| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! Manually manage memory through raw pointers. |
| //! |
| //! *[See also the pointer primitive types](../../std/primitive.pointer.html).* |
| //! |
| //! # Safety |
| //! |
| //! Many functions in this module take raw pointers as arguments and read from |
| //! or write to them. For this to be safe, these pointers must be *valid*. |
| //! Whether a pointer is valid depends on the operation it is used for |
| //! (read or write), and the extent of the memory that is accessed (i.e., |
| //! how many bytes are read/written). Most functions use `*mut T` and `*const T` |
| //! to access only a single value, in which case the documentation omits the size |
| //! and implicitly assumes it to be `size_of::<T>()` bytes. |
| //! |
| //! The precise rules for validity are not determined yet. The guarantees that are |
| //! provided at this point are very minimal: |
| //! |
| //! * A [null] pointer is *never* valid, not even for accesses of [size zero][zst]. |
| //! * All pointers (except for the null pointer) are valid for all operations of |
| //! [size zero][zst]. |
| //! * All accesses performed by functions in this module are *non-atomic* in the sense |
| //! of [atomic operations] used to synchronize between threads. This means it is |
| //! undefined behavior to perform two concurrent accesses to the same location from different |
| //! threads unless both accesses only read from memory. Notice that this explicitly |
| //! includes [`read_volatile`] and [`write_volatile`]: Volatile accesses cannot |
| //! be used for inter-thread synchronization. |
| //! * The result of casting a reference to a pointer is valid for as long as the |
| //! underlying object is live and no reference (just raw pointers) is used to |
| //! access the same memory. |
| //! |
| //! These axioms, along with careful use of [`offset`] for pointer arithmetic, |
| //! are enough to correctly implement many useful things in unsafe code. Stronger guarantees |
| //! will be provided eventually, as the [aliasing] rules are being determined. For more |
| //! information, see the [book] as well as the section in the reference devoted |
| //! to [undefined behavior][ub]. |
| //! |
| //! ## Alignment |
| //! |
| //! Valid raw pointers as defined above are not necessarily properly aligned (where |
| //! "proper" alignment is defined by the pointee type, i.e., `*const T` must be |
| //! aligned to `mem::align_of::<T>()`). However, most functions require their |
| //! arguments to be properly aligned, and will explicitly state |
| //! this requirement in their documentation. Notable exceptions to this are |
| //! [`read_unaligned`] and [`write_unaligned`]. |
| //! |
| //! When a function requires proper alignment, it does so even if the access |
| //! has size 0, i.e., even if memory is not actually touched. Consider using |
| //! [`NonNull::dangling`] in such cases. |
| //! |
| //! [aliasing]: ../../nomicon/aliasing.html |
| //! [book]: ../../book/ch19-01-unsafe-rust.html#dereferencing-a-raw-pointer |
| //! [ub]: ../../reference/behavior-considered-undefined.html |
| //! [null]: ./fn.null.html |
| //! [zst]: ../../nomicon/exotic-sizes.html#zero-sized-types-zsts |
| //! [atomic operations]: ../../std/sync/atomic/index.html |
| //! [`copy`]: ../../std/ptr/fn.copy.html |
| //! [`offset`]: ../../std/primitive.pointer.html#method.offset |
| //! [`read_unaligned`]: ./fn.read_unaligned.html |
| //! [`write_unaligned`]: ./fn.write_unaligned.html |
| //! [`read_volatile`]: ./fn.read_volatile.html |
| //! [`write_volatile`]: ./fn.write_volatile.html |
| //! [`NonNull::dangling`]: ./struct.NonNull.html#method.dangling |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| use convert::From; |
| use intrinsics; |
| use ops::{CoerceUnsized, DispatchFromDyn}; |
| use fmt; |
| use hash; |
| use marker::{PhantomData, Unsize}; |
| use mem::{self, MaybeUninit}; |
| use nonzero::NonZero; |
| |
| use cmp::Ordering::{self, Less, Equal, Greater}; |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub use intrinsics::copy_nonoverlapping; |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub use intrinsics::copy; |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub use intrinsics::write_bytes; |
| |
| /// Executes the destructor (if any) of the pointed-to value. |
| /// |
| /// This is semantically equivalent to calling [`ptr::read`] and discarding |
| /// the result, but has the following advantages: |
| /// |
| /// * It is *required* to use `drop_in_place` to drop unsized types like |
| /// trait objects, because they can't be read out onto the stack and |
| /// dropped normally. |
| /// |
| /// * It is friendlier to the optimizer to do this over [`ptr::read`] when |
| /// dropping manually allocated memory (e.g. when writing Box/Rc/Vec), |
| /// as the compiler doesn't need to prove that it's sound to elide the |
| /// copy. |
| /// |
| /// [`ptr::read`]: ../ptr/fn.read.html |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `to_drop` must be [valid] for reads. |
| /// |
| /// * `to_drop` must be properly aligned. See the example below for how to drop |
| /// an unaligned pointer. |
| /// |
| /// Additionally, if `T` is not [`Copy`], using the pointed-to value after |
| /// calling `drop_in_place` can cause undefined behavior. Note that `*to_drop = |
| /// foo` counts as a use because it will cause the value to be dropped |
| /// again. [`write`] can be used to overwrite data without causing it to be |
| /// dropped. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// [`Copy`]: ../marker/trait.Copy.html |
| /// [`write`]: ../ptr/fn.write.html |
| /// |
| /// # Examples |
| /// |
| /// Manually remove the last item from a vector: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// use std::rc::Rc; |
| /// |
| /// let last = Rc::new(1); |
| /// let weak = Rc::downgrade(&last); |
| /// |
| /// let mut v = vec![Rc::new(0), last]; |
| /// |
| /// unsafe { |
| /// // Get a raw pointer to the last element in `v`. |
| /// let ptr = &mut v[1] as *mut _; |
| /// // Shorten `v` to prevent the last item from being dropped. We do that first, |
| /// // to prevent issues if the `drop_in_place` below panics. |
| /// v.set_len(1); |
| /// // Without a call `drop_in_place`, the last item would never be dropped, |
| /// // and the memory it manages would be leaked. |
| /// ptr::drop_in_place(ptr); |
| /// } |
| /// |
| /// assert_eq!(v, &[0.into()]); |
| /// |
| /// // Ensure that the last item was dropped. |
| /// assert!(weak.upgrade().is_none()); |
| /// ``` |
| /// |
| /// Unaligned values cannot be dropped in place, they must be copied to an aligned |
| /// location first: |
| /// ``` |
| /// use std::ptr; |
| /// use std::mem; |
| /// |
| /// unsafe fn drop_after_copy<T>(to_drop: *mut T) { |
| /// let mut copy: T = mem::uninitialized(); |
| /// ptr::copy(to_drop, &mut copy, 1); |
| /// drop(copy); |
| /// } |
| /// |
| /// #[repr(packed, C)] |
| /// struct Packed { |
| /// _padding: u8, |
| /// unaligned: Vec<i32>, |
| /// } |
| /// |
| /// let mut p = Packed { _padding: 0, unaligned: vec![42] }; |
| /// unsafe { |
| /// drop_after_copy(&mut p.unaligned as *mut _); |
| /// mem::forget(p); |
| /// } |
| /// ``` |
| /// |
| /// Notice that the compiler performs this copy automatically when dropping packed structs, |
| /// i.e., you do not usually have to worry about such issues unless you call `drop_in_place` |
| /// manually. |
| #[stable(feature = "drop_in_place", since = "1.8.0")] |
| #[inline(always)] |
| pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) { |
| real_drop_in_place(&mut *to_drop) |
| } |
| |
| // The real `drop_in_place` -- the one that gets called implicitly when variables go |
| // out of scope -- should have a safe reference and not a raw pointer as argument |
| // type. When we drop a local variable, we access it with a pointer that behaves |
| // like a safe reference; transmuting that to a raw pointer does not mean we can |
