1 use crate::convert::{TryFrom, TryInto};
2 use crate::intrinsics::assert_unsafe_precondition;
3 use crate::num::NonZeroUsize;
4 use crate::{cmp, fmt, hash, mem, num};
6 /// A type storing a `usize` which is a power of two, and thus
7 /// represents a possible alignment in the rust abstract machine.
9 /// Note that particularly large alignments, while representable in this type,
10 /// are likely not to be supported by actual allocators and linkers.
11 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
12 #[derive(Copy, Clone, Eq)]
13 #[derive_const(PartialEq)]
15 pub struct Alignment(AlignmentEnum);
17 // Alignment is `repr(usize)`, but via extra steps.
18 const _: () = assert!(mem::size_of::<Alignment>() == mem::size_of::<usize>());
19 const _: () = assert!(mem::align_of::<Alignment>() == mem::align_of::<usize>());
21 fn _alignment_can_be_structurally_matched(a: Alignment) -> bool {
22 matches!(a, Alignment::MIN)
26 /// The smallest possible alignment, 1.
28 /// All addresses are always aligned at least this much.
33 /// #![feature(ptr_alignment_type)]
34 /// use std::ptr::Alignment;
36 /// assert_eq!(Alignment::MIN.as_usize(), 1);
38 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
39 pub const MIN: Self = Self(AlignmentEnum::_Align1Shl0);
41 /// Returns the alignment for a type.
43 /// This provides the same numerical value as [`mem::align_of`],
44 /// but in an `Alignment` instead of a `usize.
45 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
47 pub const fn of<T>() -> Self {
48 // SAFETY: rustc ensures that type alignment is always a power of two.
49 unsafe { Alignment::new_unchecked(mem::align_of::<T>()) }
52 /// Creates an `Alignment` from a `usize`, or returns `None` if it's
53 /// not a power of two.
55 /// Note that `0` is not a power of two, nor a valid alignment.
56 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
58 pub const fn new(align: usize) -> Option<Self> {
59 if align.is_power_of_two() {
60 // SAFETY: Just checked it only has one bit set
61 Some(unsafe { Self::new_unchecked(align) })
67 /// Creates an `Alignment` from a power-of-two `usize`.
71 /// `align` must be a power of two.
73 /// Equivalently, it must be `1 << exp` for some `exp` in `0..usize::BITS`.
74 /// It must *not* be zero.
75 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
76 #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
78 pub const unsafe fn new_unchecked(align: usize) -> Self {
79 // SAFETY: Precondition passed to the caller.
81 assert_unsafe_precondition!(
82 "Alignment::new_unchecked requires a power of two",
83 (align: usize) => align.is_power_of_two()
87 // SAFETY: By precondition, this must be a power of two, and
88 // our variants encompass all possible powers of two.
89 unsafe { mem::transmute::<usize, Alignment>(align) }
92 /// Returns the alignment as a [`usize`]
93 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
94 #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
96 pub const fn as_usize(self) -> usize {
100 /// Returns the alignment as a [`NonZeroUsize`]
101 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
103 pub const fn as_nonzero(self) -> NonZeroUsize {
104 // SAFETY: All the discriminants are non-zero.
105 unsafe { NonZeroUsize::new_unchecked(self.as_usize()) }
108 /// Returns the base-2 logarithm of the alignment.
110 /// This is always exact, as `self` represents a power of two.
115 /// #![feature(ptr_alignment_type)]
116 /// use std::ptr::Alignment;
118 /// assert_eq!(Alignment::of::<u8>().log2(), 0);
119 /// assert_eq!(Alignment::new(1024).unwrap().log2(), 10);
121 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
123 pub fn log2(self) -> u32 {
124 self.as_nonzero().trailing_zeros()
128 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
129 impl fmt::Debug for Alignment {
130 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
131 write!(f, "{:?} (1 << {:?})", self.as_nonzero(), self.log2())
135 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
136 impl TryFrom<NonZeroUsize> for Alignment {
137 type Error = num::TryFromIntError;
140 fn try_from(align: NonZeroUsize) -> Result<Alignment, Self::Error> {
141 align.get().try_into()
145 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
146 impl TryFrom<usize> for Alignment {
147 type Error = num::TryFromIntError;
150 fn try_from(align: usize) -> Result<Alignment, Self::Error> {
151 Self::new(align).ok_or(num::TryFromIntError(()))
155 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
