core/ptr/
mut_ptr.rs

1use super::*;
2use crate::cmp::Ordering::{Equal, Greater, Less};
3use crate::intrinsics::const_eval_select;
4use crate::mem::SizedTypeProperties;
5use crate::slice::{self, SliceIndex};
6
7impl<T: ?Sized> *mut T {
8    /// Returns `true` if the pointer is null.
9    ///
10    /// Note that unsized types have many possible null pointers, as only the
11    /// raw data pointer is considered, not their length, vtable, etc.
12    /// Therefore, two pointers that are null may still not compare equal to
13    /// each other.
14    ///
15    /// # Panics during const evaluation
16    ///
17    /// If this method is used during const evaluation, and `self` is a pointer
18    /// that is offset beyond the bounds of the memory it initially pointed to,
19    /// then there might not be enough information to determine whether the
20    /// pointer is null. This is because the absolute address in memory is not
21    /// known at compile time. If the nullness of the pointer cannot be
22    /// determined, this method will panic.
23    ///
24    /// In-bounds pointers are never null, so the method will never panic for
25    /// such pointers.
26    ///
27    /// # Examples
28    ///
29    /// ```
30    /// let mut s = [1, 2, 3];
31    /// let ptr: *mut u32 = s.as_mut_ptr();
32    /// assert!(!ptr.is_null());
33    /// ```
34    #[stable(feature = "rust1", since = "1.0.0")]
35    #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")]
36    #[rustc_diagnostic_item = "ptr_is_null"]
37    #[inline]
38    pub const fn is_null(self) -> bool {
39        self.cast_const().is_null()
40    }
41
42    /// Casts to a pointer of another type.
43    #[stable(feature = "ptr_cast", since = "1.38.0")]
44    #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
45    #[rustc_diagnostic_item = "ptr_cast"]
46    #[inline(always)]
47    pub const fn cast<U>(self) -> *mut U {
48        self as _
49    }
50
51    /// Uses the address value in a new pointer of another type.
52    ///
53    /// This operation will ignore the address part of its `meta` operand and discard existing
54    /// metadata of `self`. For pointers to a sized types (thin pointers), this has the same effect
55    /// as a simple cast. For pointers to an unsized type (fat pointers) this recombines the address
56    /// with new metadata such as slice lengths or `dyn`-vtable.
57    ///
58    /// The resulting pointer will have provenance of `self`. This operation is semantically the
59    /// same as creating a new pointer with the data pointer value of `self` but the metadata of
60    /// `meta`, being fat or thin depending on the `meta` operand.
61    ///
62    /// # Examples
63    ///
64    /// This function is primarily useful for enabling pointer arithmetic on potentially fat
65    /// pointers. The pointer is cast to a sized pointee to utilize offset operations and then
66    /// recombined with its own original metadata.
67    ///
68    /// ```
69    /// #![feature(set_ptr_value)]
70    /// # use core::fmt::Debug;
71    /// let mut arr: [i32; 3] = [1, 2, 3];
72    /// let mut ptr = arr.as_mut_ptr() as *mut dyn Debug;
73    /// let thin = ptr as *mut u8;
74    /// unsafe {
75    ///     ptr = thin.add(8).with_metadata_of(ptr);
76    ///     # assert_eq!(*(ptr as *mut i32), 3);
77    ///     println!("{:?}", &*ptr); // will print "3"
78    /// }
79    /// ```
80    ///
81    /// # *Incorrect* usage
82    ///
83    /// The provenance from pointers is *not* combined. The result must only be used to refer to the
84    /// address allowed by `self`.
85    ///
86    /// ```rust,no_run
87    /// #![feature(set_ptr_value)]
88    /// let mut x = 0u32;
89    /// let mut y = 1u32;
90    ///
91    /// let x = (&mut x) as *mut u32;
92    /// let y = (&mut y) as *mut u32;
93    ///
94    /// let offset = (x as usize - y as usize) / 4;
95    /// let bad = x.wrapping_add(offset).with_metadata_of(y);
96    ///
97    /// // This dereference is UB. The pointer only has provenance for `x` but points to `y`.
98    /// println!("{:?}", unsafe { &*bad });
99    #[unstable(feature = "set_ptr_value", issue = "75091")]
100    #[must_use = "returns a new pointer rather than modifying its argument"]
101    #[inline]
102    pub const fn with_metadata_of<U>(self, meta: *const U) -> *mut U
103    where
104        U: ?Sized,
105    {
106        from_raw_parts_mut::<U>(self as *mut (), metadata(meta))
107    }
108
109    /// Changes constness without changing the type.
110    ///
111    /// This is a bit safer than `as` because it wouldn't silently change the type if the code is
112    /// refactored.
113    ///
114    /// While not strictly required (`*mut T` coerces to `*const T`), this is provided for symmetry
115    /// with [`cast_mut`] on `*const T` and may have documentation value if used instead of implicit
116    /// coercion.
117    ///
118    /// [`cast_mut`]: pointer::cast_mut
119    #[stable(feature = "ptr_const_cast", since = "1.65.0")]
120    #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
121    #[rustc_diagnostic_item = "ptr_cast_const"]
122    #[inline(always)]
123    pub const fn cast_const(self) -> *const T {
124        self as _
125    }
126
127    /// Gets the "address" portion of the pointer.
128    ///
129    /// This is similar to `self as usize`, except that the [provenance][crate::ptr#provenance] of
130    /// the pointer is discarded and not [exposed][crate::ptr#exposed-provenance]. This means that
131    /// casting the returned address back to a pointer yields a [pointer without
132    /// provenance][without_provenance_mut], which is undefined behavior to dereference. To properly
133    /// restore the lost information and obtain a dereferenceable pointer, use
134    /// [`with_addr`][pointer::with_addr] or [`map_addr`][pointer::map_addr].
135    ///
136    /// If using those APIs is not possible because there is no way to preserve a pointer with the
137    /// required provenance, then Strict Provenance might not be for you. Use pointer-integer casts
138    /// or [`expose_provenance`][pointer::expose_provenance] and [`with_exposed_provenance`][with_exposed_provenance]
139    /// instead. However, note that this makes your code less portable and less amenable to tools
140    /// that check for compliance with the Rust memory model.
141    ///
142    /// On most platforms this will produce a value with the same bytes as the original
143    /// pointer, because all the bytes are dedicated to describing the address.
144    /// Platforms which need to store additional information in the pointer may
145    /// perform a change of representation to produce a value containing only the address
146    /// portion of the pointer. What that means is up to the platform to define.
147    ///
148    /// This is a [Strict Provenance][crate::ptr#strict-provenance] API.
149    #[must_use]
150    #[inline(always)]
151    #[stable(feature = "strict_provenance", since = "1.84.0")]
152    pub fn addr(self) -> usize {
153        // A pointer-to-integer transmute currently has exactly the right semantics: it returns the
154        // address without exposing the provenance. Note that this is *not* a stable guarantee about
155        // transmute semantics, it relies on sysroot crates having special status.
156        // SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the
157        // provenance).
158        unsafe { mem::transmute(self.cast::<()>()) }
159    }
160
161    /// Exposes the ["provenance"][crate::ptr#provenance] part of the pointer for future use in
162    /// [`with_exposed_provenance_mut`] and returns the "address" portion.
163    ///
164    /// This is equivalent to `self as usize`, which semantically discards provenance information.
165    /// Furthermore, this (like the `as` cast) has the implicit side-effect of marking the
166    /// provenance as 'exposed', so on platforms that support it you can later call
167    /// [`with_exposed_provenance_mut`] to reconstitute the original pointer including its provenance.
168    ///
169    /// Due to its inherent ambiguity, [`with_exposed_provenance_mut`] may not be supported by tools
170    /// that help you to stay conformant with the Rust memory model. It is recommended to use
171    /// [Strict Provenance][crate::ptr#strict-provenance] APIs such as [`with_addr`][pointer::with_addr]
172    /// wherever possible, in which case [`addr`][pointer::addr] should be used instead of `expose_provenance`.
173    ///
174    /// On most platforms this will produce a value with the same bytes as the original pointer,
175    /// because all the bytes are dedicated to describing the address. Platforms which need to store
176    /// additional information in the pointer may not support this operation, since the 'expose'
177    /// side-effect which is required for [`with_exposed_provenance_mut`] to work is typically not
178    /// available.
179    ///
180    /// This is an [Exposed Provenance][crate::ptr#exposed-provenance] API.
181    ///
182    /// [`with_exposed_provenance_mut`]: with_exposed_provenance_mut
183    #[inline(always)]
184    #[stable(feature = "exposed_provenance", since = "1.84.0")]
185    pub fn expose_provenance(self) -> usize {
186        self.cast::<()>() as usize
187    }
188
189    /// Creates a new pointer with the given address and the [provenance][crate::ptr#provenance] of
190    /// `self`.
191    ///
192    /// This is similar to a `addr as *mut T` cast, but copies
193    /// the *provenance* of `self` to the new pointer.
194    /// This avoids the inherent ambiguity of the unary cast.
195    ///
196    /// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset
197    /// `self` to the given address, and therefore has all the same capabilities and restrictions.
198    ///
199    /// This is a [Strict Provenance][crate::ptr#strict-provenance] API.
200    #[must_use]
201    #[inline]
202    #[stable(feature = "strict_provenance", since = "1.84.0")]
203    pub fn with_addr(self, addr: usize) -> Self {
204        // This should probably be an intrinsic to avoid doing any sort of arithmetic, but
205        // meanwhile, we can implement it with `wrapping_offset`, which preserves the pointer's
206        // provenance.
207        let self_addr = self.addr() as isize;
208        let dest_addr = addr as isize;
209        let offset = dest_addr.wrapping_sub(self_addr);
210        self.wrapping_byte_offset(offset)
211    }
212
213    /// Creates a new pointer by mapping `self`'s address to a new one, preserving the original
214    /// pointer's [provenance][crate::ptr#provenance].
215    ///
216    /// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details.
217    ///
218    /// This is a [Strict Provenance][crate::ptr#strict-provenance] API.
219    #[must_use]
220    #[inline]
221    #[stable(feature = "strict_provenance", since = "1.84.0")]
222    pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self {
223        self.with_addr(f(self.addr()))
224    }
225
226    /// Decompose a (possibly wide) pointer into its data pointer and metadata components.
227    ///
228    /// The pointer can be later reconstructed with [`from_raw_parts_mut`].