| // actually access it with raw pointers. |
| #[lang = "drop_in_place"] |
| #[allow(unconditional_recursion)] |
| unsafe fn real_drop_in_place<T: ?Sized>(to_drop: &mut T) { |
| // Code here does not matter - this is replaced by the |
| // real drop glue by the compiler. |
| real_drop_in_place(to_drop) |
| } |
| |
| /// Creates a null raw pointer. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let p: *const i32 = ptr::null(); |
| /// assert!(p.is_null()); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_promotable] |
| pub const fn null<T>() -> *const T { 0 as *const T } |
| |
| /// Creates a null mutable raw pointer. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let p: *mut i32 = ptr::null_mut(); |
| /// assert!(p.is_null()); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_promotable] |
| pub const fn null_mut<T>() -> *mut T { 0 as *mut T } |
| |
| /// Swaps the values at two mutable locations of the same type, without |
| /// deinitializing either. |
| /// |
| /// But for the following two exceptions, this function is semantically |
| /// equivalent to [`mem::swap`]: |
| /// |
| /// * It operates on raw pointers instead of references. When references are |
| /// available, [`mem::swap`] should be preferred. |
| /// |
| /// * The two pointed-to values may overlap. If the values do overlap, then the |
| /// overlapping region of memory from `x` will be used. This is demonstrated |
| /// in the second example below. |
| /// |
| /// [`mem::swap`]: ../mem/fn.swap.html |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * Both `x` and `y` must be [valid] for reads and writes. |
| /// |
| /// * Both `x` and `y` must be properly aligned. |
| /// |
| /// Note that even if `T` has size `0`, the pointers must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// |
| /// # Examples |
| /// |
| /// Swapping two non-overlapping regions: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let mut array = [0, 1, 2, 3]; |
| /// |
| /// let x = array[0..].as_mut_ptr() as *mut [u32; 2]; // this is `array[0..2]` |
| /// let y = array[2..].as_mut_ptr() as *mut [u32; 2]; // this is `array[2..4]` |
| /// |
| /// unsafe { |
| /// ptr::swap(x, y); |
| /// assert_eq!([2, 3, 0, 1], array); |
| /// } |
| /// ``` |
| /// |
| /// Swapping two overlapping regions: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let mut array = [0, 1, 2, 3]; |
| /// |
| /// let x = array[0..].as_mut_ptr() as *mut [u32; 3]; // this is `array[0..3]` |
| /// let y = array[1..].as_mut_ptr() as *mut [u32; 3]; // this is `array[1..4]` |
| /// |
| /// unsafe { |
| /// ptr::swap(x, y); |
| /// // The indices `1..3` of the slice overlap between `x` and `y`. |
| /// // Reasonable results would be for to them be `[2, 3]`, so that indices `0..3` are |
| /// // `[1, 2, 3]` (matching `y` before the `swap`); or for them to be `[0, 1]` |
| /// // so that indices `1..4` are `[0, 1, 2]` (matching `x` before the `swap`). |
| /// // This implementation is defined to make the latter choice. |
| /// assert_eq!([1, 0, 1, 2], array); |
| /// } |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub unsafe fn swap<T>(x: *mut T, y: *mut T) { |
| // Give ourselves some scratch space to work with. |
| // We do not have to worry about drops: `MaybeUninit` does nothing when dropped. |
| let mut tmp = MaybeUninit::<T>::uninitialized(); |
| |
| // Perform the swap |
| copy_nonoverlapping(x, tmp.as_mut_ptr(), 1); |
| copy(y, x, 1); // `x` and `y` may overlap |
| copy_nonoverlapping(tmp.get_ref(), y, 1); |
| } |
| |
| /// Swaps `count * size_of::<T>()` bytes between the two regions of memory |
| /// beginning at `x` and `y`. The two regions must *not* overlap. |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * Both `x` and `y` must be [valid] for reads and writes of `count * |
| /// size_of::<T>()` bytes. |
| /// |
| /// * Both `x` and `y` must be properly aligned. |
| /// |
| /// * The region of memory beginning at `x` with a size of `count * |
| /// size_of::<T>()` bytes must *not* overlap with the region of memory |
| /// beginning at `y` with the same size. |
| /// |
| /// Note that even if the effectively copied size (`count * size_of::<T>()`) is `0`, |
| /// the pointers must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let mut x = [1, 2, 3, 4]; |
| /// let mut y = [7, 8, 9]; |
| /// |
| /// unsafe { |
| /// ptr::swap_nonoverlapping(x.as_mut_ptr(), y.as_mut_ptr(), 2); |
| /// } |
| /// |
| /// assert_eq!(x, [7, 8, 3, 4]); |
| /// assert_eq!(y, [1, 2, 9]); |
| /// ``` |
| #[inline] |
| #[stable(feature = "swap_nonoverlapping", since = "1.27.0")] |
| pub unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) { |
| let x = x as *mut u8; |
| let y = y as *mut u8; |
| let len = mem::size_of::<T>() * count; |
| swap_nonoverlapping_bytes(x, y, len) |
| } |
| |
| #[inline] |
| pub(crate) unsafe fn swap_nonoverlapping_one<T>(x: *mut T, y: *mut T) { |
| // For types smaller than the block optimization below, |
| // just swap directly to avoid pessimizing codegen. |
| if mem::size_of::<T>() < 32 { |
| let z = read(x); |
| copy_nonoverlapping(y, x, 1); |
| write(y, z); |
| } else { |
| swap_nonoverlapping(x, y, 1); |
| } |
| } |
| |
| #[inline] |
| unsafe fn swap_nonoverlapping_bytes(x: *mut u8, y: *mut u8, len: usize) { |
| // The approach here is to utilize simd to swap x & y efficiently. Testing reveals |
| // that swapping either 32 bytes or 64 bytes at a time is most efficient for Intel |
| // Haswell E processors. LLVM is more able to optimize if we give a struct a |
| // #[repr(simd)], even if we don't actually use this struct directly. |
| // |
| // FIXME repr(simd) broken on emscripten and redox |
| // It's also broken on big-endian powerpc64 and s390x. #42778 |
| #[cfg_attr(not(any(target_os = "emscripten", target_os = "redox", |
| target_endian = "big")), |
| repr(simd))] |
| struct Block(u64, u64, u64, u64); |
| struct UnalignedBlock(u64, u64, u64, u64); |
| |
| let block_size = mem::size_of::<Block>(); |
| |
| // Loop through x & y, copying them `Block` at a time |
| // The optimizer should unroll the loop fully for most types |
| // N.B. We can't use a for loop as the `range` impl calls `mem::swap` recursively |
| let mut i = 0; |
| while i + block_size <= len { |
| // Create some uninitialized memory as scratch space |
| // Declaring `t` here avoids aligning the stack when this loop is unused |
| let mut t = mem::MaybeUninit::<Block>::uninitialized(); |
| let t = t.as_mut_ptr() as *mut u8; |
| let x = x.add(i); |
| let y = y.add(i); |
| |
| // Swap a block of bytes of x & y, using t as a temporary buffer |
| // This should be optimized into efficient SIMD operations where available |
| copy_nonoverlapping(x, t, block_size); |
| copy_nonoverlapping(y, x, block_size); |
| copy_nonoverlapping(t, y, block_size); |
| i += block_size; |
| } |
| |
| if i < len { |
| // Swap any remaining bytes |
| let mut t = mem::MaybeUninit::<UnalignedBlock>::uninitialized(); |
| let rem = len - i; |
| |
| let t = t.as_mut_ptr() as *mut u8; |
| let x = x.add(i); |
| let y = y.add(i); |
| |
| copy_nonoverlapping(x, t, rem); |
| copy_nonoverlapping(y, x, rem); |
| copy_nonoverlapping(t, y, rem); |
| } |
| } |
| |
| /// Moves `src` into the pointed `dst`, returning the previous `dst` value. |
| /// |
| /// Neither value is dropped. |
| /// |
| /// This function is semantically equivalent to [`mem::replace`] except that it |
| /// operates on raw pointers instead of references. When references are |
| /// available, [`mem::replace`] should be preferred. |
| /// |
| /// [`mem::replace`]: ../mem/fn.replace.html |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `dst` must be [valid] for writes. |
| /// |
| /// * `dst` must be properly aligned. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let mut rust = vec!['b', 'u', 's', 't']; |
| /// |
| /// // `mem::replace` would have the same effect without requiring the unsafe |
| /// // block. |
