bytemuck/
pod.rs

1use super::*;
2
3/// Marker trait for "plain old data".
4///
5/// The point of this trait is that once something is marked "plain old data"
6/// you can really go to town with the bit fiddling and bit casting. Therefore,
7/// it's a relatively strong claim to make about a type. Do not add this to your
8/// type casually.
9///
10/// **Reminder:** The results of casting around bytes between data types are
11/// _endian dependant_. Little-endian machines are the most common, but
12/// big-endian machines do exist (and big-endian is also used for "network
13/// order" bytes).
14///
15/// ## Safety
16///
17/// * The type must be inhabited (eg: no
18///   [Infallible](core::convert::Infallible)).
19/// * The type must allow any bit pattern (eg: no `bool` or `char`, which have
20///   illegal bit patterns).
21/// * The type must not contain any uninit (or padding) bytes, either in the
22///   middle or on the end (eg: no `#[repr(C)] struct Foo(u8, u16)`, which has
23///   padding in the middle, and also no `#[repr(C)] struct Foo(u16, u8)`, which
24///   has padding on the end).
25/// * The type needs to have all fields also be `Pod`.
26/// * The type needs to be `repr(C)` or `repr(transparent)`. In the case of
27///   `repr(C)`, the `packed` and `align` repr modifiers can be used as long as
28///   all other rules end up being followed.
29/// * It is disallowed for types to contain pointer types, `Cell`, `UnsafeCell`,
30///   atomics, and any other forms of interior mutability.
31/// * More precisely: A shared reference to the type must allow reads, and
32///   *only* reads. RustBelt's separation logic is based on the notion that a
33///   type is allowed to define a sharing predicate, its own invariant that must
34///   hold for shared references, and this predicate is the reasoning that allow
35///   it to deal with atomic and cells etc. We require the sharing predicate to
36///   be trivial and permit only read-only access.
37pub unsafe trait Pod: Zeroable + Copy + 'static {}
38
39unsafe impl Pod for () {}
40unsafe impl Pod for u8 {}
41unsafe impl Pod for i8 {}
42unsafe impl Pod for u16 {}
43unsafe impl Pod for i16 {}
44unsafe impl Pod for u32 {}
45unsafe impl Pod for i32 {}
46unsafe impl Pod for u64 {}
47unsafe impl Pod for i64 {}
48unsafe impl Pod for usize {}
49unsafe impl Pod for isize {}
50unsafe impl Pod for u128 {}
51unsafe impl Pod for i128 {}
52#[cfg(feature = "nightly_float")]
53unsafe impl Pod for f16 {}
54unsafe impl Pod for f32 {}
55unsafe impl Pod for f64 {}
56#[cfg(feature = "nightly_float")]
57unsafe impl Pod for f128 {}
58unsafe impl<T: Pod> Pod for Wrapping<T> {}
59
60#[cfg(feature = "pod_saturating")]
61unsafe impl<T: Pod> Pod for core::num::Saturating<T>{}
62
63#[cfg(feature = "unsound_ptr_pod_impl")]
64#[cfg_attr(
65  feature = "nightly_docs",
66  doc(cfg(feature = "unsound_ptr_pod_impl"))
67)]
68unsafe impl<T: 'static> Pod for *mut T {}
69#[cfg(feature = "unsound_ptr_pod_impl")]
70#[cfg_attr(
71  feature = "nightly_docs",
72  doc(cfg(feature = "unsound_ptr_pod_impl"))
73)]
74unsafe impl<T: 'static> Pod for *const T {}
75#[cfg(feature = "unsound_ptr_pod_impl")]
76#[cfg_attr(
77  feature = "nightly_docs",
78  doc(cfg(feature = "unsound_ptr_pod_impl"))
79)]
80unsafe impl<T: 'static> PodInOption for NonNull<T> {}
81
82unsafe impl<T: ?Sized + 'static> Pod for PhantomData<T> {}
83unsafe impl Pod for PhantomPinned {}
84unsafe impl<T: Pod> Pod for core::mem::ManuallyDrop<T> {}
85
86// Note(Lokathor): MaybeUninit can NEVER be Pod.
