| use super::*; |
| use crate::cmp::Ordering::{Equal, Greater, Less}; |
| use crate::intrinsics::const_eval_select; |
| use crate::mem::SizedTypeProperties; |
| use crate::slice::{self, SliceIndex}; |
| |
| impl<T: ?Sized> *const T { |
| /// Returns `true` if the pointer is null. |
| /// |
| /// Note that unsized types have many possible null pointers, as only the |
| /// raw data pointer is considered, not their length, vtable, etc. |
| /// Therefore, two pointers that are null may still not compare equal to |
| /// each other. |
| /// |
| /// ## Behavior during const evaluation |
| /// |
| /// When this function is used during const evaluation, it may return `false` for pointers |
| /// that turn out to be null at runtime. Specifically, when a pointer to some memory |
| /// is offset beyond its bounds in such a way that the resulting pointer is null, |
| /// the function will still return `false`. There is no way for CTFE to know |
| /// the absolute position of that memory, so we cannot tell if the pointer is |
| /// null or not. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "Follow the rabbit"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// assert!(!ptr.is_null()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")] |
| #[rustc_diagnostic_item = "ptr_const_is_null"] |
| #[inline] |
| pub const fn is_null(self) -> bool { |
| #[inline] |
| fn runtime_impl(ptr: *const u8) -> bool { |
| ptr.addr() == 0 |
| } |
| |
| #[inline] |
| const fn const_impl(ptr: *const u8) -> bool { |
| // Compare via a cast to a thin pointer, so fat pointers are only |
| // considering their "data" part for null-ness. |
| match (ptr).guaranteed_eq(null_mut()) { |
| None => false, |
| Some(res) => res, |
| } |
| } |
| |
| #[allow(unused_unsafe)] |
| const_eval_select((self as *const u8,), const_impl, runtime_impl) |
| } |
| |
| /// Casts to a pointer of another type. |
| #[stable(feature = "ptr_cast", since = "1.38.0")] |
| #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")] |
| #[rustc_diagnostic_item = "const_ptr_cast"] |
| #[inline(always)] |
| pub const fn cast<U>(self) -> *const U { |
| self as _ |
| } |
| |
| /// Use the pointer value in a new pointer of another type. |
| /// |
| /// In case `meta` is a (fat) pointer to an unsized type, this operation |
| /// will ignore the pointer part, whereas for (thin) pointers to sized |
| /// types, this has the same effect as a simple cast. |
| /// |
| /// The resulting pointer will have provenance of `self`, i.e., for a fat |
| /// pointer, this operation is semantically the same as creating a new |
| /// fat pointer with the data pointer value of `self` but the metadata of |
| /// `meta`. |
| /// |
| /// # Examples |
| /// |
| /// This function is primarily useful for allowing byte-wise pointer |
| /// arithmetic on potentially fat pointers: |
| /// |
| /// ``` |
| /// #![feature(set_ptr_value)] |
| /// # use core::fmt::Debug; |
| /// let arr: [i32; 3] = [1, 2, 3]; |
| /// let mut ptr = arr.as_ptr() as *const dyn Debug; |
| /// let thin = ptr as *const u8; |
| /// unsafe { |
| /// ptr = thin.add(8).with_metadata_of(ptr); |
| /// # assert_eq!(*(ptr as *const i32), 3); |
| /// println!("{:?}", &*ptr); // will print "3" |
| /// } |
| /// ``` |
| #[unstable(feature = "set_ptr_value", issue = "75091")] |
| #[rustc_const_unstable(feature = "set_ptr_value", issue = "75091")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[inline] |
| pub const fn with_metadata_of<U>(self, meta: *const U) -> *const U |
| where |
| U: ?Sized, |
| { |
| from_raw_parts::<U>(self as *const (), metadata(meta)) |
| } |
| |
| /// Changes constness without changing the type. |
| /// |
| /// This is a bit safer than `as` because it wouldn't silently change the type if the code is |
| /// refactored. |
| #[stable(feature = "ptr_const_cast", since = "1.65.0")] |
| #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")] |
| #[rustc_diagnostic_item = "ptr_cast_mut"] |
| #[inline(always)] |
| pub const fn cast_mut(self) -> *mut T { |
| self as _ |
| } |
| |
| /// Casts a pointer to its raw bits. |
| /// |
| /// This is equivalent to `as usize`, but is more specific to enhance readability. |
| /// The inverse method is [`from_bits`](#method.from_bits). |
| /// |
| /// In particular, `*p as usize` and `p as usize` will both compile for |
| /// pointers to numeric types but do very different things, so using this |
| /// helps emphasize that reading the bits was intentional. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_to_from_bits)] |
| /// # #[cfg(not(miri))] { // doctest does not work with strict provenance |
| /// let array = [13, 42]; |
| /// let p0: *const i32 = &array[0]; |
| /// assert_eq!(<*const _>::from_bits(p0.to_bits()), p0); |
| /// let p1: *const i32 = &array[1]; |
| /// assert_eq!(p1.to_bits() - p0.to_bits(), 4); |
| /// # } |
| /// ``` |
| #[unstable(feature = "ptr_to_from_bits", issue = "91126")] |
| #[deprecated( |
| since = "1.67.0", |
| note = "replaced by the `expose_provenance` method, or update your code \ |
| to follow the strict provenance rules using its APIs" |
| )] |
| #[inline(always)] |
| pub fn to_bits(self) -> usize |
| where |
| T: Sized, |
| { |
| self as usize |
| } |
| |
| /// Creates a pointer from its raw bits. |
| /// |
| /// This is equivalent to `as *const T`, but is more specific to enhance readability. |
| /// The inverse method is [`to_bits`](#method.to_bits). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_to_from_bits)] |
| /// # #[cfg(not(miri))] { // doctest does not work with strict provenance |
| /// use std::ptr::NonNull; |
| /// let dangling: *const u8 = NonNull::dangling().as_ptr(); |
| /// assert_eq!(<*const u8>::from_bits(1), dangling); |
| /// # } |
| /// ``` |
| #[unstable(feature = "ptr_to_from_bits", issue = "91126")] |
| #[deprecated( |
| since = "1.67.0", |
| note = "replaced by the `ptr::with_exposed_provenance` function, or update \ |
| your code to follow the strict provenance rules using its APIs" |
| )] |
| #[allow(fuzzy_provenance_casts)] // this is an unstable and semi-deprecated cast function |
| #[inline(always)] |
| pub fn from_bits(bits: usize) -> Self |
| where |
| T: Sized, |
| { |
| bits as Self |
| } |
| |
| /// Gets the "address" portion of the pointer. |
| /// |
| /// This is similar to `self as usize`, which semantically discards *provenance* and |
| /// *address-space* information. However, unlike `self as usize`, casting the returned address |
| /// back to a pointer yields a [pointer without provenance][without_provenance], which is undefined behavior to dereference. To |
| /// properly restore the lost information and obtain a dereferenceable pointer, use |
| /// [`with_addr`][pointer::with_addr] or [`map_addr`][pointer::map_addr]. |
| /// |
| /// If using those APIs is not possible because there is no way to preserve a pointer with the |
| /// required provenance, then Strict Provenance might not be for you. Use pointer-integer casts |
| /// or [`expose_provenance`][pointer::expose_provenance] and [`with_exposed_provenance`][with_exposed_provenance] |
| /// instead. However, note that this makes your code less portable and less amenable to tools |
| /// that check for compliance with the Rust memory model. |
| /// |
| /// On most platforms this will produce a value with the same bytes as the original |
| /// pointer, because all the bytes are dedicated to describing the address. |
| /// Platforms which need to store additional information in the pointer may |
| /// perform a change of representation to produce a value containing only the address |
| /// portion of the pointer. What that means is up to the platform to define. |
| /// |
| /// This API and its claimed semantics are part of the Strict Provenance experiment, and as such |
| /// might change in the future (including possibly weakening this so it becomes wholly |
| /// equivalent to `self as usize`). See the [module documentation][crate::ptr] for details. |
| #[must_use] |
| #[inline(always)] |
| #[unstable(feature = "strict_provenance", issue = "95228")] |
| pub fn addr(self) -> usize { |
| // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic. |
| // SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the |
| // provenance). |
| unsafe { mem::transmute(self.cast::<()>()) } |
| } |
| |
| /// Exposes the "provenance" part of the pointer for future use in |
| /// [`with_exposed_provenance`][] and returns the "address" portion. |
| /// |
| /// This is equivalent to `self as usize`, which semantically discards *provenance* and |
| /// *address-space* information. Furthermore, this (like the `as` cast) has the implicit |
| /// side-effect of marking the provenance as 'exposed', so on platforms that support it you can |
