1541 lines
63 KiB
Rust
1541 lines
63 KiB
Rust
use super::*;
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use crate::cmp::Ordering::{self, Equal, Greater, Less};
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use crate::intrinsics;
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use crate::mem;
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use crate::slice::{self, SliceIndex};
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impl<T: ?Sized> *const T {
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/// Returns `true` if the pointer is null.
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///
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/// Note that unsized types have many possible null pointers, as only the
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/// raw data pointer is considered, not their length, vtable, etc.
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/// Therefore, two pointers that are null may still not compare equal to
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/// each other.
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///
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/// ## Behavior during const evaluation
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///
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/// When this function is used during const evaluation, it may return `false` for pointers
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/// that turn out to be null at runtime. Specifically, when a pointer to some memory
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/// is offset beyond its bounds in such a way that the resulting pointer is null,
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/// the function will still return `false`. There is no way for CTFE to know
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/// the absolute position of that memory, so we cannot tell if the pointer is
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/// null or not.
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let s: &str = "Follow the rabbit";
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/// let ptr: *const u8 = s.as_ptr();
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/// assert!(!ptr.is_null());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
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#[inline]
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pub const fn is_null(self) -> bool {
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// Compare via a cast to a thin pointer, so fat pointers are only
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// considering their "data" part for null-ness.
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(self as *const u8).guaranteed_eq(null())
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}
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/// Casts to a pointer of another type.
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#[stable(feature = "ptr_cast", since = "1.38.0")]
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#[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
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#[inline]
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pub const fn cast<U>(self) -> *const U {
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self as _
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}
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/// Use the pointer value in a new pointer of another type.
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///
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/// In case `val` is a (fat) pointer to an unsized type, this operation
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/// will ignore the pointer part, whereas for (thin) pointers to sized
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/// types, this has the same effect as a simple cast.
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///
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/// The resulting pointer will have provenance of `self`, i.e., for a fat
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/// pointer, this operation is semantically the same as creating a new
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/// fat pointer with the data pointer value of `self` but the metadata of
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/// `val`.
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///
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/// # Examples
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///
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/// This function is primarily useful for allowing byte-wise pointer
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/// arithmetic on potentially fat pointers:
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///
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/// ```
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/// #![feature(set_ptr_value)]
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/// # use core::fmt::Debug;
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/// let arr: [i32; 3] = [1, 2, 3];
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/// let mut ptr = arr.as_ptr() as *const dyn Debug;
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/// let thin = ptr as *const u8;
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/// unsafe {
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/// ptr = thin.add(8).with_metadata_of(ptr);
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/// # assert_eq!(*(ptr as *const i32), 3);
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/// println!("{:?}", &*ptr); // will print "3"
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/// }
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/// ```
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#[unstable(feature = "set_ptr_value", issue = "75091")]
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#[must_use = "returns a new pointer rather than modifying its argument"]
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#[inline]
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pub fn with_metadata_of<U>(self, mut val: *const U) -> *const U
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where
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U: ?Sized,
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{
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let target = &mut val as *mut *const U as *mut *const u8;
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// SAFETY: In case of a thin pointer, this operations is identical
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// to a simple assignment. In case of a fat pointer, with the current
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// fat pointer layout implementation, the first field of such a
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// pointer is always the data pointer, which is likewise assigned.
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unsafe { *target = self as *const u8 };
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val
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}
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/// Changes constness without changing the type.
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///
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/// This is a bit safer than `as` because it wouldn't silently change the type if the code is
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/// refactored.
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#[stable(feature = "ptr_const_cast", since = "CURRENT_RUSTC_VERSION")]
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#[rustc_const_stable(feature = "ptr_const_cast", since = "CURRENT_RUSTC_VERSION")]
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pub const fn cast_mut(self) -> *mut T {
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self as _
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}
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/// Casts a pointer to its raw bits.
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///
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/// This is equivalent to `as usize`, but is more specific to enhance readability.
