NAME
bm_comp, bm_exec,
bm_free —
Boyer-Moore string search
LIBRARY
library “libc”
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
Hume and Sunday, Fast String Searching, Software Practice and Experience, Vol. 21, 11, pp. 1221-48, November 1991.