229    #[unstable(feature = "ptr_metadata", issue = "81513")]
230    #[inline]
231    pub const fn to_raw_parts(self) -> (*mut (), <T as super::Pointee>::Metadata) {
232        (self.cast(), super::metadata(self))
233    }
234
235    /// Returns `None` if the pointer is null, or else returns a shared reference to
236    /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
237    /// must be used instead.
238    ///
239    /// For the mutable counterpart see [`as_mut`].
240    ///
241    /// [`as_uninit_ref`]: pointer#method.as_uninit_ref-1
242    /// [`as_mut`]: #method.as_mut
243    ///
244    /// # Safety
245    ///
246    /// When calling this method, you have to ensure that *either* the pointer is null *or*
247    /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
248    ///
249    /// # Panics during const evaluation
250    ///
251    /// This method will panic during const evaluation if the pointer cannot be
252    /// determined to be null or not. See [`is_null`] for more information.
253    ///
254    /// [`is_null`]: #method.is_null-1
255    ///
256    /// # Examples
257    ///
258    /// ```
259    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
260    ///
261    /// unsafe {
262    ///     if let Some(val_back) = ptr.as_ref() {
263    ///         println!("We got back the value: {val_back}!");
264    ///     }
265    /// }
266    /// ```
267    ///
268    /// # Null-unchecked version
269    ///
270    /// If you are sure the pointer can never be null and are looking for some kind of
271    /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
272    /// dereference the pointer directly.
273    ///
274    /// ```
275    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
276    ///
277    /// unsafe {
278    ///     let val_back = &*ptr;
279    ///     println!("We got back the value: {val_back}!");
280    /// }
281    /// ```
282    #[stable(feature = "ptr_as_ref", since = "1.9.0")]
283    #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")]
284    #[inline]
285    pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
286        // SAFETY: the caller must guarantee that `self` is valid for a
287        // reference if it isn't null.
288        if self.is_null() { None } else { unsafe { Some(&*self) } }
289    }
290
291    /// Returns a shared reference to the value behind the pointer.
292    /// If the pointer may be null or the value may be uninitialized, [`as_uninit_ref`] must be used instead.
293    /// If the pointer may be null, but the value is known to have been initialized, [`as_ref`] must be used instead.
294    ///
295    /// For the mutable counterpart see [`as_mut_unchecked`].
296    ///
297    /// [`as_ref`]: #method.as_ref
298    /// [`as_uninit_ref`]: #method.as_uninit_ref
299    /// [`as_mut_unchecked`]: #method.as_mut_unchecked
300    ///
301    /// # Safety
302    ///
303    /// When calling this method, you have to ensure that the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
304    ///
305    /// # Examples
306    ///
307    /// ```
308    /// #![feature(ptr_as_ref_unchecked)]
309    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
310    ///
311    /// unsafe {
312    ///     println!("We got back the value: {}!", ptr.as_ref_unchecked());
313    /// }
314    /// ```
315    // FIXME: mention it in the docs for `as_ref` and `as_uninit_ref` once stabilized.
316    #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
317    #[inline]
318    #[must_use]
319    pub const unsafe fn as_ref_unchecked<'a>(self) -> &'a T {
320        // SAFETY: the caller must guarantee that `self` is valid for a reference
321        unsafe { &*self }
322    }
323
324    /// Returns `None` if the pointer is null, or else returns a shared reference to
325    /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
326    /// that the value has to be initialized.
327    ///
328    /// For the mutable counterpart see [`as_uninit_mut`].
329    ///
330    /// [`as_ref`]: pointer#method.as_ref-1
331    /// [`as_uninit_mut`]: #method.as_uninit_mut
332    ///
333    /// # Safety
334    ///
335    /// When calling this method, you have to ensure that *either* the pointer is null *or*
336    /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
337    /// Note that because the created reference is to `MaybeUninit<T>`, the
338    /// source pointer can point to uninitialized memory.
339    ///
340    /// # Panics during const evaluation
341    ///
342    /// This method will panic during const evaluation if the pointer cannot be
343    /// determined to be null or not. See [`is_null`] for more information.
344    ///
345    /// [`is_null`]: #method.is_null-1
346    ///
347    /// # Examples
348    ///
349    /// ```
350    /// #![feature(ptr_as_uninit)]
351    ///
352    /// let ptr: *mut u8 = &mut 10u8 as *mut u8;
353    ///
354    /// unsafe {
355    ///     if let Some(val_back) = ptr.as_uninit_ref() {
356    ///         println!("We got back the value: {}!", val_back.assume_init());
357    ///     }
358    /// }
359    /// ```
360    #[inline]
361    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
362    pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
363    where
364        T: Sized,
365    {
366        // SAFETY: the caller must guarantee that `self` meets all the
367        // requirements for a reference.
368        if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
369    }
370
371    /// Adds a signed offset to a pointer.
372    ///
373    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
374    /// offset of `3 * size_of::<T>()` bytes.
375    ///
376    /// # Safety
377    ///
378    /// If any of the following conditions are violated, the result is Undefined Behavior:
379    ///
380    /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
381    ///   "wrapping around"), must fit in an `isize`.
382    ///
383    /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
384    ///   [allocated object], and the entire memory range between `self` and the result must be in
385    ///   bounds of that allocated object. In particular, this range must not "wrap around" the edge
386    ///   of the address space.
387    ///
388    /// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
389    /// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
390    /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
391    /// safe.
392    ///
393    /// Consider using [`wrapping_offset`] instead if these constraints are
394    /// difficult to satisfy. The only advantage of this method is that it
395    /// enables more aggressive compiler optimizations.
396    ///
397    /// [`wrapping_offset`]: #method.wrapping_offset
398    /// [allocated object]: crate::ptr#allocated-object
399    ///
400    /// # Examples
401    ///
402    /// ```
403    /// let mut s = [1, 2, 3];
404    /// let ptr: *mut u32 = s.as_mut_ptr();
405    ///
406    /// unsafe {
407    ///     assert_eq!(2, *ptr.offset(1));
408    ///     assert_eq!(3, *ptr.offset(2));
409    /// }
410    /// ```
411    #[stable(feature = "rust1", since = "1.0.0")]
412    #[must_use = "returns a new pointer rather than modifying its argument"]
413    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
414    #[inline(always)]
415    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
416    pub const unsafe fn offset(self, count: isize) -> *mut T
417    where
418        T: Sized,
419    {
420        #[inline]
421        #[rustc_allow_const_fn_unstable(const_eval_select)]
422        const fn runtime_offset_nowrap(this: *const (), count: isize, size: usize) -> bool {
423            // We can use const_eval_select here because this is only for UB checks.
424            const_eval_select!(
425                @capture { this: *const (), count: isize, size: usize } -> bool:
426                if const {
427                    true
428                } else {
429                    // `size` is the size of a Rust type, so we know that
430                    // `size <= isize::MAX` and thus `as` cast here is not lossy.
431                    let Some(byte_offset) = count.checked_mul(size as isize) else {
432                        return false;
433                    };
434                    let (_, overflow) = this.addr().overflowing_add_signed(byte_offset);
435                    !overflow
436                }
437            )
438        }
439
440        ub_checks::assert_unsafe_precondition!(
441            check_language_ub,
442            "ptr::offset requires the address calculation to not overflow",
443            (
444                this: *const () = self as *const (),
445                count: isize = count,
446                size: usize = size_of::<T>(),
447            ) => runtime_offset_nowrap(this, count, size)
448        );
449
450        // SAFETY: the caller must uphold the safety contract for `offset`.
451        // The obtained pointer is valid for writes since the caller must
452        // guarantee that it points to the same allocated object as `self`.
453        unsafe { intrinsics::offset(self, count) }
454    }
455
456    /// Adds a signed offset in bytes to a pointer.
457    ///
458    /// `count` is in units of **bytes**.
459    ///
460    /// This is purely a convenience for casting to a `u8` pointer and
461    /// using [offset][pointer::offset] on it. See that method for documentation
462    /// and safety requirements.
463    ///
464    /// For non-`Sized` pointees this operation changes only the data pointer,
465    /// leaving the metadata untouched.
466    #[must_use]
467    #[inline(always)]
468    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
469    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
470    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
471    pub const unsafe fn byte_offset(self, count: isize) -> Self {
472        // SAFETY: the caller must uphold the safety contract for `offset`.
473        unsafe { self.cast::<u8>().offset(count).with_metadata_of(self) }
474    }
475
476    /// Adds a signed offset to a pointer using wrapping arithmetic.
477    ///
478    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
479    /// offset of `3 * size_of::<T>()` bytes.
480    ///
481    /// # Safety
482    ///
483    /// This operation itself is always safe, but using the resulting pointer is not.
484    ///
485    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
486    /// be used to read or write other allocated objects.
487    ///
488    /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
489    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
490    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
491    /// `x` and `y` point into the same allocated object.
492    ///
493    /// Compared to [`offset`], this method basically delays the requirement of staying within the
494    /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
495    /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
496    /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
497    /// can be optimized better and is thus preferable in performance-sensitive code.
498    ///
499    /// The delayed check only considers the value of the pointer that was dereferenced, not the
500    /// intermediate values used during the computation of the final result. For example,
501    /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
502    /// words, leaving the allocated object and then re-entering it later is permitted.
503    ///
504    /// [`offset`]: #method.offset
505    /// [allocated object]: crate::ptr#allocated-object
506    ///
507    /// # Examples
508    ///
509    /// ```
510    /// // Iterate using a raw pointer in increments of two elements
511    /// let mut data = [1u8, 2, 3, 4, 5];
512    /// let mut ptr: *mut u8 = data.as_mut_ptr();
513    /// let step = 2;
514    /// let end_rounded_up = ptr.wrapping_offset(6);
515    ///
516    /// while ptr != end_rounded_up {
517    ///     unsafe {
518    ///         *ptr = 0;
519    ///     }
520    ///     ptr = ptr.wrapping_offset(step);
521    /// }
522    /// assert_eq!(&data, &[0, 2, 0, 4, 0]);
523    /// ```
524    #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
525    #[must_use = "returns a new pointer rather than modifying its argument"]
526    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
527    #[inline(always)]
528    pub const fn wrapping_offset(self, count: isize) -> *mut T
529    where
530        T: Sized,
531    {
532        // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called.
533        unsafe { intrinsics::arith_offset(self, count) as *mut T }
534    }
535
536    /// Adds a signed offset in bytes to a pointer using wrapping arithmetic.
537    ///
538    /// `count` is in units of **bytes**.
