Abstract: A method and apparatus are disclosed for determining the lengths of one or more substrings of an input string that matches a regular expression (regex) The input string is searched for the regex using an non-deterministic finite automaton (NFA), and upon detecting a match state a selected portion of the input string is marked as a match string. The NFA is inverted to create a reverse NFA that embodies the inverse of the regex. For some embodiments, the reverse NFA is created by inverting the NFA such that the match state of the NFA becomes the initial state of the reverse NFA, the initial state of the NFA becomes the match state of the reverse NFA, and the goto transitions of the NFA are inverted to form corresponding goto transitions in the reverse NFA. The match string is reversed and searched for the inverted regex using the reverse NFA, and a counter is incremented for each character processed during the reverse search operation.

Abstract: A counter circuit is configured to simultaneously maintain individual character match count values for a plurality of overlapping substrings of an input string of characters that match a portion of a regular expression stored in a plurality of rows of content addressable memory (CAM) cells of a ternary CAM device. The counter circuit is selectable between a normal operational mode in which all matching portions of the input string are identified, and a minimum match length operational mode in which only matching portions of the input string that have at least a specified minimum number of characters are identified.