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
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
#![no_std]
#![warn(missing_docs)]
#![allow(clippy::match_like_matches_macro)]
#![cfg_attr(feature = "nightly_portable_simd", feature(portable_simd))]

//! This crate gives small utilities for casting between plain data types.
//!
//! ## Basics
//!
//! Data comes in five basic forms in Rust, so we have five basic casting
//! functions:
//!
//! * `T` uses [`cast`]
//! * `&T` uses [`cast_ref`]
//! * `&mut T` uses [`cast_mut`]
//! * `&[T]` uses [`cast_slice`]
//! * `&mut [T]` uses [`cast_slice_mut`]
//!
//! Some casts will never fail (eg: `cast::<u32, f32>` always works), other
//! casts might fail (eg: `cast_ref::<[u8; 4], u32>` will fail if the reference
//! isn't already aligned to 4). Each casting function has a "try" version which
//! will return a `Result`, and the "normal" version which will simply panic on
//! invalid input.
//!
//! ## Using Your Own Types
//!
//! All the functions here are guarded by the [`Pod`] trait, which is a
//! sub-trait of the [`Zeroable`] trait.
//!
//! If you're very sure that your type is eligible, you can implement those
//! traits for your type and then they'll have full casting support. However,
//! these traits are `unsafe`, and you should carefully read the requirements
//! before adding the them to your own types.
//!
//! ## Features
//!
//! * This crate is core only by default, but if you're using Rust 1.36 or later
//!   you can enable the `extern_crate_alloc` cargo feature for some additional
//!   methods related to `Box` and `Vec`. Note that the `docs.rs` documentation
//!   is always built with `extern_crate_alloc` cargo feature enabled.

#[cfg(all(target_arch = "aarch64", feature = "aarch64_simd"))]
use core::arch::aarch64;
#[cfg(all(target_arch = "wasm32", feature = "wasm_simd"))]
use core::arch::wasm32;
#[cfg(target_arch = "x86")]
use core::arch::x86;
#[cfg(target_arch = "x86_64")]
use core::arch::x86_64;
//
use core::{marker::*, mem::*, num::*, ptr::*};

// Used from macros to ensure we aren't using some locally defined name and
// actually are referencing libcore. This also would allow pre-2018 edition
// crates to use our macros, but I'm not sure how important that is.
#[doc(hidden)]
pub use ::core as __core;

#[cfg(not(feature = "min_const_generics"))]
macro_rules! impl_unsafe_marker_for_array {
  ( $marker:ident , $( $n:expr ),* ) => {
    $(unsafe impl<T> $marker for [T; $n] where T: $marker {})*
  }
}

/// A macro to transmute between two types without requiring knowing size
/// statically.
macro_rules! transmute {
  ($val:expr) => {
    ::core::mem::transmute_copy(&::core::mem::ManuallyDrop::new($val))
  };
}

#[cfg(feature = "extern_crate_std")]
extern crate std;

#[cfg(feature = "extern_crate_alloc")]
extern crate alloc;
#[cfg(feature = "extern_crate_alloc")]
pub mod allocation;
#[cfg(feature = "extern_crate_alloc")]
pub use allocation::*;

mod anybitpattern;
pub use anybitpattern::*;

pub mod checked;
pub use checked::CheckedBitPattern;

mod internal;

mod zeroable;
pub use zeroable::*;
mod zeroable_in_option;
pub use zeroable_in_option::*;

mod pod;
pub use pod::*;
mod pod_in_option;
pub use pod_in_option::*;

mod no_uninit;
pub use no_uninit::*;

mod contiguous;
pub use contiguous::*;

mod offset_of;
pub use offset_of::*;

mod transparent;
pub use transparent::*;

#[cfg(feature = "derive")]
pub use bytemuck_derive::{
  AnyBitPattern, CheckedBitPattern, Contiguous, NoUninit, Pod,
  TransparentWrapper, Zeroable,
};