539    ///
540    /// This is purely a convenience for casting to a `u8` pointer and
541    /// using [wrapping_offset][pointer::wrapping_offset] on it. See that method
542    /// for documentation.
543    ///
544    /// For non-`Sized` pointees this operation changes only the data pointer,
545    /// leaving the metadata untouched.
546    #[must_use]
547    #[inline(always)]
548    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
549    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
550    pub const fn wrapping_byte_offset(self, count: isize) -> Self {
551        self.cast::<u8>().wrapping_offset(count).with_metadata_of(self)
552    }
553
554    /// Masks out bits of the pointer according to a mask.
555    ///
556    /// This is convenience for `ptr.map_addr(|a| a & mask)`.
557    ///
558    /// For non-`Sized` pointees this operation changes only the data pointer,
559    /// leaving the metadata untouched.
560    ///
561    /// ## Examples
562    ///
563    /// ```
564    /// #![feature(ptr_mask)]
565    /// let mut v = 17_u32;
566    /// let ptr: *mut u32 = &mut v;
567    ///
568    /// // `u32` is 4 bytes aligned,
569    /// // which means that lower 2 bits are always 0.
570    /// let tag_mask = 0b11;
571    /// let ptr_mask = !tag_mask;
572    ///
573    /// // We can store something in these lower bits
574    /// let tagged_ptr = ptr.map_addr(|a| a | 0b10);
575    ///
576    /// // Get the "tag" back
577    /// let tag = tagged_ptr.addr() & tag_mask;
578    /// assert_eq!(tag, 0b10);
579    ///
580    /// // Note that `tagged_ptr` is unaligned, it's UB to read from/write to it.
581    /// // To get original pointer `mask` can be used:
582    /// let masked_ptr = tagged_ptr.mask(ptr_mask);
583    /// assert_eq!(unsafe { *masked_ptr }, 17);
584    ///
585    /// unsafe { *masked_ptr = 0 };
586    /// assert_eq!(v, 0);
587    /// ```
588    #[unstable(feature = "ptr_mask", issue = "98290")]
589    #[must_use = "returns a new pointer rather than modifying its argument"]
590    #[inline(always)]
591    pub fn mask(self, mask: usize) -> *mut T {
592        intrinsics::ptr_mask(self.cast::<()>(), mask).cast_mut().with_metadata_of(self)
593    }
594
595    /// Returns `None` if the pointer is null, or else returns a unique reference to
596    /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
597    /// must be used instead.
598    ///
599    /// For the shared counterpart see [`as_ref`].
600    ///
601    /// [`as_uninit_mut`]: #method.as_uninit_mut
602    /// [`as_ref`]: pointer#method.as_ref-1
603    ///
604    /// # Safety
605    ///
606    /// When calling this method, you have to ensure that *either*
607    /// the pointer is null *or*
608    /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
609    ///
610    /// # Panics during const evaluation
611    ///
612    /// This method will panic during const evaluation if the pointer cannot be
613    /// determined to be null or not. See [`is_null`] for more information.
614    ///
615    /// [`is_null`]: #method.is_null-1
616    ///
617    /// # Examples
618    ///
619    /// ```
620    /// let mut s = [1, 2, 3];
621    /// let ptr: *mut u32 = s.as_mut_ptr();
622    /// let first_value = unsafe { ptr.as_mut().unwrap() };
623    /// *first_value = 4;
624    /// # assert_eq!(s, [4, 2, 3]);
625    /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
626    /// ```
627    ///
628    /// # Null-unchecked version
629    ///
630    /// If you are sure the pointer can never be null and are looking for some kind of
631    /// `as_mut_unchecked` that returns the `&mut T` instead of `Option<&mut T>`, know that
632    /// you can dereference the pointer directly.
633    ///
634    /// ```
635    /// let mut s = [1, 2, 3];
636    /// let ptr: *mut u32 = s.as_mut_ptr();
637    /// let first_value = unsafe { &mut *ptr };
638    /// *first_value = 4;
639    /// # assert_eq!(s, [4, 2, 3]);
640    /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
641    /// ```
642    #[stable(feature = "ptr_as_ref", since = "1.9.0")]
643    #[rustc_const_stable(feature = "const_ptr_is_null", since = "1.84.0")]
644    #[inline]
645    pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T> {
646        // SAFETY: the caller must guarantee that `self` is be valid for
647        // a mutable reference if it isn't null.
648        if self.is_null() { None } else { unsafe { Some(&mut *self) } }
649    }
650
651    /// Returns a unique reference to the value behind the pointer.
652    /// If the pointer may be null or the value may be uninitialized, [`as_uninit_mut`] must be used instead.
653    /// If the pointer may be null, but the value is known to have been initialized, [`as_mut`] must be used instead.
654    ///
655    /// For the shared counterpart see [`as_ref_unchecked`].
656    ///
657    /// [`as_mut`]: #method.as_mut
658    /// [`as_uninit_mut`]: #method.as_uninit_mut
659    /// [`as_ref_unchecked`]: #method.as_mut_unchecked
660    ///
661    /// # Safety
662    ///
663    /// When calling this method, you have to ensure that
664    /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
665    ///
666    /// # Examples
667    ///
668    /// ```
669    /// #![feature(ptr_as_ref_unchecked)]
670    /// let mut s = [1, 2, 3];
671    /// let ptr: *mut u32 = s.as_mut_ptr();
672    /// let first_value = unsafe { ptr.as_mut_unchecked() };
673    /// *first_value = 4;
674    /// # assert_eq!(s, [4, 2, 3]);
675    /// println!("{s:?}"); // It'll print: "[4, 2, 3]".
676    /// ```
677    // FIXME: mention it in the docs for `as_mut` and `as_uninit_mut` once stabilized.
678    #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")]
679    #[inline]
680    #[must_use]
681    pub const unsafe fn as_mut_unchecked<'a>(self) -> &'a mut T {
682        // SAFETY: the caller must guarantee that `self` is valid for a reference
683        unsafe { &mut *self }
684    }
685
686    /// Returns `None` if the pointer is null, or else returns a unique reference to
687    /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
688    /// that the value has to be initialized.
689    ///
690    /// For the shared counterpart see [`as_uninit_ref`].
691    ///
692    /// [`as_mut`]: #method.as_mut
693    /// [`as_uninit_ref`]: pointer#method.as_uninit_ref-1
694    ///
695    /// # Safety
696    ///
697    /// When calling this method, you have to ensure that *either* the pointer is null *or*
698    /// the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion).
699    ///
700    /// # Panics during const evaluation
701    ///
702    /// This method will panic during const evaluation if the pointer cannot be
703    /// determined to be null or not. See [`is_null`] for more information.
704    ///
705    /// [`is_null`]: #method.is_null-1
706    #[inline]
707    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
708    pub const unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
709    where
710        T: Sized,
711    {
712        // SAFETY: the caller must guarantee that `self` meets all the
713        // requirements for a reference.
714        if self.is_null() { None } else { Some(unsafe { &mut *(self as *mut MaybeUninit<T>) }) }
715    }
716
717    /// Returns whether two pointers are guaranteed to be equal.
718    ///
719    /// At runtime this function behaves like `Some(self == other)`.
720    /// However, in some contexts (e.g., compile-time evaluation),
721    /// it is not always possible to determine equality of two pointers, so this function may
722    /// spuriously return `None` for pointers that later actually turn out to have its equality known.
723    /// But when it returns `Some`, the pointers' equality is guaranteed to be known.
724    ///
725    /// The return value may change from `Some` to `None` and vice versa depending on the compiler
726    /// version and unsafe code must not
727    /// rely on the result of this function for soundness. It is suggested to only use this function
728    /// for performance optimizations where spurious `None` return values by this function do not
729    /// affect the outcome, but just the performance.
730    /// The consequences of using this method to make runtime and compile-time code behave
731    /// differently have not been explored. This method should not be used to introduce such
732    /// differences, and it should also not be stabilized before we have a better understanding
733    /// of this issue.
734    #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
735    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
736    #[inline]
737    pub const fn guaranteed_eq(self, other: *mut T) -> Option<bool>
738    where
739        T: Sized,
740    {
741        (self as *const T).guaranteed_eq(other as _)
742    }
743
744    /// Returns whether two pointers are guaranteed to be inequal.
745    ///
746    /// At runtime this function behaves like `Some(self != other)`.
747    /// However, in some contexts (e.g., compile-time evaluation),
748    /// it is not always possible to determine inequality of two pointers, so this function may
749    /// spuriously return `None` for pointers that later actually turn out to have its inequality known.
750    /// But when it returns `Some`, the pointers' inequality is guaranteed to be known.
751    ///
752    /// The return value may change from `Some` to `None` and vice versa depending on the compiler
753    /// version and unsafe code must not
754    /// rely on the result of this function for soundness. It is suggested to only use this function
755    /// for performance optimizations where spurious `None` return values by this function do not
756    /// affect the outcome, but just the performance.
757    /// The consequences of using this method to make runtime and compile-time code behave
758    /// differently have not been explored. This method should not be used to introduce such
759    /// differences, and it should also not be stabilized before we have a better understanding
760    /// of this issue.
761    #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
762    #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
763    #[inline]
764    pub const fn guaranteed_ne(self, other: *mut T) -> Option<bool>
765    where
766        T: Sized,
767    {
768        (self as *const T).guaranteed_ne(other as _)
769    }
770
771    /// Calculates the distance between two pointers within the same allocation. The returned value is in
772    /// units of T: the distance in bytes divided by `mem::size_of::<T>()`.
773    ///
774    /// This is equivalent to `(self as isize - origin as isize) / (mem::size_of::<T>() as isize)`,
775    /// except that it has a lot more opportunities for UB, in exchange for the compiler
776    /// better understanding what you are doing.
777    ///
778    /// The primary motivation of this method is for computing the `len` of an array/slice
779    /// of `T` that you are currently representing as a "start" and "end" pointer
780    /// (and "end" is "one past the end" of the array).
781    /// In that case, `end.offset_from(start)` gets you the length of the array.
782    ///
783    /// All of the following safety requirements are trivially satisfied for this usecase.
784    ///
785    /// [`offset`]: pointer#method.offset-1
786    ///
787    /// # Safety
788    ///
789    /// If any of the following conditions are violated, the result is Undefined Behavior:
790    ///
791    /// * `self` and `origin` must either
792    ///
793    ///   * point to the same address, or
794    ///   * both be [derived from][crate::ptr#provenance] a pointer to the same [allocated object], and the memory range between
795    ///     the two pointers must be in bounds of that object. (See below for an example.)