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/// The inverse method is [`from_bits`](#method.from_bits).
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///
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/// In particular, `*p as usize` and `p as usize` will both compile for
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/// pointers to numeric types but do very different things, so using this
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/// helps emphasize that reading the bits was intentional.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(ptr_to_from_bits)]
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/// let array = [13, 42];
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/// let p0: *const i32 = &array[0];
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/// assert_eq!(<*const _>::from_bits(p0.to_bits()), p0);
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/// let p1: *const i32 = &array[1];
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/// assert_eq!(p1.to_bits() - p0.to_bits(), 4);
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/// ```
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#[unstable(feature = "ptr_to_from_bits", issue = "91126")]
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pub fn to_bits(self) -> usize
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where
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T: Sized,
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{
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self as usize
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}
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/// Creates a pointer from its raw bits.
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///
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/// This is equivalent to `as *const T`, but is more specific to enhance readability.
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/// The inverse method is [`to_bits`](#method.to_bits).
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///
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/// # Examples
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///
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/// ```
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/// #![feature(ptr_to_from_bits)]
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/// use std::ptr::NonNull;
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/// let dangling: *const u8 = NonNull::dangling().as_ptr();
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/// assert_eq!(<*const u8>::from_bits(1), dangling);
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/// ```
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#[unstable(feature = "ptr_to_from_bits", issue = "91126")]
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pub fn from_bits(bits: usize) -> Self
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where
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T: Sized,
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{
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bits as Self
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}
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/// Gets the "address" portion of the pointer.
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///
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/// This is similar to `self as usize`, which semantically discards *provenance* and
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/// *address-space* information. However, unlike `self as usize`, casting the returned address
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/// back to a pointer yields [`invalid`][], which is undefined behavior to dereference. To
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/// properly restore the lost information and obtain a dereferenceable pointer, use
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/// [`with_addr`][pointer::with_addr] or [`map_addr`][pointer::map_addr].
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///
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/// If using those APIs is not possible because there is no way to preserve a pointer with the
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/// required provenance, use [`expose_addr`][pointer::expose_addr] and
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/// [`from_exposed_addr`][from_exposed_addr] instead. However, note that this makes
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/// your code less portable and less amenable to tools that check for compliance with the Rust
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/// memory model.
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///
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/// On most platforms this will produce a value with the same bytes as the original
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/// pointer, because all the bytes are dedicated to describing the address.
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/// Platforms which need to store additional information in the pointer may
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/// perform a change of representation to produce a value containing only the address
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/// portion of the pointer. What that means is up to the platform to define.
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///
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/// This API and its claimed semantics are part of the Strict Provenance experiment, and as such
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/// might change in the future (including possibly weakening this so it becomes wholly
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/// equivalent to `self as usize`). See the [module documentation][crate::ptr] for details.
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#[must_use]
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#[inline]
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#[unstable(feature = "strict_provenance", issue = "95228")]
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pub fn addr(self) -> usize
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where
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T: Sized,
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{
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// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
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// SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the
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// provenance).
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unsafe { mem::transmute(self) }
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}
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/// Gets the "address" portion of the pointer, and 'exposes' the "provenance" part for future
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/// use in [`from_exposed_addr`][].
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///
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/// This is equivalent to `self as usize`, which semantically discards *provenance* and
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/// *address-space* information. Furthermore, this (like the `as` cast) has the implicit
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/// side-effect of marking the provenance as 'exposed', so on platforms that support it you can
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/// later call [`from_exposed_addr`][] to reconstitute the original pointer including its
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/// provenance. (Reconstructing address space information, if required, is your responsibility.)
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///
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/// Using this method means that code is *not* following Strict Provenance rules. Supporting
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/// [`from_exposed_addr`][] complicates specification and reasoning and may not be supported by
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/// tools that help you to stay conformant with the Rust memory model, so it is recommended to
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/// use [`addr`][pointer::addr] wherever possible.
