Implement div_ceil for NonZero<unsigned>

[tyilo]

ACP: rust-lang/libs-team#471

[rustbot]

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[joboet]

Could you inline div_ceil here? That will lead to unchecked operations being used for the division and remainder which might allow some more optimizations.

[tyilo]

Do you mean something like the following?

pub const fn div_ceil(self, rhs: Self) -> Self {
  let a = self.get();
  let b = rhs.get();
  let d = a / b;
  let r = a % b;
  let v = if r > 0 {
    d + 1
  } else {
    d
  };
  // SAFETY: ceiled division of two positive integers can never be zero.
  unsafe { Self::new_unchecked(v) }
}

Why would this allow more optimizations? They seem to produce the same ASM: https://play.rust-lang.org/?version=stable&mode=release&edition=2021&gist=735568e0474e49fa0a1b86d773a486d0