796    ///
797    /// * The distance between the pointers, in bytes, must be an exact multiple
798    ///   of the size of `T`.
799    ///
800    /// As a consequence, the absolute distance between the pointers, in bytes, computed on
801    /// mathematical integers (without "wrapping around"), cannot overflow an `isize`. This is
802    /// implied by the in-bounds requirement, and the fact that no allocated object can be larger
803    /// than `isize::MAX` bytes.
804    ///
805    /// The requirement for pointers to be derived from the same allocated object is primarily
806    /// needed for `const`-compatibility: the distance between pointers into *different* allocated
807    /// objects is not known at compile-time. However, the requirement also exists at
808    /// runtime and may be exploited by optimizations. If you wish to compute the difference between
809    /// pointers that are not guaranteed to be from the same allocation, use `(self as isize -
810    /// origin as isize) / mem::size_of::<T>()`.
811    // FIXME: recommend `addr()` instead of `as usize` once that is stable.
812    ///
813    /// [`add`]: #method.add
814    /// [allocated object]: crate::ptr#allocated-object
815    ///
816    /// # Panics
817    ///
818    /// This function panics if `T` is a Zero-Sized Type ("ZST").
819    ///
820    /// # Examples
821    ///
822    /// Basic usage:
823    ///
824    /// ```
825    /// let mut a = [0; 5];
826    /// let ptr1: *mut i32 = &mut a[1];
827    /// let ptr2: *mut i32 = &mut a[3];
828    /// unsafe {
829    ///     assert_eq!(ptr2.offset_from(ptr1), 2);
830    ///     assert_eq!(ptr1.offset_from(ptr2), -2);
831    ///     assert_eq!(ptr1.offset(2), ptr2);
832    ///     assert_eq!(ptr2.offset(-2), ptr1);
833    /// }
834    /// ```
835    ///
836    /// *Incorrect* usage:
837    ///
838    /// ```rust,no_run
839    /// let ptr1 = Box::into_raw(Box::new(0u8));
840    /// let ptr2 = Box::into_raw(Box::new(1u8));
841    /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize);
842    /// // Make ptr2_other an "alias" of ptr2.add(1), but derived from ptr1.
843    /// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff).wrapping_offset(1);
844    /// assert_eq!(ptr2 as usize, ptr2_other as usize);
845    /// // Since ptr2_other and ptr2 are derived from pointers to different objects,
846    /// // computing their offset is undefined behavior, even though
847    /// // they point to addresses that are in-bounds of the same object!
848    /// unsafe {
849    ///     let one = ptr2_other.offset_from(ptr2); // Undefined Behavior! ⚠️
850    /// }
851    /// ```
852    #[stable(feature = "ptr_offset_from", since = "1.47.0")]
853    #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")]
854    #[inline(always)]
855    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
856    pub const unsafe fn offset_from(self, origin: *const T) -> isize
857    where
858        T: Sized,
859    {
860        // SAFETY: the caller must uphold the safety contract for `offset_from`.
861        unsafe { (self as *const T).offset_from(origin) }
862    }
863
864    /// Calculates the distance between two pointers within the same allocation. The returned value is in
865    /// units of **bytes**.
866    ///
867    /// This is purely a convenience for casting to a `u8` pointer and
868    /// using [`offset_from`][pointer::offset_from] on it. See that method for
869    /// documentation and safety requirements.
870    ///
871    /// For non-`Sized` pointees this operation considers only the data pointers,
872    /// ignoring the metadata.
873    #[inline(always)]
874    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
875    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
876    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
877    pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize {
878        // SAFETY: the caller must uphold the safety contract for `offset_from`.
879        unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) }
880    }
881
882    /// Calculates the distance between two pointers within the same allocation, *where it's known that
883    /// `self` is equal to or greater than `origin`*. The returned value is in
884    /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`.
885    ///
886    /// This computes the same value that [`offset_from`](#method.offset_from)
887    /// would compute, but with the added precondition that the offset is
888    /// guaranteed to be non-negative.  This method is equivalent to
889    /// `usize::try_from(self.offset_from(origin)).unwrap_unchecked()`,
890    /// but it provides slightly more information to the optimizer, which can
891    /// sometimes allow it to optimize slightly better with some backends.
892    ///
893    /// This method can be thought of as recovering the `count` that was passed
894    /// to [`add`](#method.add) (or, with the parameters in the other order,
895    /// to [`sub`](#method.sub)).  The following are all equivalent, assuming
896    /// that their safety preconditions are met:
897    /// ```rust
898    /// # #![feature(ptr_sub_ptr)]
899    /// # unsafe fn blah(ptr: *mut i32, origin: *mut i32, count: usize) -> bool {
900    /// ptr.sub_ptr(origin) == count
901    /// # &&
902    /// origin.add(count) == ptr
903    /// # &&
904    /// ptr.sub(count) == origin
905    /// # }
906    /// ```
907    ///
908    /// # Safety
909    ///
910    /// - The distance between the pointers must be non-negative (`self >= origin`)
911    ///
912    /// - *All* the safety conditions of [`offset_from`](#method.offset_from)
913    ///   apply to this method as well; see it for the full details.
914    ///
915    /// Importantly, despite the return type of this method being able to represent
916    /// a larger offset, it's still *not permitted* to pass pointers which differ
917    /// by more than `isize::MAX` *bytes*.  As such, the result of this method will
918    /// always be less than or equal to `isize::MAX as usize`.
919    ///
920    /// # Panics
921    ///
922    /// This function panics if `T` is a Zero-Sized Type ("ZST").
923    ///
924    /// # Examples
925    ///
926    /// ```
927    /// #![feature(ptr_sub_ptr)]
928    ///
929    /// let mut a = [0; 5];
930    /// let p: *mut i32 = a.as_mut_ptr();
931    /// unsafe {
932    ///     let ptr1: *mut i32 = p.add(1);
933    ///     let ptr2: *mut i32 = p.add(3);
934    ///
935    ///     assert_eq!(ptr2.sub_ptr(ptr1), 2);
936    ///     assert_eq!(ptr1.add(2), ptr2);
937    ///     assert_eq!(ptr2.sub(2), ptr1);
938    ///     assert_eq!(ptr2.sub_ptr(ptr2), 0);
939    /// }
940    ///
941    /// // This would be incorrect, as the pointers are not correctly ordered:
942    /// // ptr1.offset_from(ptr2)
943    #[unstable(feature = "ptr_sub_ptr", issue = "95892")]
944    #[rustc_const_unstable(feature = "const_ptr_sub_ptr", issue = "95892")]
945    #[inline]
946    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
947    pub const unsafe fn sub_ptr(self, origin: *const T) -> usize
948    where
949        T: Sized,
950    {
951        // SAFETY: the caller must uphold the safety contract for `sub_ptr`.
952        unsafe { (self as *const T).sub_ptr(origin) }
953    }
954
955    /// Calculates the distance between two pointers within the same allocation, *where it's known that
956    /// `self` is equal to or greater than `origin`*. The returned value is in
957    /// units of **bytes**.
958    ///
959    /// This is purely a convenience for casting to a `u8` pointer and
960    /// using [`sub_ptr`][pointer::sub_ptr] on it. See that method for
961    /// documentation and safety requirements.
962    ///
963    /// For non-`Sized` pointees this operation considers only the data pointers,
964    /// ignoring the metadata.
965    #[unstable(feature = "ptr_sub_ptr", issue = "95892")]
966    #[rustc_const_unstable(feature = "const_ptr_sub_ptr", issue = "95892")]
967    #[inline]
968    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
969    pub const unsafe fn byte_sub_ptr<U: ?Sized>(self, origin: *mut U) -> usize {
970        // SAFETY: the caller must uphold the safety contract for `byte_sub_ptr`.
971        unsafe { (self as *const T).byte_sub_ptr(origin) }
972    }
973
974    /// Adds an unsigned offset to a pointer.
975    ///
976    /// This can only move the pointer forward (or not move it). If you need to move forward or
977    /// backward depending on the value, then you might want [`offset`](#method.offset) instead
978    /// which takes a signed offset.
979    ///
980    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
981    /// offset of `3 * size_of::<T>()` bytes.
982    ///
983    /// # Safety
984    ///
985    /// If any of the following conditions are violated, the result is Undefined Behavior:
986    ///
987    /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
988    ///   "wrapping around"), must fit in an `isize`.
989    ///
990    /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
991    ///   [allocated object], and the entire memory range between `self` and the result must be in
992    ///   bounds of that allocated object. In particular, this range must not "wrap around" the edge
993    ///   of the address space.
994    ///
995    /// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
996    /// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
997    /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
998    /// safe.
999    ///
1000    /// Consider using [`wrapping_add`] instead if these constraints are
1001    /// difficult to satisfy. The only advantage of this method is that it
1002    /// enables more aggressive compiler optimizations.
1003    ///
1004    /// [`wrapping_add`]: #method.wrapping_add
1005    /// [allocated object]: crate::ptr#allocated-object
1006    ///
1007    /// # Examples
1008    ///
1009    /// ```
1010    /// let s: &str = "123";
1011    /// let ptr: *const u8 = s.as_ptr();
1012    ///
1013    /// unsafe {
1014    ///     assert_eq!('2', *ptr.add(1) as char);
1015    ///     assert_eq!('3', *ptr.add(2) as char);
1016    /// }
1017    /// ```
1018    #[stable(feature = "pointer_methods", since = "1.26.0")]
1019    #[must_use = "returns a new pointer rather than modifying its argument"]
1020    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1021    #[inline(always)]
1022    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1023    pub const unsafe fn add(self, count: usize) -> Self
1024    where
1025        T: Sized,
1026    {
1027        #[cfg(debug_assertions)]
1028        #[inline]
1029        #[rustc_allow_const_fn_unstable(const_eval_select)]
1030        const fn runtime_add_nowrap(this: *const (), count: usize, size: usize) -> bool {
1031            const_eval_select!(
1032                @capture { this: *const (), count: usize, size: usize } -> bool:
1033                if const {
1034                    true
1035                } else {
1036                    let Some(byte_offset) = count.checked_mul(size) else {
1037                        return false;
1038                    };
1039                    let (_, overflow) = this.addr().overflowing_add(byte_offset);
1040                    byte_offset <= (isize::MAX as usize) && !overflow
1041                }
1042            )
1043        }
1044
1045        #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
1046        ub_checks::assert_unsafe_precondition!(
1047            check_language_ub,
1048            "ptr::add requires that the address calculation does not overflow",
1049            (
1050                this: *const () = self as *const (),
1051                count: usize = count,
1052                size: usize = size_of::<T>(),
1053            ) => runtime_add_nowrap(this, count, size)
1054        );
1055
1056        // SAFETY: the caller must uphold the safety contract for `offset`.