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///
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/// On most platforms this will produce a value with the same bytes as the original pointer,
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/// because all the bytes are dedicated to describing the address. Platforms which need to store
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/// additional information in the pointer may not support this operation, since the 'expose'
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/// side-effect which is required for [`from_exposed_addr`][] to work is typically not
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/// available.
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///
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/// This API and its claimed semantics are part of the Strict Provenance experiment, see the
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/// [module documentation][crate::ptr] for details.
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///
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/// [`from_exposed_addr`]: from_exposed_addr
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#[must_use]
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#[inline]
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#[unstable(feature = "strict_provenance", issue = "95228")]
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pub fn expose_addr(self) -> usize
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where
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T: Sized,
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{
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// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
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self as usize
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}
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/// Creates a new pointer with the given address.
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///
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/// This performs the same operation as an `addr as ptr` cast, but copies
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/// the *address-space* and *provenance* of `self` to the new pointer.
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/// This allows us to dynamically preserve and propagate this important
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/// information in a way that is otherwise impossible with a unary cast.
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///
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/// This is equivalent to using [`wrapping_offset`][pointer::wrapping_offset] to offset
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/// `self` to the given address, and therefore has all the same capabilities and restrictions.
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///
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/// This API and its claimed semantics are part of the Strict Provenance experiment,
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/// see the [module documentation][crate::ptr] for details.
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#[must_use]
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#[inline]
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#[unstable(feature = "strict_provenance", issue = "95228")]
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pub fn with_addr(self, addr: usize) -> Self
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where
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T: Sized,
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{
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// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
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//
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// In the mean-time, this operation is defined to be "as if" it was
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// a wrapping_offset, so we can emulate it as such. This should properly
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// restore pointer provenance even under today's compiler.
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let self_addr = self.addr() as isize;
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let dest_addr = addr as isize;
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let offset = dest_addr.wrapping_sub(self_addr);
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// This is the canonical desugarring of this operation
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self.wrapping_byte_offset(offset)
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}
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/// Creates a new pointer by mapping `self`'s address to a new one.
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///
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/// This is a convenience for [`with_addr`][pointer::with_addr], see that method for details.
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///
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/// This API and its claimed semantics are part of the Strict Provenance experiment,
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/// see the [module documentation][crate::ptr] for details.
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#[must_use]
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#[inline]
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#[unstable(feature = "strict_provenance", issue = "95228")]
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pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self
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where
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T: Sized,
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{
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self.with_addr(f(self.addr()))
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}
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/// Decompose a (possibly wide) pointer into its address and metadata components.
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///
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/// The pointer can be later reconstructed with [`from_raw_parts`].
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#[unstable(feature = "ptr_metadata", issue = "81513")]
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#[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
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#[inline]
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pub const fn to_raw_parts(self) -> (*const (), <T as super::Pointee>::Metadata) {
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(self.cast(), metadata(self))
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}
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/// Returns `None` if the pointer is null, or else returns a shared reference to
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/// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`]
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/// must be used instead.
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///
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/// [`as_uninit_ref`]: #method.as_uninit_ref
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///
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/// # Safety
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///
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/// When calling this method, you have to ensure that *either* the pointer is null *or*
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/// all of the following is true:
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///
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/// * The pointer must be properly aligned.
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///
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/// * It must be "dereferenceable" in the sense defined in [the module documentation].
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///
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/// * The pointer must point to an initialized instance of `T`.
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///
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/// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
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/// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
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/// In particular, while this reference exists, the memory the pointer points to must
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/// not get mutated (except inside `UnsafeCell`).
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///
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/// This applies even if the result of this method is unused!
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/// (The part about being initialized is not yet fully decided, but until
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/// it is, the only safe approach is to ensure that they are indeed initialized.)
