core/ptr/
alignment.rs

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
use crate::num::NonZero;
use crate::ub_checks::assert_unsafe_precondition;
use crate::{cmp, fmt, hash, mem, num};

/// A type storing a `usize` which is a power of two, and thus
/// represents a possible alignment in the Rust abstract machine.
///
/// Note that particularly large alignments, while representable in this type,
/// are likely not to be supported by actual allocators and linkers.
#[unstable(feature = "ptr_alignment_type", issue = "102070")]
#[derive(Copy, Clone, PartialEq, Eq)]
#[repr(transparent)]
pub struct Alignment(AlignmentEnum);

// Alignment is `repr(usize)`, but via extra steps.
const _: () = assert!(mem::size_of::<Alignment>() == mem::size_of::<usize>());
const _: () = assert!(mem::align_of::<Alignment>() == mem::align_of::<usize>());

fn _alignment_can_be_structurally_matched(a: Alignment) -> bool {
    matches!(a, Alignment::MIN)
}

impl Alignment {
    /// The smallest possible alignment, 1.
    ///
    /// All addresses are always aligned at least this much.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ptr_alignment_type)]
    /// use std::ptr::Alignment;
    ///
    /// assert_eq!(Alignment::MIN.as_usize(), 1);
    /// ```
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    pub const MIN: Self = Self(AlignmentEnum::_Align1Shl0);

    /// Returns the alignment for a type.
    ///
    /// This provides the same numerical value as [`mem::align_of`],
    /// but in an `Alignment` instead of a `usize`.
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const fn of<T>() -> Self {
        // SAFETY: rustc ensures that type alignment is always a power of two.
        unsafe { Alignment::new_unchecked(mem::align_of::<T>()) }
    }

    /// Creates an `Alignment` from a `usize`, or returns `None` if it's
    /// not a power of two.
    ///
    /// Note that `0` is not a power of two, nor a valid alignment.
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const fn new(align: usize) -> Option<Self> {
        if align.is_power_of_two() {
            // SAFETY: Just checked it only has one bit set
            Some(unsafe { Self::new_unchecked(align) })
        } else {
            None
        }
    }

    /// Creates an `Alignment` from a power-of-two `usize`.
    ///
    /// # Safety
    ///
    /// `align` must be a power of two.
    ///
    /// Equivalently, it must be `1 << exp` for some `exp` in `0..usize::BITS`.
    /// It must *not* be zero.
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const unsafe fn new_unchecked(align: usize) -> Self {
        assert_unsafe_precondition!(
            check_language_ub,
            "Alignment::new_unchecked requires a power of two",
            (align: usize = align) => align.is_power_of_two()
        );

        // SAFETY: By precondition, this must be a power of two, and
        // our variants encompass all possible powers of two.
        unsafe { mem::transmute::<usize, Alignment>(align) }
    }

    /// Returns the alignment as a [`usize`].
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const fn as_usize(self) -> usize {
        self.0 as usize
    }

    /// Returns the alignment as a <code>[NonZero]<[usize]></code>.
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const fn as_nonzero(self) -> NonZero<usize> {
        // SAFETY: All the discriminants are non-zero.
        unsafe { NonZero::new_unchecked(self.as_usize()) }
    }

    /// Returns the base-2 logarithm of the alignment.
    ///
    /// This is always exact, as `self` represents a power of two.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ptr_alignment_type)]
    /// use std::ptr::Alignment;
    ///
    /// assert_eq!(Alignment::of::<u8>().log2(), 0);
    /// assert_eq!(Alignment::new(1024).unwrap().log2(), 10);
    /// ```
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const fn log2(self) -> u32 {
        self.as_nonzero().trailing_zeros()
    }