| /// later call [`with_exposed_provenance`][] to reconstitute the original pointer including its |
| /// provenance. (Reconstructing address space information, if required, is your responsibility.) |
| /// |
| /// Using this method means that code is *not* following [Strict |
| /// Provenance][super#strict-provenance] rules. Supporting |
| /// [`with_exposed_provenance`][] complicates specification and reasoning and may not be supported by |
| /// tools that help you to stay conformant with the Rust memory model, so it is recommended to |
| /// use [`addr`][pointer::addr] wherever possible. |
| /// |
| /// On most platforms this will produce a value with the same bytes as the original pointer, |
| /// because all the bytes are dedicated to describing the address. Platforms which need to store |
| /// additional information in the pointer may not support this operation, since the 'expose' |
| /// side-effect which is required for [`with_exposed_provenance`][] to work is typically not |
| /// available. |
| /// |
| /// It is unclear whether this method can be given a satisfying unambiguous specification. This |
| /// API and its claimed semantics are part of [Exposed Provenance][super#exposed-provenance]. |
| /// |
| /// [`with_exposed_provenance`]: with_exposed_provenance |
| #[must_use] |
| #[inline(always)] |
| #[unstable(feature = "exposed_provenance", issue = "95228")] |
| pub fn expose_provenance(self) -> usize { |
| // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic. |
| self.cast::<()>() as usize |
| } |
| |
| /// Creates a new pointer with the given address. |
| /// |
| /// This performs the same operation as an `addr as ptr` cast, but copies |
| /// the *address-space* and *provenance* of `self` to the new pointer. |
| /// This allows us to dynamically preserve and propagate this important |
| /// information in a way that is otherwise impossible with a unary cast. |
| /// |
| /// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset |
| /// `self` to the given address, and therefore has all the same capabilities and restrictions. |
| /// |
| /// This API and its claimed semantics are part of the Strict Provenance experiment, |
| /// see the [module documentation][crate::ptr] for details. |
| #[must_use] |
| #[inline] |
| #[unstable(feature = "strict_provenance", issue = "95228")] |
| pub fn with_addr(self, addr: usize) -> Self { |
| // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic. |
| // |
| // In the mean-time, this operation is defined to be "as if" it was |
| // a wrapping_offset, so we can emulate it as such. This should properly |
| // restore pointer provenance even under today's compiler. |
| let self_addr = self.addr() as isize; |
| let dest_addr = addr as isize; |
| let offset = dest_addr.wrapping_sub(self_addr); |
| |
| // This is the canonical desugaring of this operation |
| self.wrapping_byte_offset(offset) |
| } |
| |
| /// Creates a new pointer by mapping `self`'s address to a new one. |
| /// |
| /// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details. |
| /// |
| /// This API and its claimed semantics are part of the Strict Provenance experiment, |
| /// see the [module documentation][crate::ptr] for details. |
| #[must_use] |
| #[inline] |
| #[unstable(feature = "strict_provenance", issue = "95228")] |
| pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self { |
| self.with_addr(f(self.addr())) |
| } |
| |
| /// Decompose a (possibly wide) pointer into its data pointer and metadata components. |
| /// |
| /// The pointer can be later reconstructed with [`from_raw_parts`]. |
| #[unstable(feature = "ptr_metadata", issue = "81513")] |
| #[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")] |
| #[inline] |
| pub const fn to_raw_parts(self) -> (*const (), <T as super::Pointee>::Metadata) { |
| (self.cast(), metadata(self)) |
| } |
| |
| /// Returns `None` if the pointer is null, or else returns a shared reference to |
| /// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`] |
| /// must be used instead. |
| /// |
| /// [`as_uninit_ref`]: #method.as_uninit_ref |
| /// |
| /// # Safety |
| /// |
| /// When calling this method, you have to ensure that *either* the pointer is null *or* |
| /// all of the following is true: |
| /// |
| /// * The pointer must be properly aligned. |
| /// |
| /// * It must be "dereferenceable" in the sense defined in [the module documentation]. |
| /// |
| /// * The pointer must point to an initialized instance of `T`. |
| /// |
| /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is |
| /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. |
| /// In particular, while this reference exists, the memory the pointer points to must |
| /// not get mutated (except inside `UnsafeCell`). |
| /// |
| /// This applies even if the result of this method is unused! |
| /// (The part about being initialized is not yet fully decided, but until |
| /// it is, the only safe approach is to ensure that they are indeed initialized.) |
| /// |
| /// [the module documentation]: crate::ptr#safety |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// if let Some(val_back) = ptr.as_ref() { |
| /// println!("We got back the value: {val_back}!"); |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// # Null-unchecked version |
| /// |
| /// If you are sure the pointer can never be null and are looking for some kind of |
| /// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can |
| /// dereference the pointer directly. |
| /// |
| /// ``` |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// let val_back = &*ptr; |
| /// println!("We got back the value: {val_back}!"); |
| /// } |
| /// ``` |
| #[stable(feature = "ptr_as_ref", since = "1.9.0")] |
| #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")] |
| #[inline] |
| pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> { |
| // SAFETY: the caller must guarantee that `self` is valid |
| // for a reference if it isn't null. |
| if self.is_null() { None } else { unsafe { Some(&*self) } } |
| } |
| |
| /// Returns a shared reference to the value behind the pointer. |
| /// If the pointer may be null or the value may be uninitialized, [`as_uninit_ref`] must be used instead. |
| /// If the pointer may be null, but the value is known to have been initialized, [`as_ref`] must be used instead. |
| /// |
| /// [`as_ref`]: #method.as_ref |
| /// [`as_uninit_ref`]: #method.as_uninit_ref |
| /// |
| /// # Safety |
| /// |
| /// When calling this method, you have to ensure that all of the following is true: |
| /// |
| /// * The pointer must be properly aligned. |
| /// |
| /// * It must be "dereferenceable" in the sense defined in [the module documentation]. |
| /// |
| /// * The pointer must point to an initialized instance of `T`. |
| /// |
| /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is |
| /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. |
| /// In particular, while this reference exists, the memory the pointer points to must |
| /// not get mutated (except inside `UnsafeCell`). |
| /// |
| /// This applies even if the result of this method is unused! |
| /// (The part about being initialized is not yet fully decided, but until |
| /// it is, the only safe approach is to ensure that they are indeed initialized.) |
| /// |
| /// [the module documentation]: crate::ptr#safety |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_as_ref_unchecked)] |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// println!("We got back the value: {}!", ptr.as_ref_unchecked()); |
| /// } |
| /// ``` |
| // FIXME: mention it in the docs for `as_ref` and `as_uninit_ref` once stabilized. |
| #[unstable(feature = "ptr_as_ref_unchecked", issue = "122034")] |
| #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")] |
| #[inline] |
| #[must_use] |
| pub const unsafe fn as_ref_unchecked<'a>(self) -> &'a T { |
| // SAFETY: the caller must guarantee that `self` is valid for a reference |
| unsafe { &*self } |
| } |
| |
| /// Returns `None` if the pointer is null, or else returns a shared reference to |
| /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require |
| /// that the value has to be initialized. |
| /// |
| /// [`as_ref`]: #method.as_ref |
| /// |
| /// # Safety |
| /// |
| /// When calling this method, you have to ensure that *either* the pointer is null *or* |
| /// all of the following is true: |
| /// |
| /// * The pointer must be properly aligned. |
| /// |
| /// * It must be "dereferenceable" in the sense defined in [the module documentation]. |
| /// |
| /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is |
| /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. |
