Function exp_u64
pub(in ::fmt::num::imp) fn exp_u64(f: &mut Formatter<'_>, n: u64, is_nonnegative: bool, letter_e: u8) -> Resultexp_u64pub(in ::fmt::num::imp) fn exp_u64(f: &mut Formatter<'_>, n: u64, is_nonnegative: bool, letter_e: u8) -> Result