BM(3)

NAME
bm_comp, bm_exec, bm_free - Boyer-Moore string search

SYNOPSIS
#include <sys/types.h>
#include <bm.h>
bm_pat *
bm_comp(const unsigned char *pattern, size_t patlen, const 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 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) Fast String Searching, Andrew Hume, Daniel Sunday, Software Practice and Experience, Volume 21, 11 (November 1991), 1221-48.

HISTORY
The bm_comp(), bm_exec(), and bm_free() functions first appeared in NetBSD 1.0.