    /// Returns a bit mask that can be used to match this alignment.
    ///
    /// This is equivalent to `!(self.as_usize() - 1)`.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ptr_alignment_type)]
    /// #![feature(ptr_mask)]
    /// use std::ptr::{Alignment, NonNull};
    ///
    /// #[repr(align(1))] struct Align1(u8);
    /// #[repr(align(2))] struct Align2(u16);
    /// #[repr(align(4))] struct Align4(u32);
    /// let one = <NonNull<Align1>>::dangling().as_ptr();
    /// let two = <NonNull<Align2>>::dangling().as_ptr();
    /// let four = <NonNull<Align4>>::dangling().as_ptr();
    ///
    /// assert_eq!(four.mask(Alignment::of::<Align1>().mask()), four);
    /// assert_eq!(four.mask(Alignment::of::<Align2>().mask()), four);
    /// assert_eq!(four.mask(Alignment::of::<Align4>().mask()), four);
    /// assert_ne!(one.mask(Alignment::of::<Align4>().mask()), one);
    /// ```
    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
    #[inline]
    pub const fn mask(self) -> usize {
        // SAFETY: The alignment is always nonzero, and therefore decrementing won't overflow.
        !(unsafe { self.as_usize().unchecked_sub(1) })
    }
}

#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl fmt::Debug for Alignment {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:?} (1 << {:?})", self.as_nonzero(), self.log2())
    }
}

#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl TryFrom<NonZero<usize>> for Alignment {
    type Error = num::TryFromIntError;

    #[inline]
    fn try_from(align: NonZero<usize>) -> Result<Alignment, Self::Error> {
        align.get().try_into()
    }
}

#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl TryFrom<usize> for Alignment {
    type Error = num::TryFromIntError;

    #[inline]
    fn try_from(align: usize) -> Result<Alignment, Self::Error> {
        Self::new(align).ok_or(num::TryFromIntError(()))
    }
}

#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl From<Alignment> for NonZero<usize> {
    #[inline]
    fn from(align: Alignment) -> NonZero<usize> {
        align.as_nonzero()
    }
}

#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl From<Alignment> for usize {
    #[inline]
    fn from(align: Alignment) -> usize {
        align.as_usize()
    }
}

#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl cmp::Ord for Alignment {
    #[inline]
    fn cmp(&self, other: &Self) -> cmp::Ordering {
        self.as_nonzero().get().cmp(&other.as_nonzero().get())
    }
}

#[rustc_const_unstable(feature = "const_alloc_layout", issue = "67521")]
#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl cmp::PartialOrd for Alignment {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
        Some(self.cmp(other))
    }
}

#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl hash::Hash for Alignment {
    #[inline]
    fn hash<H: hash::Hasher>(&self, state: &mut H) {
        self.as_nonzero().hash(state)
    }
}

/// Returns [`Alignment::MIN`], which is valid for any type.
#[unstable(feature = "ptr_alignment_type", issue = "102070")]
impl Default for Alignment {
    fn default() -> Alignment {
        Alignment::MIN
    }
}

#[cfg(target_pointer_width = "16")]
#[derive(Copy, Clone, PartialEq, Eq)]
#[repr(u16)]
enum AlignmentEnum {
    _Align1Shl0 = 1 << 0,
    _Align1Shl1 = 1 << 1,
    _Align1Shl2 = 1 << 2,
    _Align1Shl3 = 1 << 3,
    _Align1Shl4 = 1 << 4,
    _Align1Shl5 = 1 << 5,
    _Align1Shl6 = 1 << 6,
    _Align1Shl7 = 1 << 7,
    _Align1Shl8 = 1 << 8,
    _Align1Shl9 = 1 << 9,
    _Align1Shl10 = 1 << 10,
    _Align1Shl11 = 1 << 11,
    _Align1Shl12 = 1 << 12,
    _Align1Shl13 = 1 << 13,
    _Align1Shl14 = 1 << 14,
    _Align1Shl15 = 1 << 15,
}

