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Implement div_ceil for NonZero<unsigned> #132665

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Implement div_ceil for NonZero<unsigned> #132665

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29 changes: 29 additions & 0 deletions library/core/src/num/nonzero.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1214,6 +1214,35 @@ macro_rules! nonzero_integer_signedness_dependent_impls {
*self = *self % other;
}
}

impl NonZero<$Int> {
/// Calculates the quotient of `self` and `rhs`, rounding the result towards positive infinity.
///
/// The result is guaranteed to be non-zero.
///
/// # Examples
///
/// ```
/// # #![feature(unsigned_nonzero_div_ceil)]
/// # use std::num::NonZero;
#[doc = concat!("let one = NonZero::new(1", stringify!($Int), ").unwrap();")]
#[doc = concat!("let max = NonZero::new(", stringify!($Int), "::MAX).unwrap();")]
/// assert_eq!(one.div_ceil(max), one);
///
#[doc = concat!("let two = NonZero::new(2", stringify!($Int), ").unwrap();")]
#[doc = concat!("let three = NonZero::new(3", stringify!($Int), ").unwrap();")]
/// assert_eq!(three.div_ceil(two), two);
/// ```
#[unstable(feature = "unsigned_nonzero_div_ceil", issue = "none")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn div_ceil(self, rhs: Self) -> Self {
let v = self.get().div_ceil(rhs.get());
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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.

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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

// SAFETY: ceiled division of two positive integers can never be zero.
unsafe { Self::new_unchecked(v) }
}
}
};
// Impls for signed nonzero types only.
(signed $Int:ty) => {
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