Performance

REAL is the linear-time, ReDoS-safe engine that is also fast: ahead of std::regex everywhere and of RE2 on most general shapes, trading blows with PCRE2-JIT and Rust’s regex crate, and orders of magnitude ahead of every backtracker on adversarial (ReDoS) inputs — safety it never trades for the speed.

How it compares

	REAL	std::regex	RE2	Rust regex	PCRE2-JIT	Python re
Linear-time, ReDoS-safe	yes	no	yes	yes	no	no
Lookarounds	yes	yes	no	no	yes	yes
Possessive / atomic	yes¹	no	no	no	yes	yes
Header-only, zero-dep	yes	yes²	no	no	no	—
Constexpr match	yes	no	no	no	no	no
Drop-in Python re	yes³	no	no	no	no	yes

¹ Tier 1 (linear time): a single atom, or one wrapped in one capturing group — [^x]*+, \d++, (?>\w+). A compound body is rejected, never silently mis-matched. ² Part of the C++ standard library. ³ For the supported subset (no backreferences).

Every production engine that ships lookarounds backtracks. Every linear-time engine drops them. REAL is the only one with both.

ReDoS

On the classic catastrophic pattern, backtrackers explode or refuse at a few dozen characters. REAL and RE2 stay linear at a hundred thousand. Two honest legs: the required-literal prefilter on (a+)+b, and the bare VM on (a+)+ with nothing to short-circuit. The measured table is §C of the ledger.

The ledger

Tables, machines and the version stamp live in BENCHMARKS.md on GitHub — not on this site. Per-train notes live in CHANGELOG.md. A re-stamp must not silently rewrite a published page.

What a timing claim is allowed to say: MEASUREMENT.md.

Reproduce with make bench-engines (C++) and make python-bench (binding vs re). Both check match-count equality before timing — a fast wrong answer is not a win.