1057        unsafe { intrinsics::offset(self, count) }
1058    }
1059
1060    /// Adds an unsigned offset in bytes to a pointer.
1061    ///
1062    /// `count` is in units of bytes.
1063    ///
1064    /// This is purely a convenience for casting to a `u8` pointer and
1065    /// using [add][pointer::add] on it. See that method for documentation
1066    /// and safety requirements.
1067    ///
1068    /// For non-`Sized` pointees this operation changes only the data pointer,
1069    /// leaving the metadata untouched.
1070    #[must_use]
1071    #[inline(always)]
1072    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1073    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1074    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1075    pub const unsafe fn byte_add(self, count: usize) -> Self {
1076        // SAFETY: the caller must uphold the safety contract for `add`.
1077        unsafe { self.cast::<u8>().add(count).with_metadata_of(self) }
1078    }
1079
1080    /// Subtracts an unsigned offset from a pointer.
1081    ///
1082    /// This can only move the pointer backward (or not move it). If you need to move forward or
1083    /// backward depending on the value, then you might want [`offset`](#method.offset) instead
1084    /// which takes a signed offset.
1085    ///
1086    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1087    /// offset of `3 * size_of::<T>()` bytes.
1088    ///
1089    /// # Safety
1090    ///
1091    /// If any of the following conditions are violated, the result is Undefined Behavior:
1092    ///
1093    /// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
1094    ///   "wrapping around"), must fit in an `isize`.
1095    ///
1096    /// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
1097    ///   [allocated object], and the entire memory range between `self` and the result must be in
1098    ///   bounds of that allocated object. In particular, this range must not "wrap around" the edge
1099    ///   of the address space.
1100    ///
1101    /// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
1102    /// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
1103    /// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
1104    /// safe.
1105    ///
1106    /// Consider using [`wrapping_sub`] instead if these constraints are
1107    /// difficult to satisfy. The only advantage of this method is that it
1108    /// enables more aggressive compiler optimizations.
1109    ///
1110    /// [`wrapping_sub`]: #method.wrapping_sub
1111    /// [allocated object]: crate::ptr#allocated-object
1112    ///
1113    /// # Examples
1114    ///
1115    /// ```
1116    /// let s: &str = "123";
1117    ///
1118    /// unsafe {
1119    ///     let end: *const u8 = s.as_ptr().add(3);
1120    ///     assert_eq!('3', *end.sub(1) as char);
1121    ///     assert_eq!('2', *end.sub(2) as char);
1122    /// }
1123    /// ```
1124    #[stable(feature = "pointer_methods", since = "1.26.0")]
1125    #[must_use = "returns a new pointer rather than modifying its argument"]
1126    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1127    #[inline(always)]
1128    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1129    pub const unsafe fn sub(self, count: usize) -> Self
1130    where
1131        T: Sized,
1132    {
1133        #[cfg(debug_assertions)]
1134        #[inline]
1135        #[rustc_allow_const_fn_unstable(const_eval_select)]
1136        const fn runtime_sub_nowrap(this: *const (), count: usize, size: usize) -> bool {
1137            const_eval_select!(
1138                @capture { this: *const (), count: usize, size: usize } -> bool:
1139                if const {
1140                    true
1141                } else {
1142                    let Some(byte_offset) = count.checked_mul(size) else {
1143                        return false;
1144                    };
1145                    byte_offset <= (isize::MAX as usize) && this.addr() >= byte_offset
1146                }
1147            )
1148        }
1149
1150        #[cfg(debug_assertions)] // Expensive, and doesn't catch much in the wild.
1151        ub_checks::assert_unsafe_precondition!(
1152            check_language_ub,
1153            "ptr::sub requires that the address calculation does not overflow",
1154            (
1155                this: *const () = self as *const (),
1156                count: usize = count,
1157                size: usize = size_of::<T>(),
1158            ) => runtime_sub_nowrap(this, count, size)
1159        );
1160
1161        if T::IS_ZST {
1162            // Pointer arithmetic does nothing when the pointee is a ZST.
1163            self
1164        } else {
1165            // SAFETY: the caller must uphold the safety contract for `offset`.
1166            // Because the pointee is *not* a ZST, that means that `count` is
1167            // at most `isize::MAX`, and thus the negation cannot overflow.
1168            unsafe { intrinsics::offset(self, intrinsics::unchecked_sub(0, count as isize)) }
1169        }
1170    }
1171
1172    /// Subtracts an unsigned offset in bytes from a pointer.
1173    ///
1174    /// `count` is in units of bytes.
1175    ///
1176    /// This is purely a convenience for casting to a `u8` pointer and
1177    /// using [sub][pointer::sub] on it. See that method for documentation
1178    /// and safety requirements.
1179    ///
1180    /// For non-`Sized` pointees this operation changes only the data pointer,
1181    /// leaving the metadata untouched.
1182    #[must_use]
1183    #[inline(always)]
1184    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1185    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1186    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1187    pub const unsafe fn byte_sub(self, count: usize) -> Self {
1188        // SAFETY: the caller must uphold the safety contract for `sub`.
1189        unsafe { self.cast::<u8>().sub(count).with_metadata_of(self) }
1190    }
1191
1192    /// Adds an unsigned offset to a pointer using wrapping arithmetic.
1193    ///
1194    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1195    /// offset of `3 * size_of::<T>()` bytes.
1196    ///
1197    /// # Safety
1198    ///
1199    /// This operation itself is always safe, but using the resulting pointer is not.
1200    ///
1201    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
1202    /// be used to read or write other allocated objects.
1203    ///
1204    /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
1205    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
1206    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
1207    /// `x` and `y` point into the same allocated object.
1208    ///
1209    /// Compared to [`add`], this method basically delays the requirement of staying within the
1210    /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
1211    /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
1212    /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
1213    /// can be optimized better and is thus preferable in performance-sensitive code.
1214    ///
1215    /// The delayed check only considers the value of the pointer that was dereferenced, not the
1216    /// intermediate values used during the computation of the final result. For example,
1217    /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
1218    /// allocated object and then re-entering it later is permitted.
1219    ///
1220    /// [`add`]: #method.add
1221    /// [allocated object]: crate::ptr#allocated-object
1222    ///
1223    /// # Examples
1224    ///
1225    /// ```
1226    /// // Iterate using a raw pointer in increments of two elements
1227    /// let data = [1u8, 2, 3, 4, 5];
1228    /// let mut ptr: *const u8 = data.as_ptr();
1229    /// let step = 2;
1230    /// let end_rounded_up = ptr.wrapping_add(6);
1231    ///
1232    /// // This loop prints "1, 3, 5, "
1233    /// while ptr != end_rounded_up {
1234    ///     unsafe {
1235    ///         print!("{}, ", *ptr);
1236    ///     }
1237    ///     ptr = ptr.wrapping_add(step);
1238    /// }
1239    /// ```
1240    #[stable(feature = "pointer_methods", since = "1.26.0")]
1241    #[must_use = "returns a new pointer rather than modifying its argument"]
1242    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1243    #[inline(always)]
1244    pub const fn wrapping_add(self, count: usize) -> Self
1245    where
1246        T: Sized,
1247    {
1248        self.wrapping_offset(count as isize)
1249    }
1250
1251    /// Adds an unsigned offset in bytes to a pointer using wrapping arithmetic.
1252    ///
1253    /// `count` is in units of bytes.
1254    ///
1255    /// This is purely a convenience for casting to a `u8` pointer and
1256    /// using [wrapping_add][pointer::wrapping_add] on it. See that method for documentation.
1257    ///
1258    /// For non-`Sized` pointees this operation changes only the data pointer,
1259    /// leaving the metadata untouched.
1260    #[must_use]
1261    #[inline(always)]
1262    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1263    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1264    pub const fn wrapping_byte_add(self, count: usize) -> Self {
1265        self.cast::<u8>().wrapping_add(count).with_metadata_of(self)
1266    }
1267
1268    /// Subtracts an unsigned offset from a pointer using wrapping arithmetic.
1269    ///
1270    /// `count` is in units of T; e.g., a `count` of 3 represents a pointer
1271    /// offset of `3 * size_of::<T>()` bytes.
1272    ///
1273    /// # Safety
1274    ///
1275    /// This operation itself is always safe, but using the resulting pointer is not.
1276    ///
1277    /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not
1278    /// be used to read or write other allocated objects.
1279    ///
1280    /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
1281    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
1282    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
1283    /// `x` and `y` point into the same allocated object.
1284    ///
1285    /// Compared to [`sub`], this method basically delays the requirement of staying within the
1286    /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
1287    /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
1288    /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
1289    /// can be optimized better and is thus preferable in performance-sensitive code.
1290    ///
1291    /// The delayed check only considers the value of the pointer that was dereferenced, not the
1292    /// intermediate values used during the computation of the final result. For example,
1293    /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
1294    /// allocated object and then re-entering it later is permitted.
1295    ///
1296    /// [`sub`]: #method.sub
1297    /// [allocated object]: crate::ptr#allocated-object
1298    ///
1299    /// # Examples
1300    ///
1301    /// ```
1302    /// // Iterate using a raw pointer in increments of two elements (backwards)
1303    /// let data = [1u8, 2, 3, 4, 5];
1304    /// let mut ptr: *const u8 = data.as_ptr();
1305    /// let start_rounded_down = ptr.wrapping_sub(2);
1306    /// ptr = ptr.wrapping_add(4);
1307    /// let step = 2;
1308    /// // This loop prints "5, 3, 1, "
1309    /// while ptr != start_rounded_down {
1310    ///     unsafe {
1311    ///         print!("{}, ", *ptr);
1312    ///     }
1313    ///     ptr = ptr.wrapping_sub(step);
1314    /// }
1315    /// ```
1316    #[stable(feature = "pointer_methods", since = "1.26.0")]
1317    #[must_use = "returns a new pointer rather than modifying its argument"]
1318    #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
1319    #[inline(always)]
1320    pub const fn wrapping_sub(self, count: usize) -> Self
1321    where
1322        T: Sized,
1323    {
1324        self.wrapping_offset((count as isize).wrapping_neg())
1325    }
1326
1327    /// Subtracts an unsigned offset in bytes from a pointer using wrapping arithmetic.