| /// In particular, while this reference exists, the memory the pointer points to must |
| /// not get mutated (except inside `UnsafeCell`). |
| /// |
| /// This applies even if the result of this method is unused! |
| /// |
| /// [the module documentation]: crate::ptr#safety |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_as_uninit)] |
| /// |
| /// let ptr: *const u8 = &10u8 as *const u8; |
| /// |
| /// unsafe { |
| /// if let Some(val_back) = ptr.as_uninit_ref() { |
| /// println!("We got back the value: {}!", val_back.assume_init()); |
| /// } |
| /// } |
| /// ``` |
| #[inline] |
| #[unstable(feature = "ptr_as_uninit", issue = "75402")] |
| #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")] |
| pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>> |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must guarantee that `self` meets all the |
| // requirements for a reference. |
| if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) } |
| } |
| |
| /// Calculates the offset from a pointer. |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// If any of the following conditions are violated, the result is Undefined |
| /// Behavior: |
| /// |
| /// * If the computed offset is non-zero, then both the starting and resulting pointer must be |
| /// either in bounds or one byte past the end of the same [allocated object]. |
| /// (If it is zero, then the function is always well-defined.) |
| /// |
| /// * The computed offset, **in bytes**, cannot overflow an `isize`. |
| /// |
| /// * The offset being in bounds cannot rely on "wrapping around" the address |
| /// space. That is, the infinite-precision sum, **in bytes** must fit in a usize. |
| /// |
| /// The compiler and standard library generally tries to ensure allocations |
| /// never reach a size where an offset is a concern. For instance, `Vec` |
| /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so |
| /// `vec.as_ptr().add(vec.len())` is always safe. |
| /// |
| /// Most platforms fundamentally can't even construct such an allocation. |
| /// For instance, no known 64-bit platform can ever serve a request |
| /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space. |
| /// However, some 32-bit and 16-bit platforms may successfully serve a request for |
| /// more than `isize::MAX` bytes with things like Physical Address |
| /// Extension. As such, memory acquired directly from allocators or memory |
| /// mapped files *may* be too large to handle with this function. |
| /// |
| /// Consider using [`wrapping_offset`] instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// [`wrapping_offset`]: #method.wrapping_offset |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "123"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// |
| /// unsafe { |
| /// println!("{}", *ptr.offset(1) as char); |
| /// println!("{}", *ptr.offset(2) as char); |
| /// } |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn offset(self, count: isize) -> *const T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| unsafe { intrinsics::offset(self, count) } |
| } |
| |
| /// Calculates the offset from a pointer in bytes. |
| /// |
| /// `count` is in units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [offset][pointer::offset] on it. See that method for documentation |
| /// and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn byte_offset(self, count: isize) -> Self { |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| unsafe { self.cast::<u8>().offset(count).with_metadata_of(self) } |
| } |
| |
| /// Calculates the offset from a pointer using wrapping arithmetic. |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// This operation itself is always safe, but using the resulting pointer is not. |
| /// |
| /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not |
| /// be used to read or write other allocated objects. |
| /// |
| /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z` |
| /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still |
| /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless |
| /// `x` and `y` point into the same allocated object. |
| /// |
| /// Compared to [`offset`], this method basically delays the requirement of staying within the |
| /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object |
| /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a |
| /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`] |
| /// can be optimized better and is thus preferable in performance-sensitive code. |
| /// |
| /// The delayed check only considers the value of the pointer that was dereferenced, not the |
| /// intermediate values used during the computation of the final result. For example, |
| /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other |
| /// words, leaving the allocated object and then re-entering it later is permitted. |
| /// |
| /// [`offset`]: #method.offset |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// // Iterate using a raw pointer in increments of two elements |
| /// let data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *const u8 = data.as_ptr(); |
| /// let step = 2; |
| /// let end_rounded_up = ptr.wrapping_offset(6); |
| /// |
| /// // This loop prints "1, 3, 5, " |
| /// while ptr != end_rounded_up { |
| /// unsafe { |
| /// print!("{}, ", *ptr); |
| /// } |
| /// ptr = ptr.wrapping_offset(step); |
| /// } |
| /// ``` |
| #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| pub const fn wrapping_offset(self, count: isize) -> *const T |
| where |
| T: Sized, |
| { |
| // SAFETY: the `arith_offset` intrinsic has no prerequisites to be called. |
| unsafe { intrinsics::arith_offset(self, count) } |
| } |
| |
| /// Calculates the offset from a pointer in bytes using wrapping arithmetic. |
| /// |
| /// `count` is in units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [wrapping_offset][pointer::wrapping_offset] on it. See that method |
| /// for documentation. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| pub const fn wrapping_byte_offset(self, count: isize) -> Self { |
| self.cast::<u8>().wrapping_offset(count).with_metadata_of(self) |
| } |
| |
| /// Masks out bits of the pointer according to a mask. |
| /// |
| /// This is convenience for `ptr.map_addr(|a| a & mask)`. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| /// |
| /// ## Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_mask, strict_provenance)] |
| /// let v = 17_u32; |
| /// let ptr: *const u32 = &v; |
| /// |
| /// // `u32` is 4 bytes aligned, |
| /// // which means that lower 2 bits are always 0. |
| /// let tag_mask = 0b11; |
| /// let ptr_mask = !tag_mask; |
| /// |
| /// // We can store something in these lower bits |
| /// let tagged_ptr = ptr.map_addr(|a| a | 0b10); |
| /// |
| /// // Get the "tag" back |
| /// let tag = tagged_ptr.addr() & tag_mask; |
| /// assert_eq!(tag, 0b10); |
| /// |
| /// // Note that `tagged_ptr` is unaligned, it's UB to read from it. |
| /// // To get original pointer `mask` can be used: |
| /// let masked_ptr = tagged_ptr.mask(ptr_mask); |
| /// assert_eq!(unsafe { *masked_ptr }, 17); |
| /// ``` |
| #[unstable(feature = "ptr_mask", issue = "98290")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[inline(always)] |
| pub fn mask(self, mask: usize) -> *const T { |
| intrinsics::ptr_mask(self.cast::<()>(), mask).with_metadata_of(self) |
| } |
| |
| /// Calculates the distance between two pointers. The returned value is in |
| /// units of T: the distance in bytes divided by `mem::size_of::<T>()`. |
| /// |
| /// This is equivalent to `(self as isize - origin as isize) / (mem::size_of::<T>() as isize)`, |
| /// except that it has a lot more opportunities for UB, in exchange for the compiler |
| /// better understanding what you are doing. |
| /// |
| /// The primary motivation of this method is for computing the `len` of an array/slice |
| /// of `T` that you are currently representing as a "start" and "end" pointer |
| /// (and "end" is "one past the end" of the array). |
| /// In that case, `end.offset_from(start)` gets you the length of the array. |
| /// |
| /// All of the following safety requirements are trivially satisfied for this usecase. |
| /// |
| /// [`offset`]: #method.offset |
| /// |
| /// # Safety |
| /// |
| /// If any of the following conditions are violated, the result is Undefined |
| /// Behavior: |
| /// |
| /// * `self` and `origin` must either |
| /// |
| /// * both be *derived from* a pointer to the same [allocated object], and the memory range between |
| /// the two pointers must be either empty or in bounds of that object. (See below for an example.) |
| /// * or both be derived from an integer literal/constant, and point to the same address. |
| /// |