/// The things that can go wrong when casting between [`Pod`] data forms.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum PodCastError {
  /// You tried to cast a slice to an element type with a higher alignment
  /// requirement but the slice wasn't aligned.
  TargetAlignmentGreaterAndInputNotAligned,
  /// If the element size changes then the output slice changes length
  /// accordingly. If the output slice wouldn't be a whole number of elements
  /// then the conversion fails.
  OutputSliceWouldHaveSlop,
  /// When casting a slice you can't convert between ZST elements and non-ZST
  /// elements. When casting an individual `T`, `&T`, or `&mut T` value the
  /// source size and destination size must be an exact match.
  SizeMismatch,
  /// For this type of cast the alignments must be exactly the same and they
  /// were not so now you're sad.
  ///
  /// This error is generated **only** by operations that cast allocated types
  /// (such as `Box` and `Vec`), because in that case the alignment must stay
  /// exact.
  AlignmentMismatch,
}
#[cfg(not(target_arch = "spirv"))]
impl core::fmt::Display for PodCastError {
  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
    write!(f, "{:?}", self)
  }
}
#[cfg(feature = "extern_crate_std")]
impl std::error::Error for PodCastError {}

/// Re-interprets `&T` as `&[u8]`.
///
/// Any ZST becomes an empty slice, and in that case the pointer value of that
/// empty slice might not match the pointer value of the input reference.
#[inline]
pub fn bytes_of<T: NoUninit>(t: &T) -> &[u8] {
  unsafe { internal::bytes_of(t) }
}

/// Re-interprets `&mut T` as `&mut [u8]`.
///
/// Any ZST becomes an empty slice, and in that case the pointer value of that
/// empty slice might not match the pointer value of the input reference.
#[inline]
pub fn bytes_of_mut<T: NoUninit + AnyBitPattern>(t: &mut T) -> &mut [u8] {
  unsafe { internal::bytes_of_mut(t) }
}

/// Re-interprets `&[u8]` as `&T`.
///
/// ## Panics
///
/// This is [`try_from_bytes`] but will panic on error.
#[inline]
pub fn from_bytes<T: AnyBitPattern>(s: &[u8]) -> &T {
  unsafe { internal::from_bytes(s) }
}

/// Re-interprets `&mut [u8]` as `&mut T`.
///
/// ## Panics
///
/// This is [`try_from_bytes_mut`] but will panic on error.
#[inline]
pub fn from_bytes_mut<T: NoUninit + AnyBitPattern>(s: &mut [u8]) -> &mut T {
  unsafe { internal::from_bytes_mut(s) }
}

/// Reads from the bytes as if they were a `T`.
///
/// ## Failure
/// * If the `bytes` length is not equal to `size_of::<T>()`.
#[inline]
pub fn try_pod_read_unaligned<T: AnyBitPattern>(
  bytes: &[u8],
) -> Result<T, PodCastError> {
  unsafe { internal::try_pod_read_unaligned(bytes) }
}

/// Reads the slice into a `T` value.
///
/// ## Panics
/// * This is like `try_pod_read_unaligned` but will panic on failure.
#[inline]
pub fn pod_read_unaligned<T: AnyBitPattern>(bytes: &[u8]) -> T {
  unsafe { internal::pod_read_unaligned(bytes) }
}

/// Re-interprets `&[u8]` as `&T`.
///
/// ## Failure
///
/// * If the slice isn't aligned for the new type
/// * If the slice's length isn’t exactly the size of the new type
#[inline]
pub fn try_from_bytes<T: AnyBitPattern>(s: &[u8]) -> Result<&T, PodCastError> {
  unsafe { internal::try_from_bytes(s) }
}

/// Re-interprets `&mut [u8]` as `&mut T`.
///
/// ## Failure
///
/// * If the slice isn't aligned for the new type
/// * If the slice's length isn’t exactly the size of the new type
#[inline]
pub fn try_from_bytes_mut<T: NoUninit + AnyBitPattern>(
  s: &mut [u8],
) -> Result<&mut T, PodCastError> {
  unsafe { internal::try_from_bytes_mut(s) }
}

/// Cast `T` into `U`
///
/// ## Panics
///
/// * This is like [`try_cast`](try_cast), but will panic on a size mismatch.
#[inline]
pub fn cast<A: NoUninit, B: AnyBitPattern>(a: A) -> B {
  unsafe { internal::cast(a) }
}

/// Cast `&mut T` into `&mut U`.
///
/// ## Panics
///
/// This is [`try_cast_mut`] but will panic on error.
#[inline]
pub fn cast_mut<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(
  a: &mut A,
) -> &mut B {
  unsafe { internal::cast_mut(a) }
}

