uuid.nx

uuid.nx -- UUID v4 (random) + v7 (time-ordered) generators. RFC 4122 (v4) + draft-ietf-uuidrev-rfc4122bis (v7). 16-byte identifier, formatted as 36-char hex string with hyphens. v4 = 122 random bits + 6 deterministic version/variant bits. Use when you don't need lexicographic time-ordering. v7 = 48-bit Unix ms timestamp prefix + 74 random bits + 6 version/variant bits. Sorts lexicographically by creation time, which is huge for database indexes -- rows cluster instead of scattering, and clustered B-trees stay warm. Use in preference to v4 for new systems. Invariants: U1 Every byte of the non-version/variant space is from /dev/urandom (via rand.nx). No PRNG state persists; each UUID is an independent sample. U2 Version + variant bits exactly match the RFC specs at byte positions 6 (version) and 8 (variant). U3 v7 timestamp is milliseconds since epoch, big-endian in bytes 0..5. Enables lexicographic time-ordering. U4 Formatting is deterministic: lowercase hex, no prefix, exact dash placement at 8-4-4-4-12 positions.