| /// * The distance between the pointers, in bytes, must be an exact multiple |
| /// of the size of `T`. |
| /// |
| /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`. |
| /// |
| /// * The distance being in bounds cannot rely on "wrapping around" the address space. |
| /// |
| /// Rust types are never larger than `isize::MAX` and Rust allocations never wrap around the |
| /// address space, so two pointers within some value of any Rust type `T` will always satisfy |
| /// the last two conditions. The standard library also generally ensures that allocations |
| /// never reach a size where an offset is a concern. For instance, `Vec` and `Box` ensure they |
| /// never allocate more than `isize::MAX` bytes, so `ptr_into_vec.offset_from(vec.as_ptr())` |
| /// always satisfies the last two conditions. |
| /// |
| /// Most platforms fundamentally can't even construct such a large allocation. |
| /// For instance, no known 64-bit platform can ever serve a request |
| /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space. |
| /// However, some 32-bit and 16-bit platforms may successfully serve a request for |
| /// more than `isize::MAX` bytes with things like Physical Address |
| /// Extension. As such, memory acquired directly from allocators or memory |
| /// mapped files *may* be too large to handle with this function. |
| /// (Note that [`offset`] and [`add`] also have a similar limitation and hence cannot be used on |
| /// such large allocations either.) |
| /// |
| /// The requirement for pointers to be derived from the same allocated object is primarily |
| /// needed for `const`-compatibility: the distance between pointers into *different* allocated |
| /// objects is not known at compile-time. However, the requirement also exists at |
| /// runtime and may be exploited by optimizations. If you wish to compute the difference between |
| /// pointers that are not guaranteed to be from the same allocation, use `(self as isize - |
| /// origin as isize) / mem::size_of::<T>()`. |
| // FIXME: recommend `addr()` instead of `as usize` once that is stable. |
| /// |
| /// [`add`]: #method.add |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a Zero-Sized Type ("ZST"). |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let a = [0; 5]; |
| /// let ptr1: *const i32 = &a[1]; |
| /// let ptr2: *const i32 = &a[3]; |
| /// unsafe { |
| /// assert_eq!(ptr2.offset_from(ptr1), 2); |
| /// assert_eq!(ptr1.offset_from(ptr2), -2); |
| /// assert_eq!(ptr1.offset(2), ptr2); |
| /// assert_eq!(ptr2.offset(-2), ptr1); |
| /// } |
| /// ``` |
| /// |
| /// *Incorrect* usage: |
| /// |
| /// ```rust,no_run |
| /// let ptr1 = Box::into_raw(Box::new(0u8)) as *const u8; |
| /// let ptr2 = Box::into_raw(Box::new(1u8)) as *const u8; |
| /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize); |
| /// // Make ptr2_other an "alias" of ptr2, but derived from ptr1. |
| /// let ptr2_other = (ptr1 as *const u8).wrapping_offset(diff); |
| /// assert_eq!(ptr2 as usize, ptr2_other as usize); |
| /// // Since ptr2_other and ptr2 are derived from pointers to different objects, |
| /// // computing their offset is undefined behavior, even though |
| /// // they point to the same address! |
| /// unsafe { |
| /// let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior |
| /// } |
| /// ``` |
| #[stable(feature = "ptr_offset_from", since = "1.47.0")] |
| #[rustc_const_stable(feature = "const_ptr_offset_from", since = "1.65.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn offset_from(self, origin: *const T) -> isize |
| where |
| T: Sized, |
| { |
| let pointee_size = mem::size_of::<T>(); |
| assert!(0 < pointee_size && pointee_size <= isize::MAX as usize); |
| // SAFETY: the caller must uphold the safety contract for `ptr_offset_from`. |
| unsafe { intrinsics::ptr_offset_from(self, origin) } |
| } |
| |
| /// Calculates the distance between two pointers. The returned value is in |
| /// units of **bytes**. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [`offset_from`][pointer::offset_from] on it. See that method for |
| /// documentation and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation considers only the data pointers, |
| /// ignoring the metadata. |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn byte_offset_from<U: ?Sized>(self, origin: *const U) -> isize { |
| // SAFETY: the caller must uphold the safety contract for `offset_from`. |
| unsafe { self.cast::<u8>().offset_from(origin.cast::<u8>()) } |
| } |
| |
| /// Calculates the distance between two pointers, *where it's known that |
| /// `self` is equal to or greater than `origin`*. The returned value is in |
| /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`. |
| /// |
| /// This computes the same value that [`offset_from`](#method.offset_from) |
| /// would compute, but with the added precondition that the offset is |
| /// guaranteed to be non-negative. This method is equivalent to |
| /// `usize::try_from(self.offset_from(origin)).unwrap_unchecked()`, |
| /// but it provides slightly more information to the optimizer, which can |
| /// sometimes allow it to optimize slightly better with some backends. |
| /// |
| /// This method can be though of as recovering the `count` that was passed |
| /// to [`add`](#method.add) (or, with the parameters in the other order, |
| /// to [`sub`](#method.sub)). The following are all equivalent, assuming |
| /// that their safety preconditions are met: |
| /// ```rust |
| /// # #![feature(ptr_sub_ptr)] |
| /// # unsafe fn blah(ptr: *const i32, origin: *const i32, count: usize) -> bool { |
| /// ptr.sub_ptr(origin) == count |
| /// # && |
| /// origin.add(count) == ptr |
| /// # && |
| /// ptr.sub(count) == origin |
| /// # } |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// - The distance between the pointers must be non-negative (`self >= origin`) |
| /// |
| /// - *All* the safety conditions of [`offset_from`](#method.offset_from) |
| /// apply to this method as well; see it for the full details. |
| /// |
| /// Importantly, despite the return type of this method being able to represent |
| /// a larger offset, it's still *not permitted* to pass pointers which differ |
| /// by more than `isize::MAX` *bytes*. As such, the result of this method will |
| /// always be less than or equal to `isize::MAX as usize`. |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a Zero-Sized Type ("ZST"). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(ptr_sub_ptr)] |
| /// |
| /// let a = [0; 5]; |
| /// let ptr1: *const i32 = &a[1]; |
| /// let ptr2: *const i32 = &a[3]; |
| /// unsafe { |
| /// assert_eq!(ptr2.sub_ptr(ptr1), 2); |
| /// assert_eq!(ptr1.add(2), ptr2); |
| /// assert_eq!(ptr2.sub(2), ptr1); |
| /// assert_eq!(ptr2.sub_ptr(ptr2), 0); |
| /// } |
| /// |
| /// // This would be incorrect, as the pointers are not correctly ordered: |
| /// // ptr1.sub_ptr(ptr2) |
| /// ``` |
| #[unstable(feature = "ptr_sub_ptr", issue = "95892")] |
| #[rustc_const_unstable(feature = "const_ptr_sub_ptr", issue = "95892")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn sub_ptr(self, origin: *const T) -> usize |
| where |
| T: Sized, |
| { |
| const fn runtime_ptr_ge(this: *const (), origin: *const ()) -> bool { |
| fn runtime(this: *const (), origin: *const ()) -> bool { |
| this >= origin |
| } |
| const fn comptime(_: *const (), _: *const ()) -> bool { |
| true |
| } |
| |
| #[allow(unused_unsafe)] |
| intrinsics::const_eval_select((this, origin), comptime, runtime) |
| } |
| |
| ub_checks::assert_unsafe_precondition!( |
| check_language_ub, |
| "ptr::sub_ptr requires `self >= origin`", |
| ( |
| this: *const () = self as *const (), |
| origin: *const () = origin as *const (), |
| ) => runtime_ptr_ge(this, origin) |
| ); |
| |
| let pointee_size = mem::size_of::<T>(); |
| assert!(0 < pointee_size && pointee_size <= isize::MAX as usize); |
| // SAFETY: the caller must uphold the safety contract for `ptr_offset_from_unsigned`. |
| unsafe { intrinsics::ptr_offset_from_unsigned(self, origin) } |
| } |
| |
| /// Returns whether two pointers are guaranteed to be equal. |
| /// |
| /// At runtime this function behaves like `Some(self == other)`. |
| /// However, in some contexts (e.g., compile-time evaluation), |
| /// it is not always possible to determine equality of two pointers, so this function may |
| /// spuriously return `None` for pointers that later actually turn out to have its equality known. |
| /// But when it returns `Some`, the pointers' equality is guaranteed to be known. |
| /// |
| /// The return value may change from `Some` to `None` and vice versa depending on the compiler |
| /// version and unsafe code must not |
| /// rely on the result of this function for soundness. It is suggested to only use this function |