87
88#[cfg(feature = "min_const_generics")]
89#[cfg_attr(feature = "nightly_docs", doc(cfg(feature = "min_const_generics")))]
90unsafe impl<T, const N: usize> Pod for [T; N] where T: Pod {}
91
92#[cfg(not(feature = "min_const_generics"))]
93impl_unsafe_marker_for_array!(
94  Pod, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
95  20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 48, 64, 96, 128, 256,
96  512, 1024, 2048, 4096
97);
98
99impl_unsafe_marker_for_simd!(
100  #[cfg(all(target_arch = "wasm32", feature = "wasm_simd"))]
101  unsafe impl Pod for wasm32::{v128}
102);
103
104impl_unsafe_marker_for_simd!(
105  #[cfg(all(target_arch = "aarch64", feature = "aarch64_simd"))]
106  unsafe impl Pod for aarch64::{
107    float32x2_t, float32x2x2_t, float32x2x3_t, float32x2x4_t, float32x4_t,
108    float32x4x2_t, float32x4x3_t, float32x4x4_t, float64x1_t, float64x1x2_t,
109    float64x1x3_t, float64x1x4_t, float64x2_t, float64x2x2_t, float64x2x3_t,
110    float64x2x4_t, int16x4_t, int16x4x2_t, int16x4x3_t, int16x4x4_t, int16x8_t,
111    int16x8x2_t, int16x8x3_t, int16x8x4_t, int32x2_t, int32x2x2_t, int32x2x3_t,
112    int32x2x4_t, int32x4_t, int32x4x2_t, int32x4x3_t, int32x4x4_t, int64x1_t,
113    int64x1x2_t, int64x1x3_t, int64x1x4_t, int64x2_t, int64x2x2_t, int64x2x3_t,
114    int64x2x4_t, int8x16_t, int8x16x2_t, int8x16x3_t, int8x16x4_t, int8x8_t,
115    int8x8x2_t, int8x8x3_t, int8x8x4_t, poly16x4_t, poly16x4x2_t, poly16x4x3_t,
116    poly16x4x4_t, poly16x8_t, poly16x8x2_t, poly16x8x3_t, poly16x8x4_t,
117    poly64x1_t, poly64x1x2_t, poly64x1x3_t, poly64x1x4_t, poly64x2_t,
118    poly64x2x2_t, poly64x2x3_t, poly64x2x4_t, poly8x16_t, poly8x16x2_t,
119    poly8x16x3_t, poly8x16x4_t, poly8x8_t, poly8x8x2_t, poly8x8x3_t, poly8x8x4_t,
120    uint16x4_t, uint16x4x2_t, uint16x4x3_t, uint16x4x4_t, uint16x8_t,
121    uint16x8x2_t, uint16x8x3_t, uint16x8x4_t, uint32x2_t, uint32x2x2_t,
122    uint32x2x3_t, uint32x2x4_t, uint32x4_t, uint32x4x2_t, uint32x4x3_t,
123    uint32x4x4_t, uint64x1_t, uint64x1x2_t, uint64x1x3_t, uint64x1x4_t,
124    uint64x2_t, uint64x2x2_t, uint64x2x3_t, uint64x2x4_t, uint8x16_t,
125    uint8x16x2_t, uint8x16x3_t, uint8x16x4_t, uint8x8_t, uint8x8x2_t,
126    uint8x8x3_t, uint8x8x4_t,
127  }
128);
129
130impl_unsafe_marker_for_simd!(
131  #[cfg(target_arch = "x86")]
132  unsafe impl Pod for x86::{
133    __m128i, __m128, __m128d,
134    __m256i, __m256, __m256d,
135  }
136);
137
138impl_unsafe_marker_for_simd!(
139  #[cfg(target_arch = "x86_64")]
140  unsafe impl Pod for x86_64::{
141    __m128i, __m128, __m128d,
142    __m256i, __m256, __m256d,
143  }
144);
145
146#[rustversion::before(2026-01-27)] // See https://github.com/Lokathor/bytemuck/issues/343
147#[cfg(feature = "nightly_portable_simd")]
148#[cfg_attr(
149  feature = "nightly_docs",
150  doc(cfg(feature = "nightly_portable_simd"))
151)]
152unsafe impl<T, const N: usize> Pod for core::simd::Simd<T, N>
153where
154  T: core::simd::SimdElement + Pod,
155  core::simd::LaneCount<N>: core::simd::SupportedLaneCount,
156{
157}
158
159#[rustversion::since(2026-01-27)] // See https://github.com/Lokathor/bytemuck/issues/343
160#[cfg(feature = "nightly_portable_simd")]
161#[cfg_attr(
162  feature = "nightly_docs",
163  doc(cfg(feature = "nightly_portable_simd"))
164)]
165unsafe impl<T, const N: usize> Pod for core::simd::Simd<T, N>
166where
167  T: core::simd::SimdElement + Pod,
168{
169}
170
171impl_unsafe_marker_for_simd!(
172  #[cfg(all(target_arch = "x86", feature = "avx512_simd"))]
173  unsafe impl Pod for x86::{
174    __m512, __m512d, __m512i
175  }
176);
177
178impl_unsafe_marker_for_simd!(
179  #[cfg(all(target_arch = "x86_64", feature = "avx512_simd"))]
180  unsafe impl Pod for x86_64::{
181    __m512, __m512d, __m512i
182  }
183);
184
185impl_unsafe_marker_for_simd!(
186    #[cfg(all(target_arch = "x86", feature = "avx512_simd"))]
187  unsafe impl Pod for x86::{
188    __m128bh, __m256bh, __m512bh
189  }
190);
191
192impl_unsafe_marker_for_simd!(
193    #[cfg(all(target_arch = "x86_64", feature = "avx512_simd"))]
194  unsafe impl Pod for x86_64::{
195    __m128bh, __m256bh, __m512bh
196  }
197);
bytemuck/pod.rs

bytemuck/
pod.rs
