An apparatus comprises pattern matching circuitry for detecting instances of at least one predetermined pattern of symbols within a subject stream of symbols. Encoding circuitry is provided for generating an encoded stream of symbols from an input stream of symbols, where the encoding circuitry maps a number of consecutive repetitions of a same pattern of one or more symbols detected within the input stream to a single instance of a symbol of the encoded stream and a corresponding repetition indicator indicative of the number of consecutive repetitions. Control circuitry controls the pattern matching circuitry to process the encoded stream of symbols generated by the encoding circuitry as the subject stream.