149 lines
3.6 KiB
Rust
149 lines
3.6 KiB
Rust
use std::ops::{Add, Mul};
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use std::num::Wrapping;
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/// Defines an additive identity element for `Self`.
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pub trait Zero: Sized + Add<Self, Output = Self> {
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/// Returns the additive identity element of `Self`, `0`.
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///
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/// # Laws
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///
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/// ```{.text}
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/// a + 0 = a ∀ a ∈ Self
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/// 0 + a = a ∀ a ∈ Self
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/// ```
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///
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/// # Purity
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///
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/// This function should return the same result at all times regardless of
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/// external mutable state, for example values stored in TLS or in
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/// `static mut`s.
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// FIXME (#5527): This should be an associated constant
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fn zero() -> Self;
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/// Returns `true` if `self` is equal to the additive identity.
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#[inline]
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fn is_zero(&self) -> bool;
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}
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macro_rules! zero_impl {
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($t:ty, $v:expr) => {
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impl Zero for $t {
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#[inline]
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fn zero() -> $t { $v }
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#[inline]
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fn is_zero(&self) -> bool { *self == $v }
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}
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}
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}
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zero_impl!(usize, 0usize);
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zero_impl!(u8, 0u8);
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zero_impl!(u16, 0u16);
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zero_impl!(u32, 0u32);
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zero_impl!(u64, 0u64);
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zero_impl!(isize, 0isize);
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zero_impl!(i8, 0i8);
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zero_impl!(i16, 0i16);
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zero_impl!(i32, 0i32);
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zero_impl!(i64, 0i64);
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zero_impl!(f32, 0.0f32);
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zero_impl!(f64, 0.0f64);
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impl<T: Zero> Zero for Wrapping<T> where Wrapping<T>: Add<Output=Wrapping<T>> {
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fn is_zero(&self) -> bool {
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self.0.is_zero()
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}
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fn zero() -> Self {
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Wrapping(T::zero())
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}
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}
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/// Defines a multiplicative identity element for `Self`.
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pub trait One: Sized + Mul<Self, Output = Self> {
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/// Returns the multiplicative identity element of `Self`, `1`.
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///
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/// # Laws
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///
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/// ```{.text}
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/// a * 1 = a ∀ a ∈ Self
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/// 1 * a = a ∀ a ∈ Self
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/// ```
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///
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/// # Purity
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///
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/// This function should return the same result at all times regardless of
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/// external mutable state, for example values stored in TLS or in
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/// `static mut`s.
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// FIXME (#5527): This should be an associated constant
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fn one() -> Self;
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}
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macro_rules! one_impl {
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($t:ty, $v:expr) => {
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impl One for $t {
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#[inline]
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fn one() -> $t { $v }
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}
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}
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}
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one_impl!(usize, 1usize);
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one_impl!(u8, 1u8);
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one_impl!(u16, 1u16);
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one_impl!(u32, 1u32);
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one_impl!(u64, 1u64);
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one_impl!(isize, 1isize);
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one_impl!(i8, 1i8);
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one_impl!(i16, 1i16);
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one_impl!(i32, 1i32);
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one_impl!(i64, 1i64);
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one_impl!(f32, 1.0f32);
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one_impl!(f64, 1.0f64);
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impl<T: One> One for Wrapping<T> where Wrapping<T>: Mul<Output=Wrapping<T>> {
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fn one() -> Self {
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Wrapping(T::one())
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}
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}
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// Some helper functions provided for backwards compatibility.
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/// Returns the additive identity, `0`.
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#[inline(always)] pub fn zero<T: Zero>() -> T { Zero::zero() }
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/// Returns the multiplicative identity, `1`.
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#[inline(always)] pub fn one<T: One>() -> T { One::one() }
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#[test]
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fn wrapping_identities() {
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macro_rules! test_wrapping_identities {
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($($t:ty)+) => {
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$(
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assert_eq!(zero::<$t>(), zero::<Wrapping<$t>>().0);
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assert_eq!(one::<$t>(), one::<Wrapping<$t>>().0);
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assert_eq!((0 as $t).is_zero(), Wrapping(0 as $t).is_zero());
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assert_eq!((1 as $t).is_zero(), Wrapping(1 as $t).is_zero());
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)+
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};
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}
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test_wrapping_identities!(isize i8 i16 i32 i64 usize u8 u16 u32 u64);
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}
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#[test]
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fn wrapping_is_zero() {
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fn require_zero<T: Zero>(_: &T) {}
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require_zero(&Wrapping(42));
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}
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#[test]
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fn wrapping_is_one() {
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fn require_one<T: One>(_: &T) {}
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require_one(&Wrapping(42));
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}
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