/// Cast `&T` into `&U`.
///
/// ## Panics
///
/// This is [`try_cast_ref`] but will panic on error.
#[inline]
pub fn cast_ref<A: NoUninit, B: AnyBitPattern>(a: &A) -> &B {
  unsafe { internal::cast_ref(a) }
}

/// Cast `&[A]` into `&[B]`.
///
/// ## Panics
///
/// This is [`try_cast_slice`] but will panic on error.
#[inline]
pub fn cast_slice<A: NoUninit, B: AnyBitPattern>(a: &[A]) -> &[B] {
  unsafe { internal::cast_slice(a) }
}

/// Cast `&mut [T]` into `&mut [U]`.
///
/// ## Panics
///
/// This is [`try_cast_slice_mut`] but will panic on error.
#[inline]
pub fn cast_slice_mut<
  A: NoUninit + AnyBitPattern,
  B: NoUninit + AnyBitPattern,
>(
  a: &mut [A],
) -> &mut [B] {
  unsafe { internal::cast_slice_mut(a) }
}

/// As `align_to`, but safe because of the [`Pod`] bound.
#[inline]
pub fn pod_align_to<T: NoUninit, U: AnyBitPattern>(
  vals: &[T],
) -> (&[T], &[U], &[T]) {
  unsafe { vals.align_to::<U>() }
}

/// As `align_to_mut`, but safe because of the [`Pod`] bound.
#[inline]
pub fn pod_align_to_mut<
  T: NoUninit + AnyBitPattern,
  U: NoUninit + AnyBitPattern,
>(
  vals: &mut [T],
) -> (&mut [T], &mut [U], &mut [T]) {
  unsafe { vals.align_to_mut::<U>() }
}

/// Try to cast `T` into `U`.
///
/// Note that for this particular type of cast, alignment isn't a factor. The
/// input value is semantically copied into the function and then returned to a
/// new memory location which will have whatever the required alignment of the
/// output type is.
///
/// ## Failure
///
/// * If the types don't have the same size this fails.
#[inline]
pub fn try_cast<A: NoUninit, B: AnyBitPattern>(
  a: A,
) -> Result<B, PodCastError> {
  unsafe { internal::try_cast(a) }
}

/// Try to convert a `&T` into `&U`.
///
/// ## Failure
///
/// * If the reference isn't aligned in the new type
/// * If the source type and target type aren't the same size.
#[inline]
pub fn try_cast_ref<A: NoUninit, B: AnyBitPattern>(
  a: &A,
) -> Result<&B, PodCastError> {
  unsafe { internal::try_cast_ref(a) }
}

/// Try to convert a `&mut T` into `&mut U`.
///
/// As [`try_cast_ref`], but `mut`.
#[inline]
pub fn try_cast_mut<
  A: NoUninit + AnyBitPattern,
  B: NoUninit + AnyBitPattern,
>(
  a: &mut A,
) -> Result<&mut B, PodCastError> {
  unsafe { internal::try_cast_mut(a) }
}

/// Try to convert `&[A]` into `&[B]` (possibly with a change in length).
///
/// * `input.as_ptr() as usize == output.as_ptr() as usize`
/// * `input.len() * size_of::<A>() == output.len() * size_of::<B>()`
///
/// ## Failure
///
/// * If the target type has a greater alignment requirement and the input slice
///   isn't aligned.
/// * If the target element type is a different size from the current element
///   type, and the output slice wouldn't be a whole number of elements when
///   accounting for the size change (eg: 3 `u16` values is 1.5 `u32` values, so
///   that's a failure).
/// * Similarly, you can't convert between a [ZST](https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts)
///   and a non-ZST.
#[inline]
pub fn try_cast_slice<A: NoUninit, B: AnyBitPattern>(
  a: &[A],
) -> Result<&[B], PodCastError> {
  unsafe { internal::try_cast_slice(a) }
}

/// Try to convert `&mut [A]` into `&mut [B]` (possibly with a change in
/// length).
///
/// As [`try_cast_slice`], but `&mut`.
#[inline]
pub fn try_cast_slice_mut<
  A: NoUninit + AnyBitPattern,
  B: NoUninit + AnyBitPattern,
>(
  a: &mut [A],
) -> Result<&mut [B], PodCastError> {
  unsafe { internal::try_cast_slice_mut(a) }
}