| /// let b = unsafe { |
| /// ptr::replace(&mut rust[0], 'r') |
| /// }; |
| /// |
| /// assert_eq!(b, 'b'); |
| /// assert_eq!(rust, &['r', 'u', 's', 't']); |
| /// ``` |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T { |
| mem::swap(&mut *dst, &mut src); // cannot overlap |
| src |
| } |
| |
| /// Reads the value from `src` without moving it. This leaves the |
| /// memory in `src` unchanged. |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `src` must be [valid] for reads. |
| /// |
| /// * `src` must be properly aligned. Use [`read_unaligned`] if this is not the |
| /// case. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let x = 12; |
| /// let y = &x as *const i32; |
| /// |
| /// unsafe { |
| /// assert_eq!(std::ptr::read(y), 12); |
| /// } |
| /// ``` |
| /// |
| /// Manually implement [`mem::swap`]: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// fn swap<T>(a: &mut T, b: &mut T) { |
| /// unsafe { |
| /// // Create a bitwise copy of the value at `a` in `tmp`. |
| /// let tmp = ptr::read(a); |
| /// |
| /// // Exiting at this point (either by explicitly returning or by |
| /// // calling a function which panics) would cause the value in `tmp` to |
| /// // be dropped while the same value is still referenced by `a`. This |
| /// // could trigger undefined behavior if `T` is not `Copy`. |
| /// |
| /// // Create a bitwise copy of the value at `b` in `a`. |
| /// // This is safe because mutable references cannot alias. |
| /// ptr::copy_nonoverlapping(b, a, 1); |
| /// |
| /// // As above, exiting here could trigger undefined behavior because |
| /// // the same value is referenced by `a` and `b`. |
| /// |
| /// // Move `tmp` into `b`. |
| /// ptr::write(b, tmp); |
| /// |
| /// // `tmp` has been moved (`write` takes ownership of its second argument), |
| /// // so nothing is dropped implicitly here. |
| /// } |
| /// } |
| /// |
| /// let mut foo = "foo".to_owned(); |
| /// let mut bar = "bar".to_owned(); |
| /// |
| /// swap(&mut foo, &mut bar); |
| /// |
| /// assert_eq!(foo, "bar"); |
| /// assert_eq!(bar, "foo"); |
| /// ``` |
| /// |
| /// ## Ownership of the Returned Value |
| /// |
| /// `read` creates a bitwise copy of `T`, regardless of whether `T` is [`Copy`]. |
| /// If `T` is not [`Copy`], using both the returned value and the value at |
| /// `*src` can violate memory safety. Note that assigning to `*src` counts as a |
| /// use because it will attempt to drop the value at `*src`. |
| /// |
| /// [`write`] can be used to overwrite data without causing it to be dropped. |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let mut s = String::from("foo"); |
| /// unsafe { |
| /// // `s2` now points to the same underlying memory as `s`. |
| /// let mut s2: String = ptr::read(&s); |
| /// |
| /// assert_eq!(s2, "foo"); |
| /// |
| /// // Assigning to `s2` causes its original value to be dropped. Beyond |
| /// // this point, `s` must no longer be used, as the underlying memory has |
| /// // been freed. |
| /// s2 = String::default(); |
| /// assert_eq!(s2, ""); |
| /// |
| /// // Assigning to `s` would cause the old value to be dropped again, |
| /// // resulting in undefined behavior. |
| /// // s = String::from("bar"); // ERROR |
| /// |
| /// // `ptr::write` can be used to overwrite a value without dropping it. |
| /// ptr::write(&mut s, String::from("bar")); |
| /// } |
| /// |
| /// assert_eq!(s, "bar"); |
| /// ``` |
| /// |
| /// [`mem::swap`]: ../mem/fn.swap.html |
| /// [valid]: ../ptr/index.html#safety |
| /// [`Copy`]: ../marker/trait.Copy.html |
| /// [`read_unaligned`]: ./fn.read_unaligned.html |
| /// [`write`]: ./fn.write.html |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub unsafe fn read<T>(src: *const T) -> T { |
| let mut tmp = MaybeUninit::<T>::uninitialized(); |
| copy_nonoverlapping(src, tmp.as_mut_ptr(), 1); |
| tmp.into_inner() |
| } |
| |
| /// Reads the value from `src` without moving it. This leaves the |
| /// memory in `src` unchanged. |
| /// |
| /// Unlike [`read`], `read_unaligned` works with unaligned pointers. |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `src` must be [valid] for reads. |
| /// |
| /// Like [`read`], `read_unaligned` creates a bitwise copy of `T`, regardless of |
| /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned |
| /// value and the value at `*src` can [violate memory safety][read-ownership]. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [`Copy`]: ../marker/trait.Copy.html |
| /// [`read`]: ./fn.read.html |
| /// [`write_unaligned`]: ./fn.write_unaligned.html |
| /// [read-ownership]: ./fn.read.html#ownership-of-the-returned-value |
| /// [valid]: ../ptr/index.html#safety |
| /// |
| /// # Examples |
| /// |
| /// Access members of a packed struct by reference: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// #[repr(packed, C)] |
| /// struct Packed { |
| /// _padding: u8, |
| /// unaligned: u32, |
| /// } |
| /// |
| /// let x = Packed { |
| /// _padding: 0x00, |
| /// unaligned: 0x01020304, |
| /// }; |
| /// |
| /// let v = unsafe { |
| /// // Take the address of a 32-bit integer which is not aligned. |
| /// // This must be done as a raw pointer; unaligned references are invalid. |
| /// let unaligned = &x.unaligned as *const u32; |
| /// |
| /// // Dereferencing normally will emit an aligned load instruction, |
| /// // causing undefined behavior. |
| /// // let v = *unaligned; // ERROR |
| /// |
| /// // Instead, use `read_unaligned` to read improperly aligned values. |
| /// let v = ptr::read_unaligned(unaligned); |
| /// |
| /// v |
| /// }; |
| /// |
| /// // Accessing unaligned values directly is safe. |
| /// assert!(x.unaligned == v); |
| /// ``` |
| #[inline] |
| #[stable(feature = "ptr_unaligned", since = "1.17.0")] |
| pub unsafe fn read_unaligned<T>(src: *const T) -> T { |
| let mut tmp = MaybeUninit::<T>::uninitialized(); |
| copy_nonoverlapping(src as *const u8, |
| tmp.as_mut_ptr() as *mut u8, |
| mem::size_of::<T>()); |
| tmp.into_inner() |
| } |
| |
| /// Overwrites a memory location with the given value without reading or |
| /// dropping the old value. |
| /// |
| /// `write` does not drop the contents of `dst`. This is safe, but it could leak |
| /// allocations or resources, so care should be taken not to overwrite an object |
| /// that should be dropped. |
| /// |
| /// Additionally, it does not drop `src`. Semantically, `src` is moved into the |
| /// location pointed to by `dst`. |
| /// |
| /// This is appropriate for initializing uninitialized memory, or overwriting |
| /// memory that has previously been [`read`] from. |
| /// |
| /// [`read`]: ./fn.read.html |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `dst` must be [valid] for writes. |
| /// |
| /// * `dst` must be properly aligned. Use [`write_unaligned`] if this is not the |
| /// case. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// [`write_unaligned`]: ./fn.write_unaligned.html |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let mut x = 0; |
| /// let y = &mut x as *mut i32; |
| /// let z = 12; |
| /// |
| /// unsafe { |
| /// std::ptr::write(y, z); |
| /// assert_eq!(std::ptr::read(y), 12); |
| /// } |
| /// ``` |
| /// |
| /// Manually implement [`mem::swap`]: |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// fn swap<T>(a: &mut T, b: &mut T) { |
| /// unsafe { |
| /// // Create a bitwise copy of the value at `a` in `tmp`. |
| /// let tmp = ptr::read(a); |
| /// |
| /// // Exiting at this point (either by explicitly returning or by |
| /// // calling a function which panics) would cause the value in `tmp` to |
| /// // be dropped while the same value is still referenced by `a`. This |
| /// // could trigger undefined behavior if `T` is not `Copy`. |
| /// |
| /// // Create a bitwise copy of the value at `b` in `a`. |
| /// // This is safe because mutable references cannot alias. |
| /// ptr::copy_nonoverlapping(b, a, 1); |
| /// |
| /// // As above, exiting here could trigger undefined behavior because |
