blob: 2f520e0878c8bfbfecb647141aa4b95abf39a82f [file] [log] [blame]
use std::ops::{Add, Mul};
use std::num::Wrapping;
/// Defines an additive identity element for `Self`.
pub trait Zero: Sized + Add<Self, Output = Self> {
/// Returns the additive identity element of `Self`, `0`.
///
/// # Laws
///
/// ```{.text}
/// a + 0 = a ∀ a ∈ Self
/// 0 + a = a ∀ a ∈ Self
/// ```
///
/// # 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.
// FIXME (#5527): This should be an associated constant
fn zero() -> Self;
/// Returns `true` if `self` is equal to the additive identity.
#[inline]
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 == $v }
}
}
}
zero_impl!(usize, 0usize);
zero_impl!(u8, 0u8);
zero_impl!(u16, 0u16);
zero_impl!(u32, 0u32);
zero_impl!(u64, 0u64);
zero_impl!(isize, 0isize);
zero_impl!(i8, 0i8);
zero_impl!(i16, 0i16);
zero_impl!(i32, 0i32);
zero_impl!(i64, 0i64);
zero_impl!(f32, 0.0f32);
zero_impl!(f64, 0.0f64);
impl<T: Zero> Zero for Wrapping<T> where Wrapping<T>: Add<Output=Wrapping<T>> {
fn is_zero(&self) -> bool {
self.0.is_zero()
}
fn zero() -> Self {
Wrapping(T::zero())
}
}
/// Defines a multiplicative identity element for `Self`.
pub trait One: Sized + Mul<Self, Output = Self> {
/// Returns the multiplicative identity element of `Self`, `1`.
///
/// # Laws
///
/// ```{.text}
/// a * 1 = a ∀ a ∈ Self
/// 1 * a = a ∀ a ∈ Self
/// ```
///
/// # Purity
///
/// This function should return the same result at all times regardless of
/// external mutable state, for example values stored in TLS or in
/// `static mut`s.
// FIXME (#5527): This should be an associated constant
fn one() -> Self;
}
macro_rules! one_impl {
($t:ty, $v:expr) => {
impl One for $t {
#[inline]
fn one() -> $t { $v }
}
}
}
one_impl!(usize, 1usize);
one_impl!(u8, 1u8);
one_impl!(u16, 1u16);
one_impl!(u32, 1u32);
one_impl!(u64, 1u64);
one_impl!(isize, 1isize);
one_impl!(i8, 1i8);
one_impl!(i16, 1i16);
one_impl!(i32, 1i32);
one_impl!(i64, 1i64);
one_impl!(f32, 1.0f32);
one_impl!(f64, 1.0f64);
impl<T: One> One for Wrapping<T> where Wrapping<T>: Mul<Output=Wrapping<T>> {
fn one() -> Self {
Wrapping(T::one())
}
}
// Some helper functions provided for backwards compatibility.
/// Returns the additive identity, `0`.
#[inline(always)] pub fn zero<T: Zero>() -> T { Zero::zero() }
/// Returns the multiplicative identity, `1`.
#[inline(always)] pub fn one<T: One>() -> T { One::one() }
macro_rules! test_wrapping_identities {
($($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]
fn wrapping_identities() {
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));
}