#[cfg(target_pointer_width = "32")]
#[derive(Copy, Clone, PartialEq, Eq)]
#[repr(u32)]
enum AlignmentEnum {
    _Align1Shl0 = 1 << 0,
    _Align1Shl1 = 1 << 1,
    _Align1Shl2 = 1 << 2,
    _Align1Shl3 = 1 << 3,
    _Align1Shl4 = 1 << 4,
    _Align1Shl5 = 1 << 5,
    _Align1Shl6 = 1 << 6,
    _Align1Shl7 = 1 << 7,
    _Align1Shl8 = 1 << 8,
    _Align1Shl9 = 1 << 9,
    _Align1Shl10 = 1 << 10,
    _Align1Shl11 = 1 << 11,
    _Align1Shl12 = 1 << 12,
    _Align1Shl13 = 1 << 13,
    _Align1Shl14 = 1 << 14,
    _Align1Shl15 = 1 << 15,
    _Align1Shl16 = 1 << 16,
    _Align1Shl17 = 1 << 17,
    _Align1Shl18 = 1 << 18,
    _Align1Shl19 = 1 << 19,
    _Align1Shl20 = 1 << 20,
    _Align1Shl21 = 1 << 21,
    _Align1Shl22 = 1 << 22,
    _Align1Shl23 = 1 << 23,
    _Align1Shl24 = 1 << 24,
    _Align1Shl25 = 1 << 25,
    _Align1Shl26 = 1 << 26,
    _Align1Shl27 = 1 << 27,
    _Align1Shl28 = 1 << 28,
    _Align1Shl29 = 1 << 29,
    _Align1Shl30 = 1 << 30,
    _Align1Shl31 = 1 << 31,
}

#[cfg(target_pointer_width = "64")]
#[derive(Copy, Clone, PartialEq, Eq)]
#[repr(u64)]
enum AlignmentEnum {
    _Align1Shl0 = 1 << 0,
    _Align1Shl1 = 1 << 1,
    _Align1Shl2 = 1 << 2,
    _Align1Shl3 = 1 << 3,
    _Align1Shl4 = 1 << 4,
    _Align1Shl5 = 1 << 5,
    _Align1Shl6 = 1 << 6,
    _Align1Shl7 = 1 << 7,
    _Align1Shl8 = 1 << 8,
    _Align1Shl9 = 1 << 9,
    _Align1Shl10 = 1 << 10,
    _Align1Shl11 = 1 << 11,
    _Align1Shl12 = 1 << 12,
    _Align1Shl13 = 1 << 13,
    _Align1Shl14 = 1 << 14,
    _Align1Shl15 = 1 << 15,
    _Align1Shl16 = 1 << 16,
    _Align1Shl17 = 1 << 17,
    _Align1Shl18 = 1 << 18,
    _Align1Shl19 = 1 << 19,
    _Align1Shl20 = 1 << 20,
    _Align1Shl21 = 1 << 21,
    _Align1Shl22 = 1 << 22,
    _Align1Shl23 = 1 << 23,
    _Align1Shl24 = 1 << 24,
    _Align1Shl25 = 1 << 25,
    _Align1Shl26 = 1 << 26,
    _Align1Shl27 = 1 << 27,
    _Align1Shl28 = 1 << 28,
    _Align1Shl29 = 1 << 29,
    _Align1Shl30 = 1 << 30,
    _Align1Shl31 = 1 << 31,
    _Align1Shl32 = 1 << 32,
    _Align1Shl33 = 1 << 33,
    _Align1Shl34 = 1 << 34,
    _Align1Shl35 = 1 << 35,
    _Align1Shl36 = 1 << 36,
    _Align1Shl37 = 1 << 37,
    _Align1Shl38 = 1 << 38,
    _Align1Shl39 = 1 << 39,
    _Align1Shl40 = 1 << 40,
    _Align1Shl41 = 1 << 41,
    _Align1Shl42 = 1 << 42,
    _Align1Shl43 = 1 << 43,
    _Align1Shl44 = 1 << 44,
    _Align1Shl45 = 1 << 45,
    _Align1Shl46 = 1 << 46,
    _Align1Shl47 = 1 << 47,
    _Align1Shl48 = 1 << 48,
    _Align1Shl49 = 1 << 49,
    _Align1Shl50 = 1 << 50,
    _Align1Shl51 = 1 << 51,
    _Align1Shl52 = 1 << 52,
    _Align1Shl53 = 1 << 53,
    _Align1Shl54 = 1 << 54,
    _Align1Shl55 = 1 << 55,
    _Align1Shl56 = 1 << 56,
    _Align1Shl57 = 1 << 57,
    _Align1Shl58 = 1 << 58,
    _Align1Shl59 = 1 << 59,
    _Align1Shl60 = 1 << 60,
    _Align1Shl61 = 1 << 61,
    _Align1Shl62 = 1 << 62,
    _Align1Shl63 = 1 << 63,
}