libfsm

libfsm compiles regular expressions to deterministic FSMs, ensuring supported patterns run in linear time without backtracking, as highlighted in the README for predictable performance in text processing.

lx is designed to be simple, expressive, and language-independent, focusing solely on efficient lexing without extra features, making it ideal for compiler front-end development.

Includes command-line tools like re(1) for regex matching and lx(1) for lexer generation, plus libraries (libfsm, libre) for FSM and regex compilation, as detailed in the features list.

Uses deterministic finite automata for pattern matching, avoiding the complexity and unpredictability of backtracking engines, which is core to its philosophy for performance-critical applications.