NAME
bm_comp,
bm_exec,
bm_free
—
Boyer-Moore string search
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <bm.h>
bm_pat *
bm_comp(
unsigned
char *pattern,
size_t
patlen,
unsigned char
freq[256]);
unsigned char *
bm_exec(
bm_pat
*pdesc,
unsigned char
*text,
size_t len);
void
bm_free(
bm_pat
*pdesc);
DESCRIPTION
These routines implement an efficient mechanism to find an occurrence of a byte
string within another byte string.
bm_comp() evaluates the
patlen bytes
starting at
pattern, and returns a pointer to a
structure describing them. The bytes referenced by
pattern may be of any value.
The search takes advantage of the frequency distribution of the bytes in the
text to be searched. If specified,
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
freq is
NULL
, a system default
table is used.
bm_exec() returns a pointer to the leftmost occurrence of the
string given to
bm_comp() within
text,
or
NULL
if none occurs. The number of bytes in
text must be specified by
len.
Space allocated for the returned description is discarded by calling
bm_free() with the returned description as an argument.
The asymptotic speed of
bm_exec() is O(len/patlen).
SEE ALSO
regexp(3),
strstr(3)
Hume and Sunday,
Fast String Searching, Software
Practice and Experience, Vol. 21, 11,
pp. 1221-48, November
1991.