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///
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/// [the module documentation]: crate::ptr#safety
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let ptr: *const u8 = &10u8 as *const u8;
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///
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/// unsafe {
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/// if let Some(val_back) = ptr.as_ref() {
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/// println!("We got back the value: {val_back}!");
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/// }
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/// }
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/// ```
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///
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/// # Null-unchecked version
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///
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/// If you are sure the pointer can never be null and are looking for some kind of
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/// `as_ref_unchecked` that returns the `&T` instead of `Option<&T>`, know that you can
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/// dereference the pointer directly.
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///
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/// ```
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/// let ptr: *const u8 = &10u8 as *const u8;
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///
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/// unsafe {
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/// let val_back = &*ptr;
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/// println!("We got back the value: {val_back}!");
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/// }
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/// ```
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#[stable(feature = "ptr_as_ref", since = "1.9.0")]
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#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
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#[inline]
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pub const unsafe fn as_ref<'a>(self) -> Option<&'a T> {
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// SAFETY: the caller must guarantee that `self` is valid
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// for a reference if it isn't null.
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if self.is_null() { None } else { unsafe { Some(&*self) } }
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}
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/// Returns `None` if the pointer is null, or else returns a shared reference to
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/// the value wrapped in `Some`. In contrast to [`as_ref`], this does not require
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/// that the value has to be initialized.
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///
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/// [`as_ref`]: #method.as_ref
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///
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/// # Safety
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///
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/// When calling this method, you have to ensure that *either* the pointer is null *or*
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/// all of the following is true:
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///
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/// * The pointer must be properly aligned.
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///
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/// * It must be "dereferenceable" in the sense defined in [the module documentation].
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///
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/// * You must enforce Rust's aliasing rules, since the returned lifetime `'a` is
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/// arbitrarily chosen and does not necessarily reflect the actual lifetime of the data.
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/// In particular, while this reference exists, the memory the pointer points to must
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/// not get mutated (except inside `UnsafeCell`).
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///
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/// This applies even if the result of this method is unused!
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///
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/// [the module documentation]: crate::ptr#safety
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///
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/// # Examples
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///
|
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/// Basic usage:
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///
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/// ```
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/// #![feature(ptr_as_uninit)]
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///
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/// let ptr: *const u8 = &10u8 as *const u8;
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///
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/// unsafe {
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/// if let Some(val_back) = ptr.as_uninit_ref() {
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/// println!("We got back the value: {}!", val_back.assume_init());
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/// }
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/// }
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/// ```
|
|
#[inline]
|
|
#[unstable(feature = "ptr_as_uninit", issue = "75402")]
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#[rustc_const_unstable(feature = "const_ptr_as_ref", issue = "91822")]
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pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
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where
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T: Sized,
|
|
{
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// SAFETY: the caller must guarantee that `self` meets all the
|
|
// requirements for a reference.
|
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if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
|
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}
|
|
|
|
/// 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:
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|
///
|
|
/// * Both the starting and resulting pointer must be either in bounds or one
|
|
/// byte past the end of the same [allocated object].
|
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///
|
|
/// * 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
|
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/// 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
|
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/// enables more aggressive compiler optimizations.
|
|
///
|
|
/// [`wrapping_offset`]: #method.wrapping_offset
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|
/// [allocated object]: crate::ptr#allocated-object
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|
///
|
|
/// # Examples
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// 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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
#[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`.
|
|
let this = unsafe { self.cast::<u8>().offset(count).cast::<()>() };
|
|
from_raw_parts::<T>(this, metadata(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
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// // 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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
pub const fn wrapping_byte_offset(self, count: isize) -> Self {
|
|
from_raw_parts::<T>(self.cast::<u8>().wrapping_offset(count).cast::<()>(), metadata(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.
|
|
#[cfg(not(bootstrap))]
|
|
#[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 {
|
|
let this = intrinsics::ptr_mask(self.cast::<()>(), mask);
|
|
from_raw_parts::<T>(this, metadata(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 function is the inverse of [`offset`].