| /// for performance optimizations where spurious `None` return values by this function do not |
| /// affect the outcome, but just the performance. |
| /// The consequences of using this method to make runtime and compile-time code behave |
| /// differently have not been explored. This method should not be used to introduce such |
| /// differences, and it should also not be stabilized before we have a better understanding |
| /// of this issue. |
| #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[inline] |
| pub const fn guaranteed_eq(self, other: *const T) -> Option<bool> |
| where |
| T: Sized, |
| { |
| match intrinsics::ptr_guaranteed_cmp(self, other) { |
| 2 => None, |
| other => Some(other == 1), |
| } |
| } |
| |
| /// Returns whether two pointers are guaranteed to be inequal. |
| /// |
| /// At runtime this function behaves like `Some(self != other)`. |
| /// However, in some contexts (e.g., compile-time evaluation), |
| /// it is not always possible to determine inequality of two pointers, so this function may |
| /// spuriously return `None` for pointers that later actually turn out to have its inequality known. |
| /// But when it returns `Some`, the pointers' inequality is guaranteed to be known. |
| /// |
| /// The return value may change from `Some` to `None` and vice versa depending on the compiler |
| /// version and unsafe code must not |
| /// rely on the result of this function for soundness. It is suggested to only use this function |
| /// for performance optimizations where spurious `None` return values by this function do not |
| /// affect the outcome, but just the performance. |
| /// The consequences of using this method to make runtime and compile-time code behave |
| /// differently have not been explored. This method should not be used to introduce such |
| /// differences, and it should also not be stabilized before we have a better understanding |
| /// of this issue. |
| #[unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")] |
| #[inline] |
| pub const fn guaranteed_ne(self, other: *const T) -> Option<bool> |
| where |
| T: Sized, |
| { |
| match self.guaranteed_eq(other) { |
| None => None, |
| Some(eq) => Some(!eq), |
| } |
| } |
| |
| /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`). |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// If any of the following conditions are violated, the result is Undefined |
| /// Behavior: |
| /// |
| /// * If the computed offset is non-zero, then both the starting and resulting pointer must be |
| /// either in bounds or one byte past the end of the same [allocated object]. |
| /// (If it is zero, then the function is always well-defined.) |
| /// |
| /// * The computed offset, **in bytes**, cannot overflow an `isize`. |
| /// |
| /// * The offset being in bounds cannot rely on "wrapping around" the address |
| /// space. That is, the infinite-precision sum must fit in a `usize`. |
| /// |
| /// The compiler and standard library generally tries to ensure allocations |
| /// never reach a size where an offset is a concern. For instance, `Vec` |
| /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so |
| /// `vec.as_ptr().add(vec.len())` is always safe. |
| /// |
| /// Most platforms fundamentally can't even construct such an allocation. |
| /// For instance, no known 64-bit platform can ever serve a request |
| /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space. |
| /// However, some 32-bit and 16-bit platforms may successfully serve a request for |
| /// more than `isize::MAX` bytes with things like Physical Address |
| /// Extension. As such, memory acquired directly from allocators or memory |
| /// mapped files *may* be too large to handle with this function. |
| /// |
| /// Consider using [`wrapping_add`] instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// [`wrapping_add`]: #method.wrapping_add |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "123"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// |
| /// unsafe { |
| /// println!("{}", *ptr.add(1) as char); |
| /// println!("{}", *ptr.add(2) as char); |
| /// } |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn add(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| unsafe { intrinsics::offset(self, count) } |
| } |
| |
| /// Calculates the offset from a pointer in bytes (convenience for `.byte_offset(count as isize)`). |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [add][pointer::add] on it. See that method for documentation |
| /// and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn byte_add(self, count: usize) -> Self { |
| // SAFETY: the caller must uphold the safety contract for `add`. |
| unsafe { self.cast::<u8>().add(count).with_metadata_of(self) } |
| } |
| |
| /// Calculates the offset from a pointer (convenience for |
| /// `.offset((count as isize).wrapping_neg())`). |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// If any of the following conditions are violated, the result is Undefined |
| /// Behavior: |
| /// |
| /// * If the computed offset is non-zero, then both the starting and resulting pointer must be |
| /// either in bounds or one byte past the end of the same [allocated object]. |
| /// (If it is zero, then the function is always well-defined.) |
| /// |
| /// * The computed offset cannot exceed `isize::MAX` **bytes**. |
| /// |
| /// * The offset being in bounds cannot rely on "wrapping around" the address |
| /// space. That is, the infinite-precision sum must fit in a usize. |
| /// |
| /// The compiler and standard library generally tries to ensure allocations |
| /// never reach a size where an offset is a concern. For instance, `Vec` |
| /// and `Box` ensure they never allocate more than `isize::MAX` bytes, so |
| /// `vec.as_ptr().add(vec.len()).sub(vec.len())` is always safe. |
| /// |
| /// Most platforms fundamentally can't even construct such an allocation. |
| /// For instance, no known 64-bit platform can ever serve a request |
| /// for 2<sup>63</sup> bytes due to page-table limitations or splitting the address space. |
| /// However, some 32-bit and 16-bit platforms may successfully serve a request for |
| /// more than `isize::MAX` bytes with things like Physical Address |
| /// Extension. As such, memory acquired directly from allocators or memory |
| /// mapped files *may* be too large to handle with this function. |
| /// |
| /// Consider using [`wrapping_sub`] instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// [`wrapping_sub`]: #method.wrapping_sub |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let s: &str = "123"; |
| /// |
| /// unsafe { |
| /// let end: *const u8 = s.as_ptr().add(3); |
| /// println!("{}", *end.sub(1) as char); |
| /// println!("{}", *end.sub(2) as char); |
| /// } |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn sub(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| if T::IS_ZST { |
| // Pointer arithmetic does nothing when the pointee is a ZST. |
| self |
| } else { |
| // SAFETY: the caller must uphold the safety contract for `offset`. |
| // Because the pointee is *not* a ZST, that means that `count` is |
| // at most `isize::MAX`, and thus the negation cannot overflow. |
| unsafe { self.offset(intrinsics::unchecked_sub(0, count as isize)) } |
| } |
| } |
| |
| /// Calculates the offset from a pointer in bytes (convenience for |
| /// `.byte_offset((count as isize).wrapping_neg())`). |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [sub][pointer::sub] on it. See that method for documentation |
| /// and safety requirements. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn byte_sub(self, count: usize) -> Self { |
| // SAFETY: the caller must uphold the safety contract for `sub`. |
| unsafe { self.cast::<u8>().sub(count).with_metadata_of(self) } |
| } |
| |
| /// Calculates the offset from a pointer using wrapping arithmetic. |
| /// (convenience for `.wrapping_offset(count as isize)`) |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// This operation itself is always safe, but using the resulting pointer is not. |
| /// |
| /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not |
| /// be used to read or write other allocated objects. |
| /// |
| /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z` |
| /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still |
| /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless |
| /// `x` and `y` point into the same allocated object. |
| /// |
| /// Compared to [`add`], this method basically delays the requirement of staying within the |
| /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object |
| /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a |
