pub fn fe25519_add(a: &[u64; 4], b: &[u64; 4]) -> [u64; 4]Expand description
a + b modulo 2^255 - 19 on 4 x 64-bit limbs, for inputs below 2^256 (result below 2^256, not fully reduced): a carry out of bit 256 is folded back as 38, twice. Constant time.