pub fn poly1305(key: &[u8; 32], msg: &[u8]) -> [u8; 16]Expand description
Poly1305 one-time authenticator: tag = ((Σ blockᵢ·r^(n−i)) mod (2¹³⁰−5)) + s mod 2¹²⁸. AVX2
(4 blocks/group via precomputed r¹..r⁴) for long messages, else scalar — bit-identical.