| /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`] |
| /// can be optimized better and is thus preferable in performance-sensitive code. |
| /// |
| /// The delayed check only considers the value of the pointer that was dereferenced, not the |
| /// intermediate values used during the computation of the final result. For example, |
| /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the |
| /// allocated object and then re-entering it later is permitted. |
| /// |
| /// [`add`]: #method.add |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// // Iterate using a raw pointer in increments of two elements |
| /// let data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *const u8 = data.as_ptr(); |
| /// let step = 2; |
| /// let end_rounded_up = ptr.wrapping_add(6); |
| /// |
| /// // This loop prints "1, 3, 5, " |
| /// while ptr != end_rounded_up { |
| /// unsafe { |
| /// print!("{}, ", *ptr); |
| /// } |
| /// ptr = ptr.wrapping_add(step); |
| /// } |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| pub const fn wrapping_add(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| self.wrapping_offset(count as isize) |
| } |
| |
| /// Calculates the offset from a pointer in bytes using wrapping arithmetic. |
| /// (convenience for `.wrapping_byte_offset(count as isize)`) |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [wrapping_add][pointer::wrapping_add] on it. See that method for documentation. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| pub const fn wrapping_byte_add(self, count: usize) -> Self { |
| self.cast::<u8>().wrapping_add(count).with_metadata_of(self) |
| } |
| |
| /// Calculates the offset from a pointer using wrapping arithmetic. |
| /// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`) |
| /// |
| /// `count` is in units of T; e.g., a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// This operation itself is always safe, but using the resulting pointer is not. |
| /// |
| /// The resulting pointer "remembers" the [allocated object] that `self` points to; it must not |
| /// be used to read or write other allocated objects. |
| /// |
| /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z` |
| /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still |
| /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless |
| /// `x` and `y` point into the same allocated object. |
| /// |
| /// Compared to [`sub`], this method basically delays the requirement of staying within the |
| /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object |
| /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a |
| /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`] |
| /// can be optimized better and is thus preferable in performance-sensitive code. |
| /// |
| /// The delayed check only considers the value of the pointer that was dereferenced, not the |
| /// intermediate values used during the computation of the final result. For example, |
| /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the |
| /// allocated object and then re-entering it later is permitted. |
| /// |
| /// [`sub`]: #method.sub |
| /// [allocated object]: crate::ptr#allocated-object |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// // Iterate using a raw pointer in increments of two elements (backwards) |
| /// let data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *const u8 = data.as_ptr(); |
| /// let start_rounded_down = ptr.wrapping_sub(2); |
| /// ptr = ptr.wrapping_add(4); |
| /// let step = 2; |
| /// // This loop prints "5, 3, 1, " |
| /// while ptr != start_rounded_down { |
| /// unsafe { |
| /// print!("{}, ", *ptr); |
| /// } |
| /// ptr = ptr.wrapping_sub(step); |
| /// } |
| /// ``` |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[must_use = "returns a new pointer rather than modifying its argument"] |
| #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")] |
| #[inline(always)] |
| pub const fn wrapping_sub(self, count: usize) -> Self |
| where |
| T: Sized, |
| { |
| self.wrapping_offset((count as isize).wrapping_neg()) |
| } |
| |
| /// Calculates the offset from a pointer in bytes using wrapping arithmetic. |
| /// (convenience for `.wrapping_offset((count as isize).wrapping_neg())`) |
| /// |
| /// `count` is in units of bytes. |
| /// |
| /// This is purely a convenience for casting to a `u8` pointer and |
| /// using [wrapping_sub][pointer::wrapping_sub] on it. See that method for documentation. |
| /// |
| /// For non-`Sized` pointees this operation changes only the data pointer, |
| /// leaving the metadata untouched. |
| #[must_use] |
| #[inline(always)] |
| #[stable(feature = "pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_const_stable(feature = "const_pointer_byte_offsets", since = "1.75.0")] |
| #[rustc_allow_const_fn_unstable(set_ptr_value)] |
| pub const fn wrapping_byte_sub(self, count: usize) -> Self { |
| self.cast::<u8>().wrapping_sub(count).with_metadata_of(self) |
| } |
| |
| /// Reads the value from `self` without moving it. This leaves the |
| /// memory in `self` unchanged. |
| /// |
| /// See [`ptr::read`] for safety concerns and examples. |
| /// |
| /// [`ptr::read`]: crate::ptr::read() |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn read(self) -> T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `read`. |
| unsafe { read(self) } |
| } |
| |
| /// Performs a volatile read of the value from `self` without moving it. This |
| /// leaves the memory in `self` unchanged. |
| /// |
| /// Volatile operations are intended to act on I/O memory, and are guaranteed |
| /// to not be elided or reordered by the compiler across other volatile |
| /// operations. |
| /// |
| /// See [`ptr::read_volatile`] for safety concerns and examples. |
| /// |
| /// [`ptr::read_volatile`]: crate::ptr::read_volatile() |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub unsafe fn read_volatile(self) -> T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `read_volatile`. |
| unsafe { read_volatile(self) } |
| } |
| |
| /// Reads the value from `self` without moving it. This leaves the |
| /// memory in `self` unchanged. |
| /// |
| /// Unlike `read`, the pointer may be unaligned. |
| /// |
| /// See [`ptr::read_unaligned`] for safety concerns and examples. |
| /// |
| /// [`ptr::read_unaligned`]: crate::ptr::read_unaligned() |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn read_unaligned(self) -> T |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `read_unaligned`. |
| unsafe { read_unaligned(self) } |
| } |
| |
| /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source |
| /// and destination may overlap. |
| /// |
| /// NOTE: this has the *same* argument order as [`ptr::copy`]. |
| /// |
| /// See [`ptr::copy`] for safety concerns and examples. |
| /// |
| /// [`ptr::copy`]: crate::ptr::copy() |
| #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")] |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn copy_to(self, dest: *mut T, count: usize) |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `copy`. |
| unsafe { copy(self, dest, count) } |
| } |
| |
| /// Copies `count * size_of<T>` bytes from `self` to `dest`. The source |
| /// and destination may *not* overlap. |
| /// |
| /// NOTE: this has the *same* argument order as [`ptr::copy_nonoverlapping`]. |
| /// |
| /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples. |
| /// |
| /// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping() |
| #[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")] |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces |
| pub const unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize) |
| where |
| T: Sized, |
| { |
| // SAFETY: the caller must uphold the safety contract for `copy_nonoverlapping`. |
| unsafe { copy_nonoverlapping(self, dest, count) } |
| } |
| |
| /// Computes the offset that needs to be applied to the pointer in order to make it aligned to |
| /// `align`. |
| /// |
| /// If it is not possible to align the pointer, the implementation returns |
| /// `usize::MAX`. |
| /// |
| /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be |
| /// used with the `wrapping_add` method. |
| /// |
| /// There are no guarantees whatsoever that offsetting the pointer will not overflow or go |
| /// beyond the allocation that the pointer points into. It is up to the caller to ensure that |
| /// the returned offset is correct in all terms other than alignment. |
| /// |
| /// When this is called during compile-time evaluation (which is unstable), the implementation |
| /// may return `usize::MAX` in cases where that can never happen at runtime. This is because the |
| /// actual alignment of pointers is not known yet during compile-time, so an offset with |
