BM(3) BSD Library Functions Manual BM(3)
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 struc-
ture 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 indicat-
ing 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