1328    ///
1329    /// `count` is in units of bytes.
1330    ///
1331    /// This is purely a convenience for casting to a `u8` pointer and
1332    /// using [wrapping_sub][pointer::wrapping_sub] on it. See that method for documentation.
1333    ///
1334    /// For non-`Sized` pointees this operation changes only the data pointer,
1335    /// leaving the metadata untouched.
1336    #[must_use]
1337    #[inline(always)]
1338    #[stable(feature = "pointer_byte_offsets", since = "1.75.0")]
1339    #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")]
1340    pub const fn wrapping_byte_sub(self, count: usize) -> Self {
1341        self.cast::<u8>().wrapping_sub(count).with_metadata_of(self)
1342    }
1343
1344    /// Reads the value from `self` without moving it. This leaves the
1345    /// memory in `self` unchanged.
1346    ///
1347    /// See [`ptr::read`] for safety concerns and examples.
1348    ///
1349    /// [`ptr::read`]: crate::ptr::read()
1350    #[stable(feature = "pointer_methods", since = "1.26.0")]
1351    #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
1352    #[inline(always)]
1353    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1354    pub const unsafe fn read(self) -> T
1355    where
1356        T: Sized,
1357    {
1358        // SAFETY: the caller must uphold the safety contract for ``.
1359        unsafe { read(self) }
1360    }
1361
1362    /// Performs a volatile read of the value from `self` without moving it. This
1363    /// leaves the memory in `self` unchanged.
1364    ///
1365    /// Volatile operations are intended to act on I/O memory, and are guaranteed
1366    /// to not be elided or reordered by the compiler across other volatile
1367    /// operations.
1368    ///
1369    /// See [`ptr::read_volatile`] for safety concerns and examples.
1370    ///
1371    /// [`ptr::read_volatile`]: crate::ptr::read_volatile()
1372    #[stable(feature = "pointer_methods", since = "1.26.0")]
1373    #[inline(always)]
1374    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1375    pub unsafe fn read_volatile(self) -> T
1376    where
1377        T: Sized,
1378    {
1379        // SAFETY: the caller must uphold the safety contract for `read_volatile`.
1380        unsafe { read_volatile(self) }
1381    }
1382
1383    /// Reads the value from `self` without moving it. This leaves the
1384    /// memory in `self` unchanged.
1385    ///
1386    /// Unlike `read`, the pointer may be unaligned.
1387    ///
1388    /// See [`ptr::read_unaligned`] for safety concerns and examples.
1389    ///
1390    /// [`ptr::read_unaligned`]: crate::ptr::read_unaligned()
1391    #[stable(feature = "pointer_methods", since = "1.26.0")]
1392    #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
1393    #[inline(always)]
1394    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1395    pub const unsafe fn read_unaligned(self) -> T
1396    where
1397        T: Sized,
1398    {
1399        // SAFETY: the caller must uphold the safety contract for `read_unaligned`.
1400        unsafe { read_unaligned(self) }
1401    }
1402
1403    /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
1404    /// and destination may overlap.
1405    ///
1406    /// NOTE: this has the *same* argument order as [`ptr::copy`].
1407    ///
1408    /// See [`ptr::copy`] for safety concerns and examples.
1409    ///
1410    /// [`ptr::copy`]: crate::ptr::copy()
1411    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1412    #[stable(feature = "pointer_methods", since = "1.26.0")]
1413    #[inline(always)]
1414    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1415    pub const unsafe fn copy_to(self, dest: *mut T, count: usize)
1416    where
1417        T: Sized,
1418    {
1419        // SAFETY: the caller must uphold the safety contract for `copy`.
1420        unsafe { copy(self, dest, count) }
1421    }
1422
1423    /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source
1424    /// and destination may *not* overlap.
1425    ///
1426    /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`].
1427    ///
1428    /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
1429    ///
1430    /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
1431    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1432    #[stable(feature = "pointer_methods", since = "1.26.0")]
1433    #[inline(always)]
1434    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1435    pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize)
1436    where
1437        T: Sized,
1438    {
1439        // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
1440        unsafe { copy_nonoverlapping(self, dest, count) }
1441    }
1442
1443    /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
1444    /// and destination may overlap.
1445    ///
1446    /// NOTE: this has the *opposite* argument order of [`ptr::copy`].
1447    ///
1448    /// See [`ptr::copy`] for safety concerns and examples.
1449    ///
1450    /// [`ptr::copy`]: crate::ptr::copy()
1451    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1452    #[stable(feature = "pointer_methods", since = "1.26.0")]
1453    #[inline(always)]
1454    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1455    pub const unsafe fn copy_from(self, src: *const T, count: usize)
1456    where
1457        T: Sized,
1458    {
1459        // SAFETY: the caller must uphold the safety contract for `copy`.
1460        unsafe { copy(src, self, count) }
1461    }
1462
1463    /// Copies `count * size_of<T>` bytes from `src` to `self`. The source
1464    /// and destination may *not* overlap.
1465    ///
1466    /// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`].
1467    ///
1468    /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
1469    ///
1470    /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
1471    #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.83.0")]
1472    #[stable(feature = "pointer_methods", since = "1.26.0")]
1473    #[inline(always)]
1474    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1475    pub const unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize)
1476    where
1477        T: Sized,
1478    {
1479        // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`.
1480        unsafe { copy_nonoverlapping(src, self, count) }
1481    }
1482
1483    /// Executes the destructor (if any) of the pointed-to value.
1484    ///
1485    /// See [`ptr::drop_in_place`] for safety concerns and examples.
1486    ///
1487    /// [`ptr::drop_in_place`]: crate::ptr::drop_in_place()
1488    #[stable(feature = "pointer_methods", since = "1.26.0")]
1489    #[inline(always)]
1490    pub unsafe fn drop_in_place(self) {
1491        // SAFETY: the caller must uphold the safety contract for `drop_in_place`.
1492        unsafe { drop_in_place(self) }
1493    }
1494
1495    /// Overwrites a memory location with the given value without reading or
1496    /// dropping the old value.
1497    ///
1498    /// See [`ptr::write`] for safety concerns and examples.
1499    ///
1500    /// [`ptr::write`]: crate::ptr::write()
1501    #[stable(feature = "pointer_methods", since = "1.26.0")]
1502    #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
1503    #[inline(always)]
1504    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1505    pub const unsafe fn write(self, val: T)
1506    where
1507        T: Sized,
1508    {
1509        // SAFETY: the caller must uphold the safety contract for `write`.
1510        unsafe { write(self, val) }
1511    }
1512
1513    /// Invokes memset on the specified pointer, setting `count * size_of::<T>()`
1514    /// bytes of memory starting at `self` to `val`.
1515    ///
1516    /// See [`ptr::write_bytes`] for safety concerns and examples.
1517    ///
1518    /// [`ptr::write_bytes`]: crate::ptr::write_bytes()
1519    #[doc(alias = "memset")]
1520    #[stable(feature = "pointer_methods", since = "1.26.0")]
1521    #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
1522    #[inline(always)]
1523    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1524    pub const unsafe fn write_bytes(self, val: u8, count: usize)
1525    where
1526        T: Sized,
1527    {
1528        // SAFETY: the caller must uphold the safety contract for `write_bytes`.
1529        unsafe { write_bytes(self, val, count) }
1530    }
1531
1532    /// Performs a volatile write of a memory location with the given value without
1533    /// reading or dropping the old value.
1534    ///
1535    /// Volatile operations are intended to act on I/O memory, and are guaranteed
1536    /// to not be elided or reordered by the compiler across other volatile
1537    /// operations.
1538    ///
1539    /// See [`ptr::write_volatile`] for safety concerns and examples.
1540    ///
1541    /// [`ptr::write_volatile`]: crate::ptr::write_volatile()
1542    #[stable(feature = "pointer_methods", since = "1.26.0")]
1543    #[inline(always)]
1544    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1545    pub unsafe fn write_volatile(self, val: T)
1546    where
1547        T: Sized,
1548    {
1549        // SAFETY: the caller must uphold the safety contract for `write_volatile`.
1550        unsafe { write_volatile(self, val) }
1551    }
1552
1553    /// Overwrites a memory location with the given value without reading or
1554    /// dropping the old value.
1555    ///
1556    /// Unlike `write`, the pointer may be unaligned.
1557    ///
1558    /// See [`ptr::write_unaligned`] for safety concerns and examples.
1559    ///
1560    /// [`ptr::write_unaligned`]: crate::ptr::write_unaligned()
1561    #[stable(feature = "pointer_methods", since = "1.26.0")]
1562    #[rustc_const_stable(feature = "const_ptr_write", since = "1.83.0")]
1563    #[inline(always)]
1564    #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
1565    pub const unsafe fn write_unaligned(self, val: T)
1566    where
1567        T: Sized,
1568    {
1569        // SAFETY: the caller must uphold the safety contract for `write_unaligned`.
1570        unsafe { write_unaligned(self, val) }
1571    }
1572
1573    /// Replaces the value at `self` with `src`, returning the old
1574    /// value, without dropping either.
1575    ///
1576    /// See [`ptr::replace`] for safety concerns and examples.
1577    ///
1578    /// [`ptr::replace`]: crate::ptr::replace()
1579    #[stable(feature = "pointer_methods", since = "1.26.0")]
1580    #[inline(always)]
1581    pub unsafe fn replace(self, src: T) -> T
1582    where
1583        T: Sized,
1584    {
1585        // SAFETY: the caller must uphold the safety contract for `replace`.
1586        unsafe { replace(self, src) }
1587    }
1588
1589    /// Swaps the values at two mutable locations of the same type, without
1590    /// deinitializing either. They may overlap, unlike `mem::swap` which is
1591    /// otherwise equivalent.
1592    ///
1593    /// See [`ptr::swap`] for safety concerns and examples.
1594    ///
1595    /// [`ptr::swap`]: crate::ptr::swap()
1596    #[stable(feature = "pointer_methods", since = "1.26.0")]
1597    #[rustc_const_stable(feature = "const_swap", since = "1.85.0")]
1598    #[inline(always)]
1599    pub const unsafe fn swap(self, with: *mut T)
1600    where
1601        T: Sized,
1602    {
1603        // SAFETY: the caller must uphold the safety contract for `swap`.
1604        unsafe { swap(self, with) }
1605    }
1606
1607    /// Computes the offset that needs to be applied to the pointer in order to make it aligned to
1608    /// `align`.