| /// // the same value is referenced by `a` and `b`. |
| /// |
| /// // Move `tmp` into `b`. |
| /// ptr::write(b, tmp); |
| /// |
| /// // `tmp` has been moved (`write` takes ownership of its second argument), |
| /// // so nothing is dropped implicitly here. |
| /// } |
| /// } |
| /// |
| /// let mut foo = "foo".to_owned(); |
| /// let mut bar = "bar".to_owned(); |
| /// |
| /// swap(&mut foo, &mut bar); |
| /// |
| /// assert_eq!(foo, "bar"); |
| /// assert_eq!(bar, "foo"); |
| /// ``` |
| /// |
| /// [`mem::swap`]: ../mem/fn.swap.html |
| #[inline] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub unsafe fn write<T>(dst: *mut T, src: T) { |
| intrinsics::move_val_init(&mut *dst, src) |
| } |
| |
| /// Overwrites a memory location with the given value without reading or |
| /// dropping the old value. |
| /// |
| /// Unlike [`write`], the pointer may be unaligned. |
| /// |
| /// `write_unaligned` does not drop the contents of `dst`. This is safe, but it |
| /// could leak allocations or resources, so care should be taken not to overwrite |
| /// an object that should be dropped. |
| /// |
| /// Additionally, it does not drop `src`. Semantically, `src` is moved into the |
| /// location pointed to by `dst`. |
| /// |
| /// This is appropriate for initializing uninitialized memory, or overwriting |
| /// memory that has previously been read with [`read_unaligned`]. |
| /// |
| /// [`write`]: ./fn.write.html |
| /// [`read_unaligned`]: ./fn.read_unaligned.html |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `dst` must be [valid] for writes. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// |
| /// # Examples |
| /// |
| /// Access fields in a packed struct: |
| /// |
| /// ``` |
| /// use std::{mem, ptr}; |
| /// |
| /// #[repr(packed, C)] |
| /// #[derive(Default)] |
| /// struct Packed { |
| /// _padding: u8, |
| /// unaligned: u32, |
| /// } |
| /// |
| /// let v = 0x01020304; |
| /// let mut x: Packed = unsafe { mem::zeroed() }; |
| /// |
| /// unsafe { |
| /// // Take a reference to a 32-bit integer which is not aligned. |
| /// let unaligned = &mut x.unaligned as *mut u32; |
| /// |
| /// // Dereferencing normally will emit an aligned store instruction, |
| /// // causing undefined behavior because the pointer is not aligned. |
| /// // *unaligned = v; // ERROR |
| /// |
| /// // Instead, use `write_unaligned` to write improperly aligned values. |
| /// ptr::write_unaligned(unaligned, v); |
| /// } |
| /// |
| /// // Accessing unaligned values directly is safe. |
| /// assert!(x.unaligned == v); |
| /// ``` |
| #[inline] |
| #[stable(feature = "ptr_unaligned", since = "1.17.0")] |
| pub unsafe fn write_unaligned<T>(dst: *mut T, src: T) { |
| copy_nonoverlapping(&src as *const T as *const u8, |
| dst as *mut u8, |
| mem::size_of::<T>()); |
| mem::forget(src); |
| } |
| |
| /// Performs a volatile read of the value from `src` without moving it. This |
| /// leaves the memory in `src` 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. |
| /// |
| /// Memory accessed with `read_volatile` or [`write_volatile`] should not be |
| /// accessed with non-volatile operations. |
| /// |
| /// [`write_volatile`]: ./fn.write_volatile.html |
| /// |
| /// # Notes |
| /// |
| /// Rust does not currently have a rigorously and formally defined memory model, |
| /// so the precise semantics of what "volatile" means here is subject to change |
| /// over time. That being said, the semantics will almost always end up pretty |
| /// similar to [C11's definition of volatile][c11]. |
| /// |
| /// The compiler shouldn't change the relative order or number of volatile |
| /// memory operations. However, volatile memory operations on zero-sized types |
| /// (e.g. if a zero-sized type is passed to `read_volatile`) are no-ops |
| /// and may be ignored. |
| /// |
| /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `src` must be [valid] for reads. |
| /// |
| /// * `src` must be properly aligned. |
| /// |
| /// Like [`read`], `read_unaligned` creates a bitwise copy of `T`, regardless of |
| /// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned |
| /// value and the value at `*src` can [violate memory safety][read-ownership]. |
| /// However, storing non-[`Copy`] types in volatile memory is almost certainly |
| /// incorrect. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// [`Copy`]: ../marker/trait.Copy.html |
| /// [`read`]: ./fn.read.html |
| /// |
| /// Just like in C, whether an operation is volatile has no bearing whatsoever |
| /// on questions involving concurrent access from multiple threads. Volatile |
| /// accesses behave exactly like non-atomic accesses in that regard. In particular, |
| /// a race between a `read_volatile` and any write operation to the same location |
| /// is undefined behavior. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let x = 12; |
| /// let y = &x as *const i32; |
| /// |
| /// unsafe { |
| /// assert_eq!(std::ptr::read_volatile(y), 12); |
| /// } |
| /// ``` |
| #[inline] |
| #[stable(feature = "volatile", since = "1.9.0")] |
| pub unsafe fn read_volatile<T>(src: *const T) -> T { |
| intrinsics::volatile_load(src) |
| } |
| |
| /// Performs a volatile write of a memory location with the given value without |
| /// reading or dropping the old value. |
| /// |
| /// 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. |
| /// |
| /// Memory accessed with [`read_volatile`] or `write_volatile` should not be |
| /// accessed with non-volatile operations. |
| /// |
| /// `write_volatile` does not drop the contents of `dst`. This is safe, but it |
| /// could leak allocations or resources, so care should be taken not to overwrite |
| /// an object that should be dropped. |
| /// |
| /// Additionally, it does not drop `src`. Semantically, `src` is moved into the |
| /// location pointed to by `dst`. |
| /// |
| /// [`read_volatile`]: ./fn.read_volatile.html |
| /// |
| /// # Notes |
| /// |
| /// Rust does not currently have a rigorously and formally defined memory model, |
| /// so the precise semantics of what "volatile" means here is subject to change |
| /// over time. That being said, the semantics will almost always end up pretty |
| /// similar to [C11's definition of volatile][c11]. |
| /// |
| /// The compiler shouldn't change the relative order or number of volatile |
| /// memory operations. However, volatile memory operations on zero-sized types |
| /// (e.g. if a zero-sized type is passed to `write_volatile`) are no-ops |
| /// and may be ignored. |
| /// |
| /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf |
| /// |
| /// # Safety |
| /// |
| /// Behavior is undefined if any of the following conditions are violated: |
| /// |
| /// * `dst` must be [valid] for writes. |
| /// |
| /// * `dst` must be properly aligned. |
| /// |
| /// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned. |
| /// |
| /// [valid]: ../ptr/index.html#safety |
| /// |
| /// Just like in C, whether an operation is volatile has no bearing whatsoever |
| /// on questions involving concurrent access from multiple threads. Volatile |
| /// accesses behave exactly like non-atomic accesses in that regard. In particular, |
| /// a race between a `write_volatile` and any other operation (reading or writing) |
| /// on the same location is undefined behavior. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let mut x = 0; |
| /// let y = &mut x as *mut i32; |
| /// let z = 12; |
| /// |
| /// unsafe { |
| /// std::ptr::write_volatile(y, z); |
| /// assert_eq!(std::ptr::read_volatile(y), 12); |
| /// } |
| /// ``` |
| #[inline] |
| #[stable(feature = "volatile", since = "1.9.0")] |
| pub unsafe fn write_volatile<T>(dst: *mut T, src: T) { |
| intrinsics::volatile_store(dst, src); |
| } |
| |
| #[lang = "const_ptr"] |
| 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. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let s: &str = "Follow the rabbit"; |
