bm_comp, bm_exec, bm_free - Boyer-Moore string search
Standard C Library (libc, -lc)
bm_comp(u_char *pattern, size_t patlen, u_char freq);
bm_exec(bm_pat *pdesc, u_char *text, size_t len);
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).
Hume and Sunday, "Fast String Searching", Software Practice and
Experience, Vol. 21, 11, pp. 1221-48, November 1991.
BSD April 8, 2001 BSD
[ Back ]