1609    ///
1610    /// If it is not possible to align the pointer, the implementation returns
1611    /// `usize::MAX`.
1612    ///
1613    /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be
1614    /// used with the `wrapping_add` method.
1615    ///
1616    /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go
1617    /// beyond the allocation that the pointer points into. It is up to the caller to ensure that
1618    /// the returned offset is correct in all terms other than alignment.
1619    ///
1620    /// # Panics
1621    ///
1622    /// The function panics if `align` is not a power-of-two.
1623    ///
1624    /// # Examples
1625    ///
1626    /// Accessing adjacent `u8` as `u16`
1627    ///
1628    /// ```
1629    /// use std::mem::align_of;
1630    ///
1631    /// # unsafe {
1632    /// let mut x = [5_u8, 6, 7, 8, 9];
1633    /// let ptr = x.as_mut_ptr();
1634    /// let offset = ptr.align_offset(align_of::<u16>());
1635    ///
1636    /// if offset < x.len() - 1 {
1637    ///     let u16_ptr = ptr.add(offset).cast::<u16>();
1638    ///     *u16_ptr = 0;
1639    ///
1640    ///     assert!(x == [0, 0, 7, 8, 9] || x == [5, 0, 0, 8, 9]);
1641    /// } else {
1642    ///     // while the pointer can be aligned via `offset`, it would point
1643    ///     // outside the allocation
1644    /// }
1645    /// # }
1646    /// ```
1647    #[must_use]
1648    #[inline]
1649    #[stable(feature = "align_offset", since = "1.36.0")]
1650    pub fn align_offset(self, align: usize) -> usize
1651    where
1652        T: Sized,
1653    {
1654        if !align.is_power_of_two() {
1655            panic!("align_offset: align is not a power-of-two");
1656        }
1657
1658        // SAFETY: `align` has been checked to be a power of 2 above
1659        let ret = unsafe { align_offset(self, align) };
1660
1661        // Inform Miri that we want to consider the resulting pointer to be suitably aligned.
1662        #[cfg(miri)]
1663        if ret != usize::MAX {
1664            intrinsics::miri_promise_symbolic_alignment(
1665                self.wrapping_add(ret).cast_const().cast(),
1666                align,
1667            );
1668        }
1669
1670        ret
1671    }
1672
1673    /// Returns whether the pointer is properly aligned for `T`.
1674    ///
1675    /// # Examples
1676    ///
1677    /// ```
1678    /// // On some platforms, the alignment of i32 is less than 4.
1679    /// #[repr(align(4))]
1680    /// struct AlignedI32(i32);
1681    ///
1682    /// let mut data = AlignedI32(42);
1683    /// let ptr = &mut data as *mut AlignedI32;
1684    ///
1685    /// assert!(ptr.is_aligned());
1686    /// assert!(!ptr.wrapping_byte_add(1).is_aligned());
1687    /// ```
1688    #[must_use]
1689    #[inline]
1690    #[stable(feature = "pointer_is_aligned", since = "1.79.0")]
1691    pub fn is_aligned(self) -> bool
1692    where
1693        T: Sized,
1694    {
1695        self.is_aligned_to(mem::align_of::<T>())
1696    }
1697
1698    /// Returns whether the pointer is aligned to `align`.
1699    ///
1700    /// For non-`Sized` pointees this operation considers only the data pointer,
1701    /// ignoring the metadata.
1702    ///
1703    /// # Panics
1704    ///
1705    /// The function panics if `align` is not a power-of-two (this includes 0).
1706    ///
1707    /// # Examples
1708    ///
1709    /// ```
1710    /// #![feature(pointer_is_aligned_to)]
1711    ///
1712    /// // On some platforms, the alignment of i32 is less than 4.
1713    /// #[repr(align(4))]
1714    /// struct AlignedI32(i32);
1715    ///
1716    /// let mut data = AlignedI32(42);
1717    /// let ptr = &mut data as *mut AlignedI32;
1718    ///
1719    /// assert!(ptr.is_aligned_to(1));
1720    /// assert!(ptr.is_aligned_to(2));
1721    /// assert!(ptr.is_aligned_to(4));
1722    ///
1723    /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
1724    /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
1725    ///
1726    /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
1727    /// ```
1728    #[must_use]
1729    #[inline]
1730    #[unstable(feature = "pointer_is_aligned_to", issue = "96284")]
1731    pub fn is_aligned_to(self, align: usize) -> bool {
1732        if !align.is_power_of_two() {
1733            panic!("is_aligned_to: align is not a power-of-two");
1734        }
1735
1736        self.addr() & (align - 1) == 0
1737    }
1738}
1739
1740impl<T> *mut [T] {
1741    /// Returns the length of a raw slice.
1742    ///
1743    /// The returned value is the number of **elements**, not the number of bytes.
1744    ///
1745    /// This function is safe, even when the raw slice cannot be cast to a slice
1746    /// reference because the pointer is null or unaligned.
1747    ///
1748    /// # Examples
1749    ///
1750    /// ```rust
1751    /// use std::ptr;
1752    ///
1753    /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1754    /// assert_eq!(slice.len(), 3);
1755    /// ```
1756    #[inline(always)]
1757    #[stable(feature = "slice_ptr_len", since = "1.79.0")]
1758    #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")]
1759    pub const fn len(self) -> usize {
1760        metadata(self)
1761    }
1762
1763    /// Returns `true` if the raw slice has a length of 0.
1764    ///
1765    /// # Examples
1766    ///
1767    /// ```
1768    /// use std::ptr;
1769    ///
1770    /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1771    /// assert!(!slice.is_empty());
1772    /// ```
1773    #[inline(always)]
1774    #[stable(feature = "slice_ptr_len", since = "1.79.0")]
1775    #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")]
1776    pub const fn is_empty(self) -> bool {
1777        self.len() == 0
1778    }
1779
1780    /// Gets a raw, mutable pointer to the underlying array.
1781    ///
1782    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
1783    #[unstable(feature = "slice_as_array", issue = "133508")]
1784    #[inline]
1785    #[must_use]
1786    pub const fn as_mut_array<const N: usize>(self) -> Option<*mut [T; N]> {
1787        if self.len() == N {
1788            let me = self.as_mut_ptr() as *mut [T; N];
1789            Some(me)
1790        } else {
1791            None
1792        }
1793    }
1794
1795    /// Divides one mutable raw slice into two at an index.
1796    ///
1797    /// The first will contain all indices from `[0, mid)` (excluding
1798    /// the index `mid` itself) and the second will contain all
1799    /// indices from `[mid, len)` (excluding the index `len` itself).
1800    ///
1801    /// # Panics
1802    ///
1803    /// Panics if `mid > len`.
1804    ///
1805    /// # Safety
1806    ///
1807    /// `mid` must be [in-bounds] of the underlying [allocated object].
1808    /// Which means `self` must be dereferenceable and span a single allocation
1809    /// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
1810    /// requirements is *[undefined behavior]* even if the resulting pointers are not used.
1811    ///
1812    /// Since `len` being in-bounds it is not a safety invariant of `*mut [T]` the
1813    /// safety requirements of this method are the same as for [`split_at_mut_unchecked`].
1814    /// The explicit bounds check is only as useful as `len` is correct.
1815    ///
1816    /// [`split_at_mut_unchecked`]: #method.split_at_mut_unchecked
1817    /// [in-bounds]: #method.add
1818    /// [allocated object]: crate::ptr#allocated-object
1819    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1820    ///
1821    /// # Examples
1822    ///
1823    /// ```
1824    /// #![feature(raw_slice_split)]
1825    /// #![feature(slice_ptr_get)]
1826    ///
1827    /// let mut v = [1, 0, 3, 0, 5, 6];
1828    /// let ptr = &mut v as *mut [_];
1829    /// unsafe {
1830    ///     let (left, right) = ptr.split_at_mut(2);
1831    ///     assert_eq!(&*left, [1, 0]);
1832    ///     assert_eq!(&*right, [3, 0, 5, 6]);
1833    /// }
1834    /// ```
1835    #[inline(always)]
1836    #[track_caller]
1837    #[unstable(feature = "raw_slice_split", issue = "95595")]
1838    pub unsafe fn split_at_mut(self, mid: usize) -> (*mut [T], *mut [T]) {
1839        assert!(mid <= self.len());
1840        // SAFETY: The assert above is only a safety-net as long as `self.len()` is correct
1841        // The actual safety requirements of this function are the same as for `split_at_mut_unchecked`
1842        unsafe { self.split_at_mut_unchecked(mid) }
1843    }
1844
1845    /// Divides one mutable raw slice into two at an index, without doing bounds checking.
1846    ///
1847    /// The first will contain all indices from `[0, mid)` (excluding
1848    /// the index `mid` itself) and the second will contain all
1849    /// indices from `[mid, len)` (excluding the index `len` itself).
1850    ///
1851    /// # Safety
1852    ///
1853    /// `mid` must be [in-bounds] of the underlying [allocated object].
1854    /// Which means `self` must be dereferenceable and span a single allocation
1855    /// that is at least `mid * size_of::<T>()` bytes long. Not upholding these
1856    /// requirements is *[undefined behavior]* even if the resulting pointers are not used.
1857    ///
1858    /// [in-bounds]: #method.add
1859    /// [out-of-bounds index]: #method.add
1860    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1861    ///
1862    /// # Examples
1863    ///
1864    /// ```
1865    /// #![feature(raw_slice_split)]
1866    ///
1867    /// let mut v = [1, 0, 3, 0, 5, 6];
1868    /// // scoped to restrict the lifetime of the borrows
1869    /// unsafe {
1870    ///     let ptr = &mut v as *mut [_];
1871    ///     let (left, right) = ptr.split_at_mut_unchecked(2);
1872    ///     assert_eq!(&*left, [1, 0]);
1873    ///     assert_eq!(&*right, [3, 0, 5, 6]);
1874    ///     (&mut *left)[1] = 2;
1875    ///     (&mut *right)[1] = 4;
1876    /// }
1877    /// assert_eq!(v, [1, 2, 3, 4, 5, 6]);
1878    /// ```
1879    #[inline(always)]
1880    #[unstable(feature = "raw_slice_split", issue = "95595")]
1881    pub unsafe fn split_at_mut_unchecked(self, mid: usize) -> (*mut [T], *mut [T]) {
1882        let len = self.len();
1883        let ptr = self.as_mut_ptr();
1884
1885        // SAFETY: Caller must pass a valid pointer and an index that is in-bounds.