| /// let ptr: *const u8 = s.as_ptr(); |
| /// assert!(!ptr.is_null()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn is_null(self) -> bool { |
| // Compare via a cast to a thin pointer, so fat pointers are only |
| // considering their "data" part for null-ness. |
| (self as *const u8) == null() |
| } |
| |
| /// Returns `None` if the pointer is null, or else returns a reference to |
| /// the value wrapped in `Some`. |
| /// |
| /// # Safety |
| /// |
| /// While this method and its mutable counterpart are useful for |
| /// null-safety, it is important to note that this is still an unsafe |
| /// operation because the returned value could be pointing to invalid |
| /// memory. |
| /// |
| /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does |
| /// not necessarily reflect the actual lifetime of the data. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// 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")] |
| #[inline] |
| pub unsafe fn as_ref<'a>(self) -> Option<&'a T> { |
| if self.is_null() { |
| None |
| } else { |
| Some(&*self) |
| } |
| } |
| |
| /// 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: |
| /// |
| /// * 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, **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. |
| /// |
| /// # 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")] |
| #[inline] |
| pub unsafe fn offset(self, count: isize) -> *const T where T: Sized { |
| intrinsics::offset(self, count) |
| } |
| |
| /// 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 |
| /// |
| /// The resulting pointer does not need to be in bounds, but it is |
| /// potentially hazardous to dereference (which requires `unsafe`). |
| /// In particular, the resulting pointer may *not* be used to access a |
| /// different allocated object than the one `self` points to. In other |
| /// words, `x.wrapping_offset(y.wrapping_offset_from(x))` is |
| /// *not* the same as `y`, and dereferencing it is undefined behavior |
| /// unless `x` and `y` point into the same allocated object. |
| /// |
| /// Always use `.offset(count)` instead when possible, because `offset` |
| /// allows the compiler to optimize better. If you need to cross object |
| /// boundaries, cast the pointer to an integer and do the arithmetic there. |
| /// |
| /// # 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")] |
| #[inline] |
| pub fn wrapping_offset(self, count: isize) -> *const T where T: Sized { |
| unsafe { |
| intrinsics::arith_offset(self, count) |
| } |
| } |
| |
| /// Calculates the distance between two pointers. The returned value is in |
| /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`. |
| /// |
| /// This function is the inverse of [`offset`]. |
| /// |
| /// [`offset`]: #method.offset |
| /// [`wrapping_offset_from`]: #method.wrapping_offset_from |
| /// |
| /// # 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. |
| /// |
| /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`. |
| /// |
| /// * The distance between the pointers, in bytes, must be an exact multiple |
| /// of the size of `T`. |
| /// |
| /// * The distance being in bounds cannot rely on "wrapping around" the address space. |
| /// |
| /// The compiler and standard library generally try 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 |
| /// `ptr_into_vec.offset_from(vec.as_ptr())` 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_from`] instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a Zero-Sized Type ("ZST"). |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(ptr_offset_from)] |
| /// |
| /// 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); |
| /// } |
| /// ``` |
| #[unstable(feature = "ptr_offset_from", issue = "41079")] |
| #[inline] |
| pub 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_value() as usize); |
| |
| // This is the same sequence that Clang emits for pointer subtraction. |
| // It can be neither `nsw` nor `nuw` because the input is treated as |
| // unsigned but then the output is treated as signed, so neither works. |
| let d = isize::wrapping_sub(self as _, origin as _); |
| intrinsics::exact_div(d, pointee_size as _) |
| } |
| |
| /// Calculates the distance between two pointers. The returned value is in |
| /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`. |
| /// |
| /// If the address different between the two pointers is not a multiple of |
| /// `mem::size_of::<T>()` then the result of the division is rounded towards |
| /// zero. |
| /// |
| /// Though this method is safe for any two pointers, note that its result |
| /// will be mostly useless if the two pointers aren't into the same allocated |
| /// object, for example if they point to two different local variables. |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a zero-sized type. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(ptr_wrapping_offset_from)] |
| /// |
| /// let a = [0; 5]; |
| /// let ptr1: *const i32 = &a[1]; |
| /// let ptr2: *const i32 = &a[3]; |
| /// assert_eq!(ptr2.wrapping_offset_from(ptr1), 2); |
| /// assert_eq!(ptr1.wrapping_offset_from(ptr2), -2); |
| /// assert_eq!(ptr1.wrapping_offset(2), ptr2); |
| /// assert_eq!(ptr2.wrapping_offset(-2), ptr1); |
| /// |
| /// let ptr1: *const i32 = 3 as _; |
| /// let ptr2: *const i32 = 13 as _; |
| /// assert_eq!(ptr2.wrapping_offset_from(ptr1), 2); |
| /// ``` |
| #[unstable(feature = "ptr_wrapping_offset_from", issue = "41079")] |
| #[inline] |
| pub fn wrapping_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_value() as usize); |
| |
| let d = isize::wrapping_sub(self as _, origin as _); |
| d.wrapping_div(pointee_size as _) |
| } |
| |
| /// 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_offset` instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// # 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")] |
| #[inline] |
| pub unsafe fn add(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.offset(count as isize) |
| } |
| |
| /// 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_offset` instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// # 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")] |
| #[inline] |
| pub unsafe fn sub(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.offset((count as isize).wrapping_neg()) |
| } |
| |
| /// 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 |
| /// |
| /// The resulting pointer does not need to be in bounds, but it is |
| /// potentially hazardous to dereference (which requires `unsafe`). |
| /// |
| /// Always use `.add(count)` instead when possible, because `add` |
| /// allows the compiler to optimize better. |
| /// |
| /// # 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")] |
| #[inline] |
| pub fn wrapping_add(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.wrapping_offset(count as isize) |
| } |
| |
| /// Calculates the offset from a pointer using wrapping arithmetic. |
| /// (convenience for `.wrapping_offset((count as isize).wrapping_sub())`) |
| /// |
| /// `count` is in units of T; e.g. a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// The resulting pointer does not need to be in bounds, but it is |
| /// potentially hazardous to dereference (which requires `unsafe`). |
| /// |
| /// Always use `.sub(count)` instead when possible, because `sub` |
| /// allows the compiler to optimize better. |
| /// |
| /// # 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")] |
| #[inline] |
| pub fn wrapping_sub(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.wrapping_offset((count as isize).wrapping_neg()) |
| } |
| |
| /// 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`]: ./ptr/fn.read.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn read(self) -> T |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.read_volatile.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn read_volatile(self) -> T |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.read_unaligned.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn read_unaligned(self) -> T |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.copy.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn copy_to(self, dest: *mut T, count: usize) |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.copy_nonoverlapping.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize) |
