BM(3)                     OpenBSD Programmer's Manual                    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(u_char *pattern, size_t patlen, u_char freq[256]);

     u_char *
     bm_exec(bm_pat *pdesc, u_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 giv-
     en 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, Software Practice and Experience, Fast String Searching,
     Volume 21, 11 (November 1991), 1221-48.

OpenBSD 2.6                      June 29, 1999                               1