|
|
///
|
|
/// [`offset`]: #method.offset
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// If any of the following conditions are violated, the result is Undefined
|
|
/// Behavior:
|
|
///
|
|
/// * Both the starting and other pointer must be either in bounds or one
|
|
/// byte past the end of the same [allocated object].
|
|
///
|
|
/// * Both pointers must be *derived from* a pointer to the same object.
|
|
/// (See below for an example.)
|
|
///
|
|
/// * 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.)
|
|
///
|
|
/// [`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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
|
|
pub const unsafe fn byte_offset_from(self, origin: *const T) -> 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 that the offset is
|
|
/// guaranteed to be non-negative. This method is equivalent to
|
|
/// `usize::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,
|
|
{
|
|
let this = self;
|
|
// SAFETY: The comparison has no side-effects, and the intrinsic
|
|
// does this check internally in the CTFE implementation.
|
|
unsafe {
|
|
assert_unsafe_precondition!([T](this: *const T, origin: *const T) => 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 `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 `false` for pointers that later actually turn out to be equal.
|
|
/// But when it returns `true`, the pointers are guaranteed to be equal.
|
|
///
|
|
/// This function is the mirror of [`guaranteed_ne`], but not its inverse. There are pointer
|
|
/// comparisons for which both functions return `false`.
|
|
///
|
|
/// [`guaranteed_ne`]: #method.guaranteed_ne
|
|
///
|
|
/// The return value may change 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 `false` 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) -> bool
|
|
where
|
|
T: Sized,
|
|
{
|
|
intrinsics::ptr_guaranteed_eq(self, other)
|
|
}
|
|
|
|
/// Returns whether two pointers are guaranteed to be unequal.
|
|
///
|
|
/// At runtime this function behaves like `self != other`.
|
|
/// However, in some contexts (e.g., compile-time evaluation),
|
|
/// it is not always possible to determine the inequality of two pointers, so this function may
|
|
/// spuriously return `false` for pointers that later actually turn out to be unequal.
|
|
/// But when it returns `true`, the pointers are guaranteed to be unequal.
|
|
///
|
|
/// This function is the mirror of [`guaranteed_eq`], but not its inverse. There are pointer
|
|
/// comparisons for which both functions return `false`.
|
|
///
|
|
/// [`guaranteed_eq`]: #method.guaranteed_eq
|
|
///
|
|
/// The return value may change 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 `false` 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) -> bool
|
|
where
|
|
T: Sized,
|
|
{
|
|
intrinsics::ptr_guaranteed_ne(self, other)
|
|
}
|
|
|
|
/// 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:
|
|
///
|
|
/// * Both the starting and resulting pointer must be either in bounds or one
|
|
/// byte past the end of the same [allocated object].
|
|
///
|
|
/// * 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
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// 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 { self.offset(count as isize) }
|
|
}
|
|
|
|
/// 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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
#[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`.
|
|
let this = unsafe { self.cast::<u8>().add(count).cast::<()>() };
|
|
from_raw_parts::<T>(this, metadata(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:
|
|
///
|
|
/// * Both the starting and resulting pointer must be either in bounds or one
|
|
/// byte past the end of the same [allocated object].
|
|
///
|
|
/// * 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
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// 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]
|
|
#[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,
|
|
{
|
|
// SAFETY: the caller must uphold the safety contract for `offset`.
|
|
unsafe { self.offset((count as isize).wrapping_neg()) }
|
|
}
|
|
|
|
/// 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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
#[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`.