| where T: Sized, |
| { |
| 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_value()`. |
| /// |
| /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be |
| /// used with the `offset` or `offset_to` methods. |
| /// |
| /// There are no guarantees whatsover 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` |
| /// |
| /// ``` |
| /// # #![feature(align_offset)] |
| /// # fn foo(n: usize) { |
| /// # use std::mem::align_of; |
| /// # unsafe { |
| /// let x = [5u8, 6u8, 7u8, 8u8, 9u8]; |
| /// let ptr = &x[n] as *const u8; |
| /// let offset = ptr.align_offset(align_of::<u16>()); |
| /// if offset < x.len() - n - 1 { |
| /// let u16_ptr = ptr.add(offset) as *const u16; |
| /// assert_ne!(*u16_ptr, 500); |
| /// } else { |
| /// // while the pointer can be aligned via `offset`, it would point |
| /// // outside the allocation |
| /// } |
| /// # } } |
| /// ``` |
| #[unstable(feature = "align_offset", issue = "44488")] |
| pub 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"); |
| } |
| unsafe { |
| align_offset(self, align) |
| } |
| } |
| } |
| |
| |
| #[lang = "mut_ptr"] |
| impl<T: ?Sized> *mut 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. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let mut s = [1, 2, 3]; |
| /// let ptr: *mut u32 = s.as_mut_ptr(); |
| /// assert!(!ptr.is_null()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn is_null(self) -> bool { |
| // Compare via a cast to a thin pointer, so fat pointers are only |
| // considering their "data" part for null-ness. |
| (self as *mut u8) == null_mut() |
| } |
| |
| /// Returns `None` if the pointer is null, or else returns a reference to |
| /// the value wrapped in `Some`. |
| /// |
| /// # Safety |
| /// |
| /// While this method and its mutable counterpart are useful for |
| /// null-safety, it is important to note that this is still an unsafe |
| /// operation because the returned value could be pointing to invalid |
| /// memory. |
| /// |
| /// Additionally, the lifetime `'a` returned is arbitrarily chosen and does |
| /// not necessarily reflect the actual lifetime of the data. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let ptr: *mut u8 = &mut 10u8 as *mut 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: *mut u8 = &mut 10u8 as *mut u8; |
| /// |
| /// unsafe { |
| /// let val_back = &*ptr; |
| /// println!("We got back the value: {}!", val_back); |
| /// } |
| /// ``` |
| #[stable(feature = "ptr_as_ref", since = "1.9.0")] |
| #[inline] |
| pub unsafe fn as_ref<'a>(self) -> Option<&'a T> { |
| if self.is_null() { |
| None |
| } else { |
| Some(&*self) |
| } |
| } |
| |
| /// 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: |
| /// |
| /// * 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, **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. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let mut s = [1, 2, 3]; |
| /// let ptr: *mut u32 = s.as_mut_ptr(); |
| /// |
| /// unsafe { |
| /// println!("{}", *ptr.offset(1)); |
| /// println!("{}", *ptr.offset(2)); |
| /// } |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub unsafe fn offset(self, count: isize) -> *mut T where T: Sized { |
| intrinsics::offset(self, count) as *mut T |
| } |
| |
| /// 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 |
| /// |
| /// The resulting pointer does not need to be in bounds, but it is |
| /// potentially hazardous to dereference (which requires `unsafe`). |
| /// In particular, the resulting pointer may *not* be used to access a |
| /// different allocated object than the one `self` points to. In other |
| /// words, `x.wrapping_offset(y.wrapping_offset_from(x))` is |
| /// *not* the same as `y`, and dereferencing it is undefined behavior |
| /// unless `x` and `y` point into the same allocated object. |
| /// |
| /// Always use `.offset(count)` instead when possible, because `offset` |
| /// allows the compiler to optimize better. If you need to cross object |
| /// boundaries, cast the pointer to an integer and do the arithmetic there. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// // Iterate using a raw pointer in increments of two elements |
| /// let mut data = [1u8, 2, 3, 4, 5]; |
| /// let mut ptr: *mut u8 = data.as_mut_ptr(); |
| /// let step = 2; |
| /// let end_rounded_up = ptr.wrapping_offset(6); |
| /// |
| /// while ptr != end_rounded_up { |
| /// unsafe { |
| /// *ptr = 0; |
| /// } |
| /// ptr = ptr.wrapping_offset(step); |
| /// } |
| /// assert_eq!(&data, &[0, 2, 0, 4, 0]); |
| /// ``` |
| #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")] |
| #[inline] |
| pub fn wrapping_offset(self, count: isize) -> *mut T where T: Sized { |
| unsafe { |
| intrinsics::arith_offset(self, count) as *mut T |
| } |
| } |
| |
| /// Returns `None` if the pointer is null, or else returns a mutable |
| /// reference to the value wrapped in `Some`. |
| /// |
| /// # Safety |
| /// |
| /// As with `as_ref`, this is unsafe because it cannot verify the validity |
| /// of the returned pointer, nor can it ensure that the lifetime `'a` |
| /// returned is indeed a valid lifetime for the contained data. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// let mut s = [1, 2, 3]; |
| /// let ptr: *mut u32 = s.as_mut_ptr(); |
| /// let first_value = unsafe { ptr.as_mut().unwrap() }; |
| /// *first_value = 4; |
| /// println!("{:?}", s); // It'll print: "[4, 2, 3]". |
| /// ``` |
| #[stable(feature = "ptr_as_ref", since = "1.9.0")] |
| #[inline] |
| pub unsafe fn as_mut<'a>(self) -> Option<&'a mut T> { |
| if self.is_null() { |
| None |
| } else { |
| Some(&mut *self) |
| } |
| } |
| |
| /// Calculates the distance between two pointers. The returned value is in |
| /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`. |
| /// |
| /// This function is the inverse of [`offset`]. |
| /// |
| /// [`offset`]: #method.offset-1 |
| /// [`wrapping_offset_from`]: #method.wrapping_offset_from-1 |
| /// |
| /// # 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. |
| /// |
| /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`. |
| /// |
| /// * The distance between the pointers, in bytes, must be an exact multiple |
| /// of the size of `T`. |
| /// |
| /// * The distance being in bounds cannot rely on "wrapping around" the address space. |
| /// |
| /// The compiler and standard library generally try 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 |
| /// `ptr_into_vec.offset_from(vec.as_ptr())` 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_from`] instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a Zero-Sized Type ("ZST"). |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(ptr_offset_from)] |
| /// |
| /// let mut a = [0; 5]; |
| /// let ptr1: *mut i32 = &mut a[1]; |
| /// let ptr2: *mut i32 = &mut 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); |
| /// } |
| /// ``` |
| #[unstable(feature = "ptr_offset_from", issue = "41079")] |
| #[inline] |
| pub unsafe fn offset_from(self, origin: *const T) -> isize where T: Sized { |
| (self as *const T).offset_from(origin) |
| } |
| |
| /// Calculates the distance between two pointers. The returned value is in |
| /// units of T: the distance in bytes is divided by `mem::size_of::<T>()`. |
| /// |
| /// If the address different between the two pointers is not a multiple of |
| /// `mem::size_of::<T>()` then the result of the division is rounded towards |
| /// zero. |
| /// |
| /// Though this method is safe for any two pointers, note that its result |
| /// will be mostly useless if the two pointers aren't into the same allocated |
