message: document IterUxDigits structs
diff: @@ -2288,11 +2288,18 @@ pub(crate) fn to_str_radix_reversed(u: &BigUint, radix: u32) -> Vec<u8> {
  res
  }
  -#[cfg(u64_digit)]
  +/// An iterator of `u32` digits representation of the `BigUint` ordered least
  +/// significant digit first.
  pub struct IterU32Digits<'a> {
  + #[cfg(u64_digit)]
  data: &'a [u64],
  + #[cfg(u64_digit)]
  next_is_lo: bool,
  + #[cfg(u64_digit)]
  last_hi_is_zero: bool,
  +
  + #[cfg(not(u64_digit))]
  + it: core::slice::Iter<'a, u32>,
  }
  #[cfg(u64_digit)]
  impl<'a> IterU32Digits<'a> {
  @@ -2361,10 +2368,6 @@ impl<'a> ExactSizeIterator for IterU32Digits<'a> {
  }
  }
  -#[cfg(not(u64_digit))]
  -pub struct IterU32Digits<'a> {
  - it: core::slice::Iter<'a, u32>,
  -}
  #[cfg(not(u64_digit))]
  impl<'a> IterU32Digits<'a> {
  fn new(data: &'a [u32]) -> Self {
  @@ -2403,9 +2406,14 @@ impl<'a> ExactSizeIterator for IterU32Digits<'a> {
  impl<'a> FusedIterator for IterU32Digits<'a> {}
  -#[cfg(not(u64_digit))]
  +/// An iterator of `u64` digits representation of the `BigUint` ordered least
  +/// significant digit first.
  pub struct IterU64Digits<'a> {
  + #[cfg(not(u64_digit))]
  it: core::slice::Chunks<'a, u32>,
  +
  + #[cfg(u64_digit)]
  + it: core::slice::Iter<'a, u64>,
  }
  #[cfg(not(u64_digit))]
  impl<'a> IterU64Digits<'a> {
  @@ -2441,10 +2449,6 @@ impl<'a> ExactSizeIterator for IterU64Digits<'a> {
  }
  }
  -#[cfg(u64_digit)]
  -pub struct IterU64Digits<'a> {
  - it: core::slice::Iter<'a, u64>,
  -}
  #[cfg(u64_digit)]
  impl<'a> IterU64Digits<'a> {
  fn new(data: &'a [u64]) -> Self {
  