1 files changed, 206 insertions, 0 deletions
diff --git a/third_party/rust/num-traits/src/identities.rs b/third_party/rust/num-traits/src/identities.rs
new file mode 100644
index 0000000000..7a99566d9e
--- /dev/null
+++ b/third_party/rust/num-traits/src/identities.rs
@@ -0,0 +1,206 @@
+use core::num::Wrapping;
+use core::ops::{Add, Mul};
+
+/// Defines an additive identity element for `Self`.
+///
+/// # Laws
+///
+/// ```{.text}
+/// a + 0 = a       ∀ a ∈ Self
+/// 0 + a = a       ∀ a ∈ Self
+/// ```
+pub trait Zero: Sized + Add<Self, Output = Self> {
+    /// Returns the additive identity element of `Self`, `0`.
+    /// # Purity
+    ///
+    /// This function should return the same result at all times regardless of
+    /// external mutable state, for example values stored in TLS or in
+    /// `static mut`s.
+    // This cannot be an associated constant, because of bignums.
+    fn zero() -> Self;
+
+    /// Sets `self` to the additive identity element of `Self`, `0`.
+    fn set_zero(&mut self) {
+        *self = Zero::zero();
+    }
+
+    /// Returns `true` if `self` is equal to the additive identity.
+    fn is_zero(&self) -> bool;
+}
+
+macro_rules! zero_impl {
+    ($t:ty, $v:expr) => {
+        impl Zero for $t {
+            #[inline]
+            fn zero() -> $t {
+                $v
+            }
+            #[inline]
+            fn is_zero(&self) -> bool {
+                *self == $v
+            }
+        }
+    };
+}
+
+zero_impl!(usize, 0);
+zero_impl!(u8, 0);
+zero_impl!(u16, 0);
+zero_impl!(u32, 0);
+zero_impl!(u64, 0);
+#[cfg(has_i128)]
+zero_impl!(u128, 0);
+
+zero_impl!(isize, 0);
+zero_impl!(i8, 0);
+zero_impl!(i16, 0);
+zero_impl!(i32, 0);
+zero_impl!(i64, 0);
+#[cfg(has_i128)]
+zero_impl!(i128, 0);
+
+zero_impl!(f32, 0.0);
+zero_impl!(f64, 0.0);
+
+impl<T: Zero> Zero for Wrapping<T>
+where
+    Wrapping<T>: Add<Output = Wrapping<T>>,
+{
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+
+    fn set_zero(&mut self) {
+        self.0.set_zero();
+    }
+
+    fn zero() -> Self {
+        Wrapping(T::zero())
+    }
+}
+
+/// Defines a multiplicative identity element for `Self`.
+///
+/// # Laws
+///
+/// ```{.text}
+/// a * 1 = a       ∀ a ∈ Self
+/// 1 * a = a       ∀ a ∈ Self
+/// ```
+pub trait One: Sized + Mul<Self, Output = Self> {
+    /// Returns the multiplicative identity element of `Self`, `1`.
+    ///
+    /// # Purity
+    ///
+    /// This function should return the same result at all times regardless of
+    /// external mutable state, for example values stored in TLS or in
+    /// `static mut`s.
+    // This cannot be an associated constant, because of bignums.
+    fn one() -> Self;
+
+    /// Sets `self` to the multiplicative identity element of `Self`, `1`.
+    fn set_one(&mut self) {
+        *self = One::one();
+    }
+
+    /// Returns `true` if `self` is equal to the multiplicative identity.
+    ///
+    /// For performance reasons, it's best to implement this manually.
+    /// After a semver bump, this method will be required, and the
+    /// `where Self: PartialEq` bound will be removed.
+    #[inline]
+    fn is_one(&self) -> bool
+    where
+        Self: PartialEq,
+    {
+        *self == Self::one()
+    }
+}
+
+macro_rules! one_impl {
+    ($t:ty, $v:expr) => {
+        impl One for $t {
+            #[inline]
+            fn one() -> $t {
+                $v
+            }
+            #[inline]
+            fn is_one(&self) -> bool {
+                *self == $v
+            }
+        }
+    };
+}
+
+one_impl!(usize, 1);
+one_impl!(u8, 1);
+one_impl!(u16, 1);
+one_impl!(u32, 1);
+one_impl!(u64, 1);
+#[cfg(has_i128)]
+one_impl!(u128, 1);
+
+one_impl!(isize, 1);
+one_impl!(i8, 1);
+one_impl!(i16, 1);
+one_impl!(i32, 1);
+one_impl!(i64, 1);
+#[cfg(has_i128)]
+one_impl!(i128, 1);
+
+one_impl!(f32, 1.0);
+one_impl!(f64, 1.0);
+
+impl<T: One> One for Wrapping<T>
+where
+    Wrapping<T>: Mul<Output = Wrapping<T>>,
+{
+    fn set_one(&mut self) {
+        self.0.set_one();
+    }
+
+    fn one() -> Self {
+        Wrapping(T::one())
+    }
+}
+
+// Some helper functions provided for backwards compatibility.
+
+/// Returns the additive identity, `0`.
+#[inline(always)]
+pub fn zero<T: Zero>() -> T {
+    Zero::zero()
+}
+
+/// Returns the multiplicative identity, `1`.
+#[inline(always)]
+pub fn one<T: One>() -> T {
+    One::one()
+}
+
+#[test]
+fn wrapping_identities() {
+    macro_rules! test_wrapping_identities {
+        ($($t:ty)+) => {
+            $(
+                assert_eq!(zero::<$t>(), zero::<Wrapping<$t>>().0);
+                assert_eq!(one::<$t>(), one::<Wrapping<$t>>().0);
+                assert_eq!((0 as $t).is_zero(), Wrapping(0 as $t).is_zero());
+                assert_eq!((1 as $t).is_zero(), Wrapping(1 as $t).is_zero());
+            )+
+        };
+    }
+
+    test_wrapping_identities!(isize i8 i16 i32 i64 usize u8 u16 u32 u64);
+}
+
+#[test]
+fn wrapping_is_zero() {
+    fn require_zero<T: Zero>(_: &T) {}
+    require_zero(&Wrapping(42));
+}
+#[test]
+fn wrapping_is_one() {
+    fn require_one<T: One>(_: &T) {}
+    require_one(&Wrapping(42));
+}