Function fiat_crypto::curve25519_64::fiat_25519_carry

pub fn fiat_25519_carry(
    out1: &mut fiat_25519_tight_field_element,
    arg1: &fiat_25519_loose_field_element
)

The function fiat_25519_carry reduces a field element.

Postconditions: eval out1 mod m = eval arg1 mod m