| /// guaranteed alignment can sometimes not be computed. For example, a buffer declared as `[u8; |
| /// N]` might be allocated at an odd or an even address, but at compile-time this is not yet |
| /// known, so the execution has to be correct for either choice. It is therefore impossible to |
| /// find an offset that is guaranteed to be 2-aligned. (This behavior is subject to change, as usual |
| /// for unstable APIs.) |
| /// |
| /// # Panics |
| /// |
| /// The function panics if `align` is not a power-of-two. |
| /// |
| /// # Examples |
| /// |
| /// Accessing adjacent `u8` as `u16` |
| /// |
| /// ``` |
| /// use std::mem::align_of; |
| /// |
| /// # unsafe { |
| /// let x = [5_u8, 6, 7, 8, 9]; |
| /// let ptr = x.as_ptr(); |
| /// let offset = ptr.align_offset(align_of::<u16>()); |
| /// |
| /// if offset < x.len() - 1 { |
| /// let u16_ptr = ptr.add(offset).cast::<u16>(); |
| /// assert!(*u16_ptr == u16::from_ne_bytes([5, 6]) || *u16_ptr == u16::from_ne_bytes([6, 7])); |
| /// } else { |
| /// // while the pointer can be aligned via `offset`, it would point |
| /// // outside the allocation |
| /// } |
| /// # } |
| /// ``` |
| #[must_use] |
| #[inline] |
| #[stable(feature = "align_offset", since = "1.36.0")] |
| #[rustc_const_unstable(feature = "const_align_offset", issue = "90962")] |
| pub const fn align_offset(self, align: usize) -> usize |
| where |
| T: Sized, |
| { |
| if !align.is_power_of_two() { |
| panic!("align_offset: align is not a power-of-two"); |
| } |
| |
| // SAFETY: `align` has been checked to be a power of 2 above |
| let ret = unsafe { align_offset(self, align) }; |
| |
| // Inform Miri that we want to consider the resulting pointer to be suitably aligned. |
| #[cfg(miri)] |
| if ret != usize::MAX { |
| intrinsics::miri_promise_symbolic_alignment(self.wrapping_add(ret).cast(), align); |
| } |
| |
| ret |
| } |
| |
| /// Returns whether the pointer is properly aligned for `T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// // On some platforms, the alignment of i32 is less than 4. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// |
| /// let data = AlignedI32(42); |
| /// let ptr = &data as *const AlignedI32; |
| /// |
| /// assert!(ptr.is_aligned()); |
| /// assert!(!ptr.wrapping_byte_add(1).is_aligned()); |
| /// ``` |
| /// |
| /// # At compiletime |
| /// **Note: Alignment at compiletime is experimental and subject to change. See the |
| /// [tracking issue] for details.** |
| /// |
| /// At compiletime, the compiler may not know where a value will end up in memory. |
| /// Calling this function on a pointer created from a reference at compiletime will only |
| /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer |
| /// is never aligned if cast to a type with a stricter alignment than the reference's |
| /// underlying allocation. |
| /// |
| /// ``` |
| /// #![feature(const_pointer_is_aligned)] |
| /// |
| /// // On some platforms, the alignment of primitives is less than their size. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// #[repr(align(8))] |
| /// struct AlignedI64(i64); |
| /// |
| /// const _: () = { |
| /// let data = AlignedI32(42); |
| /// let ptr = &data as *const AlignedI32; |
| /// assert!(ptr.is_aligned()); |
| /// |
| /// // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned. |
| /// let ptr1 = ptr.cast::<AlignedI64>(); |
| /// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>(); |
| /// assert!(!ptr1.is_aligned()); |
| /// assert!(!ptr2.is_aligned()); |
| /// }; |
| /// ``` |
| /// |
| /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime |
| /// pointer is aligned, even if the compiletime pointer wasn't aligned. |
| /// |
| /// ``` |
| /// #![feature(const_pointer_is_aligned)] |
| /// |
| /// // On some platforms, the alignment of primitives is less than their size. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// #[repr(align(8))] |
| /// struct AlignedI64(i64); |
| /// |
| /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned. |
| /// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42); |
| /// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned()); |
| /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned()); |
| /// |
| /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned. |
| /// let runtime_ptr = COMPTIME_PTR; |
| /// assert_ne!( |
| /// runtime_ptr.cast::<AlignedI64>().is_aligned(), |
| /// runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(), |
| /// ); |
| /// ``` |
| /// |
| /// If a pointer is created from a fixed address, this function behaves the same during |
| /// runtime and compiletime. |
| /// |
| /// ``` |
| /// #![feature(const_pointer_is_aligned)] |
| /// |
| /// // On some platforms, the alignment of primitives is less than their size. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// #[repr(align(8))] |
| /// struct AlignedI64(i64); |
| /// |
| /// const _: () = { |
| /// let ptr = 40 as *const AlignedI32; |
| /// assert!(ptr.is_aligned()); |
| /// |
| /// // For pointers with a known address, runtime and compiletime behavior are identical. |
| /// let ptr1 = ptr.cast::<AlignedI64>(); |
| /// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>(); |
| /// assert!(ptr1.is_aligned()); |
| /// assert!(!ptr2.is_aligned()); |
| /// }; |
| /// ``` |
| /// |
| /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203 |
| #[must_use] |
| #[inline] |
| #[stable(feature = "pointer_is_aligned", since = "1.79.0")] |
| #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")] |
| pub const fn is_aligned(self) -> bool |
| where |
| T: Sized, |
| { |
| self.is_aligned_to(mem::align_of::<T>()) |
| } |
| |
| /// Returns whether the pointer is aligned to `align`. |
| /// |
| /// For non-`Sized` pointees this operation considers only the data pointer, |
| /// ignoring the metadata. |
| /// |
| /// # Panics |
| /// |
| /// The function panics if `align` is not a power-of-two (this includes 0). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(pointer_is_aligned_to)] |
| /// |
| /// // On some platforms, the alignment of i32 is less than 4. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// |
| /// let data = AlignedI32(42); |
| /// let ptr = &data as *const AlignedI32; |
| /// |
| /// assert!(ptr.is_aligned_to(1)); |
| /// assert!(ptr.is_aligned_to(2)); |
| /// assert!(ptr.is_aligned_to(4)); |
| /// |
| /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2)); |
| /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4)); |
| /// |
| /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8)); |
| /// ``` |
| /// |
| /// # At compiletime |
| /// **Note: Alignment at compiletime is experimental and subject to change. See the |
| /// [tracking issue] for details.** |
| /// |
| /// At compiletime, the compiler may not know where a value will end up in memory. |
| /// Calling this function on a pointer created from a reference at compiletime will only |
| /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer |
| /// cannot be stricter aligned than the reference's underlying allocation. |
| /// |
| /// ``` |
| /// #![feature(pointer_is_aligned_to)] |
| /// #![feature(const_pointer_is_aligned)] |
| /// |
| /// // On some platforms, the alignment of i32 is less than 4. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// |
| /// const _: () = { |
| /// let data = AlignedI32(42); |
| /// let ptr = &data as *const AlignedI32; |
| /// |
| /// assert!(ptr.is_aligned_to(1)); |
| /// assert!(ptr.is_aligned_to(2)); |
| /// assert!(ptr.is_aligned_to(4)); |
| /// |
| /// // At compiletime, we know for sure that the pointer isn't aligned to 8. |
| /// assert!(!ptr.is_aligned_to(8)); |
| /// assert!(!ptr.wrapping_add(1).is_aligned_to(8)); |
| /// }; |
| /// ``` |
| /// |
| /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime |
| /// pointer is aligned, even if the compiletime pointer wasn't aligned. |
| /// |
| /// ``` |
| /// #![feature(pointer_is_aligned_to)] |
| /// #![feature(const_pointer_is_aligned)] |
| /// |
| /// // On some platforms, the alignment of i32 is less than 4. |
| /// #[repr(align(4))] |
| /// struct AlignedI32(i32); |
| /// |
| /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned. |
| /// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42); |
| /// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8)); |
| /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8)); |
| /// |
| /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned. |
| /// let runtime_ptr = COMPTIME_PTR; |
| /// assert_ne!( |
| /// runtime_ptr.is_aligned_to(8), |
| /// runtime_ptr.wrapping_add(1).is_aligned_to(8), |
| /// ); |
| /// ``` |
| /// |
| /// If a pointer is created from a fixed address, this function behaves the same during |
