1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
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() }


#[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));
}