294 lines
7.2 KiB
Rust
294 lines
7.2 KiB
Rust
use core::num::Wrapping;
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use core::ops::{Add, Mul};
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/// Defines an additive identity element for `Self`.
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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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pub trait Zero: Sized + Add<Self, Output = Self> {
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/// Returns the additive identity element of `Self`, `0`.
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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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// This cannot be an associated constant, because of bignums.
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fn zero() -> Self;
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/// Sets `self` to the additive identity element of `Self`, `0`.
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fn set_zero(&mut self) {
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*self = Zero::zero();
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}
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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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/// Supplimentary trait for [`Zero`](trait.Zero.html) types which can be
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/// expressed as compile-time constants.
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///
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/// This is implemented for all primitive types, and should be implemented
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/// wherever possible. Implementors must ensure that `ConstZero::ZERO` is
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/// the same value produced by [`Zero::zero()`](trait.Zero.html#tymethod.zero).
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#[cfg(has_associated_consts)]
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pub trait ConstZero: Zero {
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/// Additive identity: see [`Zero::zero()`](trait.Zero.html#tymethod.zero).
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const ZERO: Self;
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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() -> $t {
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$v
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}
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#[inline]
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fn is_zero(&self) -> bool {
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*self == $v
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}
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}
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};
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}
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#[cfg(has_associated_consts)]
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macro_rules! zero_const_impl {
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($t:ty, $v:expr) => {
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zero_impl!($t, $v);
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impl ConstZero for $t {
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const ZERO: $t = $v;
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}
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};
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}
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#[cfg(not(has_associated_consts))]
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macro_rules! zero_const_impl {
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($t:ty, $v:expr) => { zero_impl!($t, $v); };
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}
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zero_const_impl!(usize, 0);
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zero_const_impl!(u8, 0);
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zero_const_impl!(u16, 0);
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zero_const_impl!(u32, 0);
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zero_const_impl!(u64, 0);
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#[cfg(has_i128)]
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zero_const_impl!(u128, 0);
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zero_const_impl!(isize, 0);
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zero_const_impl!(i8, 0);
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zero_const_impl!(i16, 0);
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zero_const_impl!(i32, 0);
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zero_const_impl!(i64, 0);
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#[cfg(has_i128)]
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zero_const_impl!(i128, 0);
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zero_const_impl!(f32, 0.0);
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zero_const_impl!(f64, 0.0);
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impl<T: Zero> Zero for Wrapping<T>
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where
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Wrapping<T>: Add<Output = Wrapping<T>>,
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{
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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 set_zero(&mut self) {
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self.0.set_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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#[cfg(has_associated_consts)]
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impl<T: ConstZero> ConstZero for Wrapping<T>
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where
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Wrapping<T>: Zero,
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{
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const ZERO: Self = Wrapping(T::ZERO);
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}
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/// Defines a multiplicative identity element for `Self`.
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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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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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/// # 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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// This cannot be an associated constant, because of bignums.
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fn one() -> Self;
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/// Sets `self` to the multiplicative identity element of `Self`, `1`.
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fn set_one(&mut self) {
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*self = One::one();
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}
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/// Returns `true` if `self` is equal to the multiplicative identity.
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///
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/// For performance reasons, it's best to implement this manually.
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/// After a semver bump, this method will be required, and the
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/// `where Self: PartialEq` bound will be removed.
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#[inline]
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fn is_one(&self) -> bool
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where
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Self: PartialEq,
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{
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*self == Self::one()
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}
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}
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/// Supplimentary trait for [`One`](trait.One.html) types which can be
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/// expressed as compile-time constants.
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///
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/// This is implemented for all primitive types, and should be implemented
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/// wherever possible. Implementors must ensure that `ConstOne::ONE` is
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/// the same value produced by [`One::one()`](trait.One.html#tymethod.one).
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#[cfg(has_associated_consts)]
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pub trait ConstOne: One {
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/// Multiplicative identity: see [`One::one`](trait.One.html#tymethod.one).
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const 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() -> $t {
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$v
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}
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#[inline]
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fn is_one(&self) -> bool {
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*self == $v
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}
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}
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};
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}
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#[cfg(has_associated_consts)]
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macro_rules! one_const_impl {
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($t:ty, $v:expr) => {
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one_impl!($t, $v);
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impl ConstOne for $t {
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const ONE: $t = $v;
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}
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};
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}
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#[cfg(not(has_associated_consts))]
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macro_rules! one_const_impl {
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($t:ty, $v:expr) => { one_impl!($t, $v); };
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}
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one_const_impl!(usize, 1);
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one_const_impl!(u8, 1);
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one_const_impl!(u16, 1);
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one_const_impl!(u32, 1);
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one_const_impl!(u64, 1);
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#[cfg(has_i128)]
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one_const_impl!(u128, 1);
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one_const_impl!(isize, 1);
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one_const_impl!(i8, 1);
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one_const_impl!(i16, 1);
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one_const_impl!(i32, 1);
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one_const_impl!(i64, 1);
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#[cfg(has_i128)]
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one_const_impl!(i128, 1);
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one_const_impl!(f32, 1.0);
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one_const_impl!(f64, 1.0);
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impl<T: One> One for Wrapping<T>
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where
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Wrapping<T>: Mul<Output = Wrapping<T>>,
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{
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fn set_one(&mut self) {
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self.0.set_one();
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}
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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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#[cfg(has_associated_consts)]
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impl<T: ConstOne> ConstOne for Wrapping<T>
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where
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Wrapping<T>: One,
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{
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const ONE: Self = Wrapping(T::ONE);
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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)]
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pub fn zero<T: Zero>() -> T {
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Zero::zero()
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}
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/// Returns the multiplicative identity, `1`.
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#[inline(always)]
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pub fn one<T: One>() -> T {
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One::one()
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}
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#[test]
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#[cfg(has_associated_consts)]
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fn const_identies() {
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macro_rules! test_zero_one {
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($zero:expr, $one:expr; $($t:ty),+) => {
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$(
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assert_eq!(<$t as ConstZero>::ZERO, $zero);
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assert_eq!(<$t as ConstZero>::ZERO, <$t as Zero>::zero());
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assert_eq!(<$t as ConstOne>::ONE, $one);
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assert_eq!(<$t as ConstOne>::ONE, <$t as One>::one());
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)+
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}
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}
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test_zero_one!(0, 1; isize, i8, i16, i32, i64, usize, u8, u16, u32, u64);
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test_zero_one!(0.0, 1.0; f32, f64);
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}
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#[test]
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fn wrapping_identities() {
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macro_rules! test_wrapping_identities {
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($($t:ty)+) => {
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$(
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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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