1. A method for classification, comprising: extracting, in a decision logic pipeline, respective classification keys from a collection of data items, each classification key comprising a string of bits; receiving a corpus of rules for matching to the classification keys, each rule comprising a respective set of unmasked bits having corresponding bit values, and at least some of the rules comprising masked bits in addition to the unmasked bits; extracting rule patterns from the corpus, each rule pattern defining a different, respective sequence of masked and unmasked bits to which one or more of the rules conform; grouping the rule patterns into extended rule patterns, such that the respective set of unmasked bits in any rule pattern that is grouped into any given extended rule pattern is a superset of the unmasked bits in the given extended rule pattern, whereby the rule patterns that are grouped into at least one of the extended rule patterns include at least first and second rule patterns having different, respective numbers of unmasked bits; computing rule entries corresponding to the rules using the extended rule patterns into which the rule patterns are grouped, and storing the rule entries in a random access memory (RAM); and classifying the data items by matching the respective classification keys to the rule entries in the RAM.