| /// object, for example if they point to two different local variables. |
| /// |
| /// # Panics |
| /// |
| /// This function panics if `T` is a zero-sized type. |
| /// |
| /// # Examples |
| /// |
| /// Basic usage: |
| /// |
| /// ``` |
| /// #![feature(ptr_wrapping_offset_from)] |
| /// |
| /// let mut a = [0; 5]; |
| /// let ptr1: *mut i32 = &mut a[1]; |
| /// let ptr2: *mut i32 = &mut a[3]; |
| /// assert_eq!(ptr2.wrapping_offset_from(ptr1), 2); |
| /// assert_eq!(ptr1.wrapping_offset_from(ptr2), -2); |
| /// assert_eq!(ptr1.wrapping_offset(2), ptr2); |
| /// assert_eq!(ptr2.wrapping_offset(-2), ptr1); |
| /// |
| /// let ptr1: *mut i32 = 3 as _; |
| /// let ptr2: *mut i32 = 13 as _; |
| /// assert_eq!(ptr2.wrapping_offset_from(ptr1), 2); |
| /// ``` |
| #[unstable(feature = "ptr_wrapping_offset_from", issue = "41079")] |
| #[inline] |
| pub fn wrapping_offset_from(self, origin: *const T) -> isize where T: Sized { |
| (self as *const T).wrapping_offset_from(origin) |
| } |
| |
| /// 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_offset` instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// # 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")] |
| #[inline] |
| pub unsafe fn add(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.offset(count as isize) |
| } |
| |
| /// 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_offset` instead if these constraints are |
| /// difficult to satisfy. The only advantage of this method is that it |
| /// enables more aggressive compiler optimizations. |
| /// |
| /// # 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")] |
| #[inline] |
| pub unsafe fn sub(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.offset((count as isize).wrapping_neg()) |
| } |
| |
| /// 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 |
| /// |
| /// The resulting pointer does not need to be in bounds, but it is |
| /// potentially hazardous to dereference (which requires `unsafe`). |
| /// |
| /// Always use `.add(count)` instead when possible, because `add` |
| /// allows the compiler to optimize better. |
| /// |
| /// # 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")] |
| #[inline] |
| pub fn wrapping_add(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.wrapping_offset(count as isize) |
| } |
| |
| /// Calculates the offset from a pointer using wrapping arithmetic. |
| /// (convenience for `.wrapping_offset((count as isize).wrapping_sub())`) |
| /// |
| /// `count` is in units of T; e.g. a `count` of 3 represents a pointer |
| /// offset of `3 * size_of::<T>()` bytes. |
| /// |
| /// # Safety |
| /// |
| /// The resulting pointer does not need to be in bounds, but it is |
| /// potentially hazardous to dereference (which requires `unsafe`). |
| /// |
| /// Always use `.sub(count)` instead when possible, because `sub` |
| /// allows the compiler to optimize better. |
| /// |
| /// # 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")] |
| #[inline] |
| pub fn wrapping_sub(self, count: usize) -> Self |
| where T: Sized, |
| { |
| self.wrapping_offset((count as isize).wrapping_neg()) |
| } |
| |
| /// 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`]: ./ptr/fn.read.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn read(self) -> T |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.read_volatile.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn read_volatile(self) -> T |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.read_unaligned.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn read_unaligned(self) -> T |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.copy.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn copy_to(self, dest: *mut T, count: usize) |
| where T: Sized, |
| { |
| 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`]: ./ptr/fn.copy_nonoverlapping.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn copy_to_nonoverlapping(self, dest: *mut T, count: usize) |
| where T: Sized, |
| { |
| copy_nonoverlapping(self, dest, count) |
| } |
| |
| /// Copies `count * size_of<T>` bytes from `src` to `self`. The source |
| /// and destination may overlap. |
| /// |
| /// NOTE: this has the *opposite* argument order of [`ptr::copy`]. |
| /// |
| /// See [`ptr::copy`] for safety concerns and examples. |
| /// |
| /// [`ptr::copy`]: ./ptr/fn.copy.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn copy_from(self, src: *const T, count: usize) |
| where T: Sized, |
| { |
| copy(src, self, count) |
| } |
| |
| /// Copies `count * size_of<T>` bytes from `src` to `self`. The source |
| /// and destination may *not* overlap. |
| /// |
| /// NOTE: this has the *opposite* argument order of [`ptr::copy_nonoverlapping`]. |
| /// |
| /// See [`ptr::copy_nonoverlapping`] for safety concerns and examples. |
| /// |
| /// [`ptr::copy_nonoverlapping`]: ./ptr/fn.copy_nonoverlapping.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn copy_from_nonoverlapping(self, src: *const T, count: usize) |
| where T: Sized, |
| { |
| copy_nonoverlapping(src, self, count) |
| } |
| |
| /// Executes the destructor (if any) of the pointed-to value. |
| /// |
| /// See [`ptr::drop_in_place`] for safety concerns and examples. |
| /// |
| /// [`ptr::drop_in_place`]: ./ptr/fn.drop_in_place.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn drop_in_place(self) { |
| drop_in_place(self) |
| } |
| |
| /// Overwrites a memory location with the given value without reading or |
| /// dropping the old value. |
| /// |
| /// See [`ptr::write`] for safety concerns and examples. |
| /// |
| /// [`ptr::write`]: ./ptr/fn.write.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn write(self, val: T) |
| where T: Sized, |
| { |
| write(self, val) |
| } |
| |
| /// Invokes memset on the specified pointer, setting `count * size_of::<T>()` |
| /// bytes of memory starting at `self` to `val`. |
| /// |
| /// See [`ptr::write_bytes`] for safety concerns and examples. |
| /// |
| /// [`ptr::write_bytes`]: ./ptr/fn.write_bytes.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn write_bytes(self, val: u8, count: usize) |
| where T: Sized, |
| { |
| write_bytes(self, val, count) |
| } |
| |
| /// Performs a volatile write of a memory location with the given value without |
| /// reading or dropping the old value. |
| /// |
| /// 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::write_volatile`] for safety concerns and examples. |
| /// |
| /// [`ptr::write_volatile`]: ./ptr/fn.write_volatile.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn write_volatile(self, val: T) |
| where T: Sized, |
| { |
| write_volatile(self, val) |
| } |
| |
| /// Overwrites a memory location with the given value without reading or |
| /// dropping the old value. |
| /// |
| /// Unlike `write`, the pointer may be unaligned. |
| /// |
| /// See [`ptr::write_unaligned`] for safety concerns and examples. |
| /// |
| /// [`ptr::write_unaligned`]: ./ptr/fn.write_unaligned.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn write_unaligned(self, val: T) |
| where T: Sized, |
| { |
| write_unaligned(self, val) |
| } |
| |
| /// Replaces the value at `self` with `src`, returning the old |
| /// value, without dropping either. |
| /// |
| /// See [`ptr::replace`] for safety concerns and examples. |
| /// |
| /// [`ptr::replace`]: ./ptr/fn.replace.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn replace(self, src: T) -> T |
| where T: Sized, |
| { |
| replace(self, src) |
| } |
| |
| /// Swaps the values at two mutable locations of the same type, without |
| /// deinitializing either. They may overlap, unlike `mem::swap` which is |
| /// otherwise equivalent. |
| /// |
| /// See [`ptr::swap`] for safety concerns and examples. |
| /// |
| /// [`ptr::swap`]: ./ptr/fn.swap.html |
| #[stable(feature = "pointer_methods", since = "1.26.0")] |
| #[inline] |
| pub unsafe fn swap(self, with: *mut T) |
| where T: Sized, |
| { |
| swap(self, with) |
| } |
| |
| /// 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_value()`. |