1886        let tail = unsafe { ptr.add(mid) };
1887        (
1888            crate::ptr::slice_from_raw_parts_mut(ptr, mid),
1889            crate::ptr::slice_from_raw_parts_mut(tail, len - mid),
1890        )
1891    }
1892
1893    /// Returns a raw pointer to the slice's buffer.
1894    ///
1895    /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
1896    ///
1897    /// # Examples
1898    ///
1899    /// ```rust
1900    /// #![feature(slice_ptr_get)]
1901    /// use std::ptr;
1902    ///
1903    /// let slice: *mut [i8] = ptr::slice_from_raw_parts_mut(ptr::null_mut(), 3);
1904    /// assert_eq!(slice.as_mut_ptr(), ptr::null_mut());
1905    /// ```
1906    #[inline(always)]
1907    #[unstable(feature = "slice_ptr_get", issue = "74265")]
1908    pub const fn as_mut_ptr(self) -> *mut T {
1909        self as *mut T
1910    }
1911
1912    /// Returns a raw pointer to an element or subslice, without doing bounds
1913    /// checking.
1914    ///
1915    /// Calling this method with an [out-of-bounds index] or when `self` is not dereferenceable
1916    /// is *[undefined behavior]* even if the resulting pointer is not used.
1917    ///
1918    /// [out-of-bounds index]: #method.add
1919    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1920    ///
1921    /// # Examples
1922    ///
1923    /// ```
1924    /// #![feature(slice_ptr_get)]
1925    ///
1926    /// let x = &mut [1, 2, 4] as *mut [i32];
1927    ///
1928    /// unsafe {
1929    ///     assert_eq!(x.get_unchecked_mut(1), x.as_mut_ptr().add(1));
1930    /// }
1931    /// ```
1932    #[unstable(feature = "slice_ptr_get", issue = "74265")]
1933    #[inline(always)]
1934    pub unsafe fn get_unchecked_mut<I>(self, index: I) -> *mut I::Output
1935    where
1936        I: SliceIndex<[T]>,
1937    {
1938        // SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds.
1939        unsafe { index.get_unchecked_mut(self) }
1940    }
1941
1942    /// Returns `None` if the pointer is null, or else returns a shared slice to
1943    /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
1944    /// that the value has to be initialized.
1945    ///
1946    /// For the mutable counterpart see [`as_uninit_slice_mut`].
1947    ///
1948    /// [`as_ref`]: pointer#method.as_ref-1
1949    /// [`as_uninit_slice_mut`]: #method.as_uninit_slice_mut
1950    ///
1951    /// # Safety
1952    ///
1953    /// When calling this method, you have to ensure that *either* the pointer is null *or*
1954    /// all of the following is true:
1955    ///
1956    /// * The pointer must be [valid] for reads for `ptr.len() * mem::size_of::<T>()` many bytes,
1957    ///   and it must be properly aligned. This means in particular:
1958    ///
1959    ///     * The entire memory range of this slice must be contained within a single [allocated object]!
1960    ///       Slices can never span across multiple allocated objects.
1961    ///
1962    ///     * The pointer must be aligned even for zero-length slices. One
1963    ///       reason for this is that enum layout optimizations may rely on references
1964    ///       (including slices of any length) being aligned and non-null to distinguish
1965    ///       them from other data. You can obtain a pointer that is usable as `data`
1966    ///       for zero-length slices using [`NonNull::dangling()`].
1967    ///
1968    /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
1969    ///   See the safety documentation of [`pointer::offset`].
1970    ///
1971    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
1972    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
1973    ///   In particular, while this reference exists, the memory the pointer points to must
1974    ///   not get mutated (except inside `UnsafeCell`).
1975    ///
1976    /// This applies even if the result of this method is unused!
1977    ///
1978    /// See also [`slice::from_raw_parts`][].
1979    ///
1980    /// [valid]: crate::ptr#safety
1981    /// [allocated object]: crate::ptr#allocated-object
1982    ///
1983    /// # Panics during const evaluation
1984    ///
1985    /// This method will panic during const evaluation if the pointer cannot be
1986    /// determined to be null or not. See [`is_null`] for more information.
1987    ///
1988    /// [`is_null`]: #method.is_null-1
1989    #[inline]
1990    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
1991    pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> {
1992        if self.is_null() {
1993            None
1994        } else {
1995            // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`.
1996            Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) })
1997        }
1998    }
1999
2000    /// Returns `None` if the pointer is null, or else returns a unique slice to
2001    /// the value wrapped in `Some`. In contrast to [`as_mut`], this does not require
2002    /// that the value has to be initialized.
2003    ///
2004    /// For the shared counterpart see [`as_uninit_slice`].
2005    ///
2006    /// [`as_mut`]: #method.as_mut
2007    /// [`as_uninit_slice`]: #method.as_uninit_slice-1
2008    ///
2009    /// # Safety
2010    ///
2011    /// When calling this method, you have to ensure that *either* the pointer is null *or*
2012    /// all of the following is true:
2013    ///
2014    /// * The pointer must be [valid] for reads and writes for `ptr.len() * mem::size_of::<T>()`
2015    ///   many bytes, and it must be properly aligned. This means in particular:
2016    ///
2017    ///     * The entire memory range of this slice must be contained within a single [allocated object]!
2018    ///       Slices can never span across multiple allocated objects.
2019    ///
2020    ///     * The pointer must be aligned even for zero-length slices. One
2021    ///       reason for this is that enum layout optimizations may rely on references
2022    ///       (including slices of any length) being aligned and non-null to distinguish
2023    ///       them from other data. You can obtain a pointer that is usable as `data`
2024    ///       for zero-length slices using [`NonNull::dangling()`].
2025    ///
2026    /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`.
2027    ///   See the safety documentation of [`pointer::offset`].
2028    ///
2029    /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
2030    ///   arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
2031    ///   In particular, while this reference exists, the memory the pointer points to must
2032    ///   not get accessed (read or written) through any other pointer.
2033    ///
2034    /// This applies even if the result of this method is unused!
2035    ///
2036    /// See also [`slice::from_raw_parts_mut`][].
2037    ///
2038    /// [valid]: crate::ptr#safety
2039    /// [allocated object]: crate::ptr#allocated-object
2040    ///
2041    /// # Panics during const evaluation
2042    ///
2043    /// This method will panic during const evaluation if the pointer cannot be
2044    /// determined to be null or not. See [`is_null`] for more information.
2045    ///
2046    /// [`is_null`]: #method.is_null-1
2047    #[inline]
2048    #[unstable(feature = "ptr_as_uninit", issue = "75402")]
2049    pub const unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]> {
2050        if self.is_null() {
2051            None
2052        } else {
2053            // SAFETY: the caller must uphold the safety contract for `as_uninit_slice_mut`.
2054            Some(unsafe { slice::from_raw_parts_mut(self as *mut MaybeUninit<T>, self.len()) })
2055        }
2056    }
2057}
2058
2059impl<T, const N: usize> *mut [T; N] {
2060    /// Returns a raw pointer to the array's buffer.
2061    ///
2062    /// This is equivalent to casting `self` to `*mut T`, but more type-safe.
2063    ///
2064    /// # Examples
2065    ///
2066    /// ```rust
2067    /// #![feature(array_ptr_get)]
2068    /// use std::ptr;
2069    ///
2070    /// let arr: *mut [i8; 3] = ptr::null_mut();
2071    /// assert_eq!(arr.as_mut_ptr(), ptr::null_mut());
2072    /// ```
2073    #[inline]
2074    #[unstable(feature = "array_ptr_get", issue = "119834")]
2075    pub const fn as_mut_ptr(self) -> *mut T {
2076        self as *mut T
2077    }
2078
2079    /// Returns a raw pointer to a mutable slice containing the entire array.
2080    ///
2081    /// # Examples
2082    ///
2083    /// ```
2084    /// #![feature(array_ptr_get)]
2085    ///
2086    /// let mut arr = [1, 2, 5];
2087    /// let ptr: *mut [i32; 3] = &mut arr;
2088    /// unsafe {
2089    ///     (&mut *ptr.as_mut_slice())[..2].copy_from_slice(&[3, 4]);
2090    /// }
2091    /// assert_eq!(arr, [3, 4, 5]);
2092    /// ```
2093    #[inline]
2094    #[unstable(feature = "array_ptr_get", issue = "119834")]
2095    pub const fn as_mut_slice(self) -> *mut [T] {
2096        self
2097    }
2098}
2099
2100/// Pointer equality is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
2101#[stable(feature = "rust1", since = "1.0.0")]
2102impl<T: ?Sized> PartialEq for *mut T {
2103    #[inline(always)]
2104    #[allow(ambiguous_wide_pointer_comparisons)]
2105    fn eq(&self, other: &*mut T) -> bool {
2106        *self == *other
2107    }
2108}
2109
2110/// Pointer equality is an equivalence relation.
2111#[stable(feature = "rust1", since = "1.0.0")]
2112impl<T: ?Sized> Eq for *mut T {}
2113
2114/// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
2115#[stable(feature = "rust1", since = "1.0.0")]
2116impl<T: ?Sized> Ord for *mut T {
2117    #[inline]
2118    #[allow(ambiguous_wide_pointer_comparisons)]
2119    fn cmp(&self, other: &*mut T) -> Ordering {
2120        if self < other {
2121            Less
2122        } else if self == other {
2123            Equal
2124        } else {
2125            Greater
2126        }
2127    }
2128}
2129
2130/// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
2131#[stable(feature = "rust1", since = "1.0.0")]
2132impl<T: ?Sized> PartialOrd for *mut T {
2133    #[inline(always)]
2134    #[allow(ambiguous_wide_pointer_comparisons)]
2135    fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
2136        Some(self.cmp(other))
2137    }
2138
2139    #[inline(always)]
2140    #[allow(ambiguous_wide_pointer_comparisons)]
2141    fn lt(&self, other: &*mut T) -> bool {
2142        *self < *other
2143    }
2144
2145    #[inline(always)]
2146    #[allow(ambiguous_wide_pointer_comparisons)]
2147    fn le(&self, other: &*mut T) -> bool {
2148        *self <= *other
2149    }
2150
2151    #[inline(always)]
2152    #[allow(ambiguous_wide_pointer_comparisons)]
2153    fn gt(&self, other: &*mut T) -> bool {
2154        *self > *other
2155    }
2156
2157    #[inline(always)]
2158    #[allow(ambiguous_wide_pointer_comparisons)]
2159    fn ge(&self, other: &*mut T) -> bool {
2160        *self >= *other
2161    }
2162}