156 impl From<Alignment> for NonZeroUsize {
158 fn from(align: Alignment) -> NonZeroUsize {
163 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
164 impl From<Alignment> for usize {
166 fn from(align: Alignment) -> usize {
171 #[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
172 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
173 impl const cmp::Ord for Alignment {
175 fn cmp(&self, other: &Self) -> cmp::Ordering {
176 self.as_nonzero().get().cmp(&other.as_nonzero().get())
180 #[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
181 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
182 impl const cmp::PartialOrd for Alignment {
184 fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
185 Some(self.cmp(other))
189 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
190 impl hash::Hash for Alignment {
192 fn hash<H: hash::Hasher>(&self, state: &mut H) {
193 self.as_nonzero().hash(state)
197 #[cfg(target_pointer_width = "16")]
198 type AlignmentEnum = AlignmentEnum16;
199 #[cfg(target_pointer_width = "32")]
200 type AlignmentEnum = AlignmentEnum32;
201 #[cfg(target_pointer_width = "64")]
202 type AlignmentEnum = AlignmentEnum64;
204 #[derive(Copy, Clone, Eq)]
205 #[derive_const(PartialEq)]
207 enum AlignmentEnum16 {
208 _Align1Shl0 = 1 << 0,
209 _Align1Shl1 = 1 << 1,
210 _Align1Shl2 = 1 << 2,
211 _Align1Shl3 = 1 << 3,
212 _Align1Shl4 = 1 << 4,
213 _Align1Shl5 = 1 << 5,
214 _Align1Shl6 = 1 << 6,
215 _Align1Shl7 = 1 << 7,
216 _Align1Shl8 = 1 << 8,
217 _Align1Shl9 = 1 << 9,
218 _Align1Shl10 = 1 << 10,
219 _Align1Shl11 = 1 << 11,
220 _Align1Shl12 = 1 << 12,
221 _Align1Shl13 = 1 << 13,
222 _Align1Shl14 = 1 << 14,
223 _Align1Shl15 = 1 << 15,
226 #[derive(Copy, Clone, Eq)]
227 #[derive_const(PartialEq)]
229 enum AlignmentEnum32 {
230 _Align1Shl0 = 1 << 0,
231 _Align1Shl1 = 1 << 1,
232 _Align1Shl2 = 1 << 2,
233 _Align1Shl3 = 1 << 3,
234 _Align1Shl4 = 1 << 4,
235 _Align1Shl5 = 1 << 5,
236 _Align1Shl6 = 1 << 6,
237 _Align1Shl7 = 1 << 7,
238 _Align1Shl8 = 1 << 8,
239 _Align1Shl9 = 1 << 9,
240 _Align1Shl10 = 1 << 10,
241 _Align1Shl11 = 1 << 11,
242 _Align1Shl12 = 1 << 12,
243 _Align1Shl13 = 1 << 13,
244 _Align1Shl14 = 1 << 14,
245 _Align1Shl15 = 1 << 15,
246 _Align1Shl16 = 1 << 16,
247 _Align1Shl17 = 1 << 17,
248 _Align1Shl18 = 1 << 18,
249 _Align1Shl19 = 1 << 19,
250 _Align1Shl20 = 1 << 20,
251 _Align1Shl21 = 1 << 21,
252 _Align1Shl22 = 1 << 22,
253 _Align1Shl23 = 1 << 23,
254 _Align1Shl24 = 1 << 24,
255 _Align1Shl25 = 1 << 25,
256 _Align1Shl26 = 1 << 26,
257 _Align1Shl27 = 1 << 27,
258 _Align1Shl28 = 1 << 28,
259 _Align1Shl29 = 1 << 29,
260 _Align1Shl30 = 1 << 30,
261 _Align1Shl31 = 1 << 31,
264 #[derive(Copy, Clone, Eq)]
265 #[derive_const(PartialEq)]
267 enum AlignmentEnum64 {
268 _Align1Shl0 = 1 << 0,
269 _Align1Shl1 = 1 << 1,
270 _Align1Shl2 = 1 << 2,
271 _Align1Shl3 = 1 << 3,
272 _Align1Shl4 = 1 << 4,
273 _Align1Shl5 = 1 << 5,
274 _Align1Shl6 = 1 << 6,
275 _Align1Shl7 = 1 << 7,
276 _Align1Shl8 = 1 << 8,
277 _Align1Shl9 = 1 << 9,
278 _Align1Shl10 = 1 << 10,
279 _Align1Shl11 = 1 << 11,
280 _Align1Shl12 = 1 << 12,
281 _Align1Shl13 = 1 << 13,
282 _Align1Shl14 = 1 << 14,
283 _Align1Shl15 = 1 << 15,
284 _Align1Shl16 = 1 << 16,
285 _Align1Shl17 = 1 << 17,
286 _Align1Shl18 = 1 << 18,
287 _Align1Shl19 = 1 << 19,
288 _Align1Shl20 = 1 << 20,
289 _Align1Shl21 = 1 << 21,
290 _Align1Shl22 = 1 << 22,
291 _Align1Shl23 = 1 << 23,
292 _Align1Shl24 = 1 << 24,
293 _Align1Shl25 = 1 << 25,
294 _Align1Shl26 = 1 << 26,
295 _Align1Shl27 = 1 << 27,
296 _Align1Shl28 = 1 << 28,
297 _Align1Shl29 = 1 << 29,
298 _Align1Shl30 = 1 << 30,
299 _Align1Shl31 = 1 << 31,
300 _Align1Shl32 = 1 << 32,
301 _Align1Shl33 = 1 << 33,
302 _Align1Shl34 = 1 << 34,
303 _Align1Shl35 = 1 << 35,
304 _Align1Shl36 = 1 << 36,
305 _Align1Shl37 = 1 << 37,
306 _Align1Shl38 = 1 << 38,
307 _Align1Shl39 = 1 << 39,
308 _Align1Shl40 = 1 << 40,
309 _Align1Shl41 = 1 << 41,
310 _Align1Shl42 = 1 << 42,
311 _Align1Shl43 = 1 << 43,
312 _Align1Shl44 = 1 << 44,
313 _Align1Shl45 = 1 << 45,
314 _Align1Shl46 = 1 << 46,
315 _Align1Shl47 = 1 << 47,
316 _Align1Shl48 = 1 << 48,
317 _Align1Shl49 = 1 << 49,
318 _Align1Shl50 = 1 << 50,
319 _Align1Shl51 = 1 << 51,
320 _Align1Shl52 = 1 << 52,
321 _Align1Shl53 = 1 << 53,
322 _Align1Shl54 = 1 << 54,
323 _Align1Shl55 = 1 << 55,
324 _Align1Shl56 = 1 << 56,
325 _Align1Shl57 = 1 << 57,
326 _Align1Shl58 = 1 << 58,
327 _Align1Shl59 = 1 << 59,
328 _Align1Shl60 = 1 << 60,
329 _Align1Shl61 = 1 << 61,
330 _Align1Shl62 = 1 << 62,
331 _Align1Shl63 = 1 << 63,