hex.nx

hex.nx -- lowercase hex encoder + decoder. Complement to base64.nx for the common "print bytes as text" use cases where readability matters more than density: - SHA-256 / SHA-3 digest display - Git-style object IDs - TLS handshake transcripts for debugging - URL query parameters carrying short binary values Deterministic output (lowercase always). Decoder tolerates both upper and lower case. No "0x" prefix, no whitespace. Invariants: H1 Encoder output is exactly 2*n chars for n input bytes. H2 Decoder requires even-length input; rejects odd-length with a negative return. H3 Decoder rejects any non-hex char (not [0-9A-Fa-f]) with a negative return -- no silent skip. H4 Round-trip is exact: decode(encode(x)) == x for any byte sequence.