptotic speed of
.Fn bm_exec
is
.Pf O Ns Pq len / patlen .
.Sh SEE ALSO
.Xr regexp 3 ,
.Xr strstr 3
.Rs
.%R "Fast String Searching"
.%A Andrew Hume
.%A Daniel Sunday
.%J "Software Practice and Experience"
.%V Volume 21, 11 (November 1991)
.%P 1221-48
.Re
.Sh HISTORY
The
.Fn bm_comp ,
.Fn bm_exec ,
and
.Fn bm_free
functions first appeared in
.Nx 1.0 .