Add NonZero*::count_ones

Author: WaffleLapkin

library/core/src/num/nonzero.rs

@@ -1153,6 +1153,43 @@ macro_rules! nonzero_unsigned_signed_operations {
                     // so the result cannot be zero.
                     unsafe { $Ty::new_unchecked(self.get().saturating_pow(other)) }
                 }
+
+                /// Returns the number of ones in the binary representation of `self`.
+                ///
+                /// # Examples
+                ///
+                /// Basic usage:
+                ///
+                /// ```
+                /// #![feature(non_zero_count_ones)]
+                /// # fn main() { test().unwrap(); }
+                /// # fn test() -> Option<()> {
+                #[doc = concat!("# use std::num::{self, ", stringify!($Ty), "};")]
+                ///
+                /// let one = num::NonZeroU32::new(1)?;
+                /// let three = num::NonZeroU32::new(3)?;
+                #[doc = concat!("let a = ", stringify!($Ty), "::new(0b100_0000)?;")]
+                #[doc = concat!("let b = ", stringify!($Ty), "::new(0b100_0011)?;")]
+                ///
+                /// assert_eq!(a.count_ones(), one);
+                /// assert_eq!(b.count_ones(), three);
+                /// # Some(())
+                /// # }
+                /// ```
+                ///
+                #[unstable(feature = "non_zero_count_ones", issue = "none")]
+                #[rustc_const_unstable(feature = "non_zero_count_ones", issue = "none")]
+                #[doc(alias = "popcount")]
+                #[doc(alias = "popcnt")]
+                #[must_use = "this returns the result of the operation, \
+                            without modifying the original"]
+                #[inline(always)]
+                pub const fn count_ones(self) -> NonZeroU32 {
+                    // SAFETY:
+                    // `self` is non-zero, which means it has at least one bit set, which means
+                    // that the result is non-zero.
+                    unsafe { NonZeroU32::new_unchecked(self.get().count_ones()) }
+                }
             }
         )+
     }