|
|
let this = unsafe { self.cast::<u8>().sub(count).cast::<()>() };
|
|
from_raw_parts::<T>(this, metadata(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
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// // 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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
pub const fn wrapping_byte_add(self, count: usize) -> Self {
|
|
from_raw_parts::<T>(self.cast::<u8>().wrapping_add(count).cast::<()>(), metadata(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
|
|
///
|
|
/// Basic usage:
|
|
///
|
|
/// ```
|
|
/// // 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]
|
|
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)]
|
|
#[unstable(feature = "pointer_byte_offsets", issue = "96283")]
|
|
#[rustc_const_unstable(feature = "const_pointer_byte_offsets", issue = "96283")]
|
|
pub const fn wrapping_byte_sub(self, count: usize) -> Self {
|
|
from_raw_parts::<T>(self.cast::<u8>().wrapping_sub(count).cast::<()>(), metadata(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_unstable(feature = "const_ptr_read", issue = "80377")]
|
|
#[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_unstable(feature = "const_ptr_read", issue = "80377")]
|
|
#[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_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
|
|
#[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_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
|
|
#[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`. It is permissible for the implementation to *always*
|
|
/// return `usize::MAX`. Only your algorithm's performance can depend
|
|
/// on getting a usable offset here, not its correctness.
|
|
///
|
|
/// 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.
|
|
///
|
|
/// # 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
|
|
/// }
|
|
/// # }
|
|
/// ```
|
|
#[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");
|
|
}
|
|
|
|
fn rt_impl<T>(p: *const T, align: usize) -> usize {
|
|
// SAFETY: `align` has been checked to be a power of 2 above
|
|
unsafe { align_offset(p, align) }
|
|
}
|
|
|
|
const fn ctfe_impl<T>(_: *const T, _: usize) -> usize {
|
|
usize::MAX
|
|
}
|
|
|
|
// SAFETY:
|
|
// It is permissible for `align_offset` to always return `usize::MAX`,
|
|
// algorithm correctness can not depend on `align_offset` returning non-max values.
|
|
//
|
|
// As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
|
|
unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
|
|
}
|
|
|
|
/// Returns whether the pointer is properly aligned for `T`.
|
|
#[must_use]
|
|
#[inline]
|
|
#[unstable(feature = "pointer_is_aligned", issue = "96284")]
|
|
pub fn is_aligned(self) -> bool
|
|
where
|
|
T: Sized,
|
|
{
|
|
self.is_aligned_to(core::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).
|
|
#[must_use]
|
|
#[inline]
|
|
#[unstable(feature = "pointer_is_aligned", issue = "96284")]
|
|
pub 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");
|
|
}
|
|
|
|
// Cast is needed for `T: !Sized`
|
|
self.cast::<u8>().addr() & align - 1 == 0
|
|
}
|
|
}
|
|
|
|
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
|
|
/// #![feature(slice_ptr_len)]
|
|
///
|
|
/// use std::ptr;
|
|
///
|
|
/// let slice: *const [i8] = ptr::slice_from_raw_parts(ptr::null(), 3);
|
|
/// assert_eq!(slice.len(), 3);
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "slice_ptr_len", issue = "71146")]
|
|
#[rustc_const_unstable(feature = "const_slice_ptr_len", issue = "71146")]
|
|
pub const fn len(self) -> usize {
|
|
metadata(self)
|
|
}
|
|
|
|
/// 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")]
|
|
#[rustc_const_unstable(feature = "const_slice_index", issue = "none")]
|
|
#[inline]
|
|
pub const unsafe fn get_unchecked<I>(self, index: I) -> *const I::Output
|
|
where
|
|
I: ~const 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()) })
|
|
}
|
|
}
|
|
}
|
|
|
|
// Equality for pointers
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized> PartialEq for *const T {
|
|
#[inline]
|
|
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]
|
|
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]
|
|
fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
|
|
Some(self.cmp(other))
|
|
}
|
|
|
|
#[inline]
|
|
fn lt(&self, other: &*const T) -> bool {
|
|
*self < *other
|
|
}
|
|
|
|
#[inline]
|
|
fn le(&self, other: &*const T) -> bool {
|
|
*self <= *other
|
|
}
|
|
|
|
#[inline]
|
|
fn gt(&self, other: &*const T) -> bool {
|
|
*self > *other
|
|
}
|
|
|
|
#[inline]
|
|
fn ge(&self, other: &*const T) -> bool {
|
|
*self >= *other
|
|
}
|
|
}
|