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
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
use crate::convert::TryInto;
use crate::num::{NonZeroI128, NonZeroI16, NonZeroI32, NonZeroI64, NonZeroI8, NonZeroIsize};
use crate::num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize};

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[B; N]> for [A; N]
where
    A: PartialEq<B>,
{
    #[inline]
    fn eq(&self, other: &[B; N]) -> bool {
        SpecArrayEq::spec_eq(self, other)
    }
    #[inline]
    fn ne(&self, other: &[B; N]) -> bool {
        SpecArrayEq::spec_ne(self, other)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[B]> for [A; N]
where
    A: PartialEq<B>,
{
    #[inline]
    fn eq(&self, other: &[B]) -> bool {
        let b: Result<&[B; N], _> = other.try_into();
        match b {
            Ok(b) => *self == *b,
            Err(_) => false,
        }
    }
    #[inline]
    fn ne(&self, other: &[B]) -> bool {
        let b: Result<&[B; N], _> = other.try_into();
        match b {
            Ok(b) => *self != *b,
            Err(_) => true,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[A; N]> for [B]
where
    B: PartialEq<A>,
{
    #[inline]
    fn eq(&self, other: &[A; N]) -> bool {
        let b: Result<&[B; N], _> = self.try_into();
        match b {
            Ok(b) => *b == *other,
            Err(_) => false,
        }
    }
    #[inline]
    fn ne(&self, other: &[A; N]) -> bool {
        let b: Result<&[B; N], _> = self.try_into();
        match b {
            Ok(b) => *b != *other,
            Err(_) => true,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<&[B]> for [A; N]
where
    A: PartialEq<B>,
{
    #[inline]
    fn eq(&self, other: &&[B]) -> bool {
        *self == **other
    }
    #[inline]
    fn ne(&self, other: &&[B]) -> bool {
        *self != **other
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[A; N]> for &[B]
where
    B: PartialEq<A>,
{
    #[inline]
    fn eq(&self, other: &[A; N]) -> bool {
        **self == *other
    }
    #[inline]
    fn ne(&self, other: &[A; N]) -> bool {
        **self != *other
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<&mut [B]> for [A; N]
where
    A: PartialEq<B>,
{
    #[inline]
    fn eq(&self, other: &&mut [B]) -> bool {
        *self == **other
    }
    #[inline]
    fn ne(&self, other: &&mut [B]) -> bool {
        *self != **other
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B, const N: usize> PartialEq<[A; N]> for &mut [B]
where
    B: PartialEq<A>,
{
    #[inline]
    fn eq(&self, other: &[A; N]) -> bool {
        **self == *other
    }
    #[inline]
    fn ne(&self, other: &[A; N]) -> bool {
        **self != *other
    }
}

// NOTE: some less important impls are omitted to reduce code bloat
// __impl_slice_eq2! { [A; $N], &'b [B; $N] }
// __impl_slice_eq2! { [A; $N], &'b mut [B; $N] }

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Eq, const N: usize> Eq for [T; N] {}

trait SpecArrayEq<Other, const N: usize>: Sized {
    fn spec_eq(a: &[Self; N], b: &[Other; N]) -> bool;
    fn spec_ne(a: &[Self; N], b: &[Other; N]) -> bool;
}

impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
    default fn spec_eq(a: &[Self; N], b: &[Other; N]) -> bool {
        a[..] == b[..]
    }
    default fn spec_ne(a: &[Self; N], b: &[Other; N]) -> bool {
        a[..] != b[..]
    }
}

impl<T: IsRawEqComparable<U>, U, const N: usize> SpecArrayEq<U, N> for T {
    fn spec_eq(a: &[T; N], b: &[U; N]) -> bool {
        // SAFETY: This is why `IsRawEqComparable` is an `unsafe trait`.
        unsafe {
            let b = &*b.as_ptr().cast::<[T; N]>();
            crate::intrinsics::raw_eq(a, b)
        }
    }
    fn spec_ne(a: &[T; N], b: &[U; N]) -> bool {
        !Self::spec_eq(a, b)
    }
}

/// `U` exists on here mostly because `min_specialization` didn't let me
/// repeat the `T` type parameter in the above specialization, so instead
/// the `T == U` constraint comes from the impls on this.
/// # Safety
/// - Neither `Self` nor `U` has any padding.
/// - `Self` and `U` have the same layout.
/// - `Self: PartialEq<U>` is byte-wise (this means no floats, among other things)
#[rustc_specialization_trait]
unsafe trait IsRawEqComparable<U>: PartialEq<U> {}

macro_rules! is_raw_eq_comparable {
    ($($t:ty),+ $(,)?) => {$(
        unsafe impl IsRawEqComparable<$t> for $t {}
    )+};
}

// SAFETY: All the ordinary integer types have no padding, and are not pointers.
is_raw_eq_comparable!(u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize);

// SAFETY: bool and char have *niches*, but no *padding* (and these are not pointer types), so this
// is sound
is_raw_eq_comparable!(bool, char);

// SAFETY: Similarly, the non-zero types have a niche, but no undef and no pointers,
// and they compare like their underlying numeric type.
is_raw_eq_comparable!(
    NonZeroU8,
    NonZeroU16,
    NonZeroU32,
    NonZeroU64,
    NonZeroU128,
    NonZeroUsize,
    NonZeroI8,
    NonZeroI16,
    NonZeroI32,
    NonZeroI64,
    NonZeroI128,
    NonZeroIsize,
);

// SAFETY: The NonZero types have the "null" optimization guaranteed, and thus
// are also safe to equality-compare bitwise inside an `Option`.
// The way `PartialOrd` is defined for `Option` means that this wouldn't work
// for `<` or `>` on the signed types, but since we only do `==` it's fine.
is_raw_eq_comparable!(
    Option<NonZeroU8>,
    Option<NonZeroU16>,
    Option<NonZeroU32>,
    Option<NonZeroU64>,
    Option<NonZeroU128>,
    Option<NonZeroUsize>,
    Option<NonZeroI8>,
    Option<NonZeroI16>,
    Option<NonZeroI32>,
    Option<NonZeroI64>,
    Option<NonZeroI128>,
    Option<NonZeroIsize>,
);