| /// runtime and compiletime. |
| /// |
| /// ``` |
| /// #![feature(pointer_is_aligned_to)] |
| /// #![feature(const_pointer_is_aligned)] |
| /// |
| /// const _: () = { |
| /// let ptr = 40 as *const u8; |
| /// assert!(ptr.is_aligned_to(1)); |
| /// assert!(ptr.is_aligned_to(2)); |
| /// assert!(ptr.is_aligned_to(4)); |
| /// assert!(ptr.is_aligned_to(8)); |
| /// assert!(!ptr.is_aligned_to(16)); |
| /// }; |
| /// ``` |
| /// |
| /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203 |
| #[must_use] |
| #[inline] |
| #[unstable(feature = "pointer_is_aligned_to", issue = "96284")] |
| #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")] |
| pub const fn is_aligned_to(self, align: usize) -> bool { |
| if !align.is_power_of_two() { |
| panic!("is_aligned_to: align is not a power-of-two"); |
| } |
| |
| #[inline] |
| fn runtime_impl(ptr: *const (), align: usize) -> bool { |
| ptr.addr() & (align - 1) == 0 |
| } |
| |
| #[inline] |
| const fn const_impl(ptr: *const (), align: usize) -> bool { |
| // We can't use the address of `self` in a `const fn`, so we use `align_offset` instead. |
| ptr.align_offset(align) == 0 |
| } |
| |
| // The cast to `()` is used to |
| // 1. deal with fat pointers; and |
| // 2. ensure that `align_offset` (in `const_impl`) doesn't actually try to compute an offset. |
| const_eval_select((self.cast::<()>(), align), const_impl, runtime_impl) |
| } |
| } |
| |
| impl<T> *const [T] { |
| /// Returns the length of a raw slice. |
| /// |
| /// The returned value is the number of **elements**, not the number of bytes. |
| /// |
| /// This function is safe, even when the raw slice cannot be cast to a slice |
| /// reference because the pointer is null or unaligned. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// use std::ptr; |
| /// |
| /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); |
| /// assert_eq!(slice.len(), 3); |
| /// ``` |
| #[inline] |
| #[stable(feature = "slice_ptr_len", since = "1.79.0")] |
| #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")] |
| #[rustc_allow_const_fn_unstable(ptr_metadata)] |
| pub const fn len(self) -> usize { |
| metadata(self) |
| } |
| |
| /// Returns `true` if the raw slice has a length of 0. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); |
| /// assert!(!slice.is_empty()); |
| /// ``` |
| #[inline(always)] |
| #[stable(feature = "slice_ptr_len", since = "1.79.0")] |
| #[rustc_const_stable(feature = "const_slice_ptr_len", since = "1.79.0")] |
| pub const fn is_empty(self) -> bool { |
| self.len() == 0 |
| } |
| |
| /// Returns a raw pointer to the slice's buffer. |
| /// |
| /// This is equivalent to casting `self` to `*const T`, but more type-safe. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// #![feature(slice_ptr_get)] |
| /// use std::ptr; |
| /// |
| /// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3); |
| /// assert_eq!(slice.as_ptr(), ptr::null()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "slice_ptr_get", issue = "74265")] |
| #[rustc_const_unstable(feature = "slice_ptr_get", issue = "74265")] |
| pub const fn as_ptr(self) -> *const T { |
| self as *const T |
| } |
| |
| /// Returns a raw pointer to an element or subslice, without doing bounds |
| /// checking. |
| /// |
| /// Calling this method with an out-of-bounds index or when `self` is not dereferenceable |
| /// is *[undefined behavior]* even if the resulting pointer is not used. |
| /// |
| /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(slice_ptr_get)] |
| /// |
| /// let x = &[1, 2, 4] as *const [i32]; |
| /// |
| /// unsafe { |
| /// assert_eq!(x.get_unchecked(1), x.as_ptr().add(1)); |
| /// } |
| /// ``` |
| #[unstable(feature = "slice_ptr_get", issue = "74265")] |
| #[inline] |
| pub unsafe fn get_unchecked<I>(self, index: I) -> *const I::Output |
| where |
| I: SliceIndex<[T]>, |
| { |
| // SAFETY: the caller ensures that `self` is dereferenceable and `index` in-bounds. |
| unsafe { index.get_unchecked(self) } |
| } |
| |
| /// Returns `None` if the pointer is null, or else returns a shared slice to |
| /// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require |
| /// that the value has to be initialized. |
| /// |
| /// [`as_ref`]: #method.as_ref |
| /// |
| /// # Safety |
| /// |
| /// When calling this method, you have to ensure that *either* the pointer is null *or* |
| /// all of the following is true: |
| /// |
| /// * The pointer must be [valid] for reads for `ptr.len() * mem::size_of::<T>()` many bytes, |
| /// and it must be properly aligned. This means in particular: |
| /// |
| /// * The entire memory range of this slice must be contained within a single [allocated object]! |
| /// Slices can never span across multiple allocated objects. |
| /// |
| /// * The pointer must be aligned even for zero-length slices. One |
| /// reason for this is that enum layout optimizations may rely on references |
| /// (including slices of any length) being aligned and non-null to distinguish |
| /// them from other data. You can obtain a pointer that is usable as `data` |
| /// for zero-length slices using [`NonNull::dangling()`]. |
| /// |
| /// * The total size `ptr.len() * mem::size_of::<T>()` of the slice must be no larger than `isize::MAX`. |
| /// See the safety documentation of [`pointer::offset`]. |
| /// |
| /// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is |
| /// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data. |
| /// In particular, while this reference exists, the memory the pointer points to must |
| /// not get mutated (except inside `UnsafeCell`). |
| /// |
| /// This applies even if the result of this method is unused! |
| /// |
| /// See also [`slice::from_raw_parts`][]. |
| /// |
| /// [valid]: crate::ptr#safety |
| /// [allocated object]: crate::ptr#allocated-object |
| #[inline] |
| #[unstable(feature = "ptr_as_uninit", issue = "75402")] |
| #[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")] |
| pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]> { |
| if self.is_null() { |
| None |
| } else { |
| // SAFETY: the caller must uphold the safety contract for `as_uninit_slice`. |
| Some(unsafe { slice::from_raw_parts(self as *const MaybeUninit<T>, self.len()) }) |
| } |
| } |
| } |
| |
| impl<T, const N: usize> *const [T; N] { |
| /// Returns a raw pointer to the array's buffer. |
| /// |
| /// This is equivalent to casting `self` to `*const T`, but more type-safe. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// #![feature(array_ptr_get)] |
| /// use std::ptr; |
| /// |
| /// let arr: *const [i8; 3] = ptr::null(); |
| /// assert_eq!(arr.as_ptr(), ptr::null()); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "array_ptr_get", issue = "119834")] |
| #[rustc_const_unstable(feature = "array_ptr_get", issue = "119834")] |
| pub const fn as_ptr(self) -> *const T { |
| self as *const T |
| } |
| |
| /// Returns a raw pointer to a slice containing the entire array. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(array_ptr_get)] |
| /// |
| /// let arr: *const [i32; 3] = &[1, 2, 4] as *const [i32; 3]; |
| /// let slice: *const [i32] = arr.as_slice(); |
| /// assert_eq!(slice.len(), 3); |
| /// ``` |
| #[inline] |
| #[unstable(feature = "array_ptr_get", issue = "119834")] |
| #[rustc_const_unstable(feature = "array_ptr_get", issue = "119834")] |
| pub const fn as_slice(self) -> *const [T] { |
| self |
| } |
| } |
| |
| // Equality for pointers |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> PartialEq for *const T { |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn eq(&self, other: &*const T) -> bool { |
| *self == *other |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> Eq for *const T {} |
| |
| // Comparison for pointers |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> Ord for *const T { |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn cmp(&self, other: &*const T) -> Ordering { |
| if self < other { |
| Less |
| } else if self == other { |
| Equal |
| } else { |
| Greater |
| } |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> PartialOrd for *const T { |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn partial_cmp(&self, other: &*const T) -> Option<Ordering> { |
| Some(self.cmp(other)) |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn lt(&self, other: &*const T) -> bool { |
| *self < *other |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn le(&self, other: &*const T) -> bool { |
| *self <= *other |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn gt(&self, other: &*const T) -> bool { |
| *self > *other |
| } |
| |
| #[inline] |
| #[allow(ambiguous_wide_pointer_comparisons)] |
| fn ge(&self, other: &*const T) -> bool { |
| *self >= *other |
| } |
| } |