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).