| /// |
| /// The offset is expressed in number of `T` elements, and not bytes. The value returned can be |
| /// used with the `offset` or `offset_to` methods. |
| /// |
| /// There are no guarantees whatsover 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` |
| /// |
| /// ``` |
| /// # #![feature(align_offset)] |
| /// # fn foo(n: usize) { |
| /// # use std::mem::align_of; |
| /// # unsafe { |
| /// let x = [5u8, 6u8, 7u8, 8u8, 9u8]; |
| /// let ptr = &x[n] as *const u8; |
| /// let offset = ptr.align_offset(align_of::<u16>()); |
| /// if offset < x.len() - n - 1 { |
| /// let u16_ptr = ptr.add(offset) as *const u16; |
| /// assert_ne!(*u16_ptr, 500); |
| /// } else { |
| /// // while the pointer can be aligned via `offset`, it would point |
| /// // outside the allocation |
| /// } |
| /// # } } |
| /// ``` |
| #[unstable(feature = "align_offset", issue = "44488")] |
| pub 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"); |
| } |
| unsafe { |
| align_offset(self, align) |
| } |
| } |
| } |
| |
| /// Align pointer `p`. |
| /// |
| /// Calculate offset (in terms of elements of `stride` stride) that has to be applied |
| /// to pointer `p` so that pointer `p` would get aligned to `a`. |
| /// |
| /// Note: This implementation has been carefully tailored to not panic. It is UB for this to panic. |
| /// The only real change that can be made here is change of `INV_TABLE_MOD_16` and associated |
| /// constants. |
| /// |
| /// If we ever decide to make it possible to call the intrinsic with `a` that is not a |
| /// power-of-two, it will probably be more prudent to just change to a naive implementation rather |
| /// than trying to adapt this to accommodate that change. |
| /// |
| /// Any questions go to @nagisa. |
| #[lang="align_offset"] |
| pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize { |
| /// Calculate multiplicative modular inverse of `x` modulo `m`. |
| /// |
| /// This implementation is tailored for align_offset and has following preconditions: |
| /// |
| /// * `m` is a power-of-two; |
| /// * `x < m`; (if `x ≥ m`, pass in `x % m` instead) |
| /// |
| /// Implementation of this function shall not panic. Ever. |
| #[inline] |
| fn mod_inv(x: usize, m: usize) -> usize { |
| /// Multiplicative modular inverse table modulo 2⁴ = 16. |
| /// |
| /// Note, that this table does not contain values where inverse does not exist (i.e. for |
| /// `0⁻¹ mod 16`, `2⁻¹ mod 16`, etc.) |
| const INV_TABLE_MOD_16: [u8; 8] = [1, 11, 13, 7, 9, 3, 5, 15]; |
| /// Modulo for which the `INV_TABLE_MOD_16` is intended. |
| const INV_TABLE_MOD: usize = 16; |
| /// INV_TABLE_MOD² |
| const INV_TABLE_MOD_SQUARED: usize = INV_TABLE_MOD * INV_TABLE_MOD; |
| |
| let table_inverse = INV_TABLE_MOD_16[(x & (INV_TABLE_MOD - 1)) >> 1] as usize; |
| if m <= INV_TABLE_MOD { |
| table_inverse & (m - 1) |
| } else { |
| // We iterate "up" using the following formula: |
| // |
| // $$ xy ≡ 1 (mod 2ⁿ) → xy (2 - xy) ≡ 1 (mod 2²ⁿ) $$ |
| // |
| // until 2²ⁿ ≥ m. Then we can reduce to our desired `m` by taking the result `mod m`. |
| let mut inverse = table_inverse; |
| let mut going_mod = INV_TABLE_MOD_SQUARED; |
| loop { |
| // y = y * (2 - xy) mod n |
| // |
| // Note, that we use wrapping operations here intentionally – the original formula |
| // uses e.g. subtraction `mod n`. It is entirely fine to do them `mod |
| // usize::max_value()` instead, because we take the result `mod n` at the end |
| // anyway. |
| inverse = inverse.wrapping_mul( |
| 2usize.wrapping_sub(x.wrapping_mul(inverse)) |
| ) & (going_mod - 1); |
| if going_mod > m { |
| return inverse & (m - 1); |
| } |
| going_mod = going_mod.wrapping_mul(going_mod); |
| } |
| } |
| } |
| |
| let stride = ::mem::size_of::<T>(); |
| let a_minus_one = a.wrapping_sub(1); |
| let pmoda = p as usize & a_minus_one; |
| |
| if pmoda == 0 { |
| // Already aligned. Yay! |
| return 0; |
| } |
| |
| if stride <= 1 { |
| return if stride == 0 { |
| // If the pointer is not aligned, and the element is zero-sized, then no amount of |
| // elements will ever align the pointer. |
| !0 |
| } else { |
| a.wrapping_sub(pmoda) |
| }; |
| } |
| |
| let smoda = stride & a_minus_one; |
| // a is power-of-two so cannot be 0. stride = 0 is handled above. |
| let gcdpow = intrinsics::cttz_nonzero(stride).min(intrinsics::cttz_nonzero(a)); |
| let gcd = 1usize << gcdpow; |
| |
| if p as usize & (gcd - 1) == 0 { |
| // This branch solves for the following linear congruence equation: |
| // |
| // $$ p + so ≡ 0 mod a $$ |
| // |
| // $p$ here is the pointer value, $s$ – stride of `T`, $o$ offset in `T`s, and $a$ – the |
| // requested alignment. |
| // |
| // g = gcd(a, s) |
| // o = (a - (p mod a))/g * ((s/g)⁻¹ mod a) |
| // |
| // The first term is “the relative alignment of p to a”, the second term is “how does |
| // incrementing p by s bytes change the relative alignment of p”. Division by `g` is |
| // necessary to make this equation well formed if $a$ and $s$ are not co-prime. |
| // |
| // Furthermore, the result produced by this solution is not “minimal”, so it is necessary |
| // to take the result $o mod lcm(s, a)$. We can replace $lcm(s, a)$ with just a $a / g$. |
| let j = a.wrapping_sub(pmoda) >> gcdpow; |
| let k = smoda >> gcdpow; |
| return intrinsics::unchecked_rem(j.wrapping_mul(mod_inv(k, a)), a >> gcdpow); |
| } |
| |
| // Cannot be aligned at all. |
| usize::max_value() |
| } |
| |
| |
| |
| // 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 {} |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> PartialEq for *mut T { |
| #[inline] |
| fn eq(&self, other: &*mut T) -> bool { *self == *other } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> Eq for *mut T {} |
| |
| /// Compare raw pointers for equality. |
| /// |
| /// This is the same as using the `==` operator, but less generic: |
| /// the arguments have to be `*const T` raw pointers, |
| /// not anything that implements `PartialEq`. |
| /// |
| /// This can be used to compare `&T` references (which coerce to `*const T` implicitly) |
| /// by their address rather than comparing the values they point to |
| /// (which is what the `PartialEq for &T` implementation does). |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::ptr; |
| /// |
| /// let five = 5; |
| /// let other_five = 5; |
| /// let five_ref = &five; |
| /// let same_five_ref = &five; |
| /// let other_five_ref = &other_five; |
| /// |
| /// assert!(five_ref == same_five_ref); |
| /// assert!(five_ref == other_five_ref); |
| /// |
| /// assert!(ptr::eq(five_ref, same_five_ref)); |
| /// assert!(!ptr::eq(five_ref, other_five_ref)); |
| /// ``` |
| #[stable(feature = "ptr_eq", since = "1.17.0")] |
| #[inline] |
| pub fn eq<T: ?Sized>(a: *const T, b: *const T) -> bool { |
| a == b |
| } |
| |
| // Impls for function pointers |
| macro_rules! fnptr_impls_safety_abi { |
| ($FnTy: ty, $($Arg: ident),*) => { |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> PartialEq for $FnTy { |
| #[inline] |
| fn eq(&self, other: &Self) -> bool { |
| *self as usize == *other as usize |
| } |
| } |
| |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> Eq for $FnTy {} |
| |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> PartialOrd for $FnTy { |
| #[inline] |
| fn partial_cmp(&self, other: &Self) -> Option<Ordering> { |
| (*self as usize).partial_cmp(&(*other as usize)) |
| } |
| } |
| |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> Ord for $FnTy { |
| #[inline] |
| fn cmp(&self, other: &Self) -> Ordering { |
| (*self as usize).cmp(&(*other as usize)) |
| } |
| } |
| |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> hash::Hash for $FnTy { |
| fn hash<HH: hash::Hasher>(&self, state: &mut HH) { |
| state.write_usize(*self as usize) |
| } |
| } |
| |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> fmt::Pointer for $FnTy { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| fmt::Pointer::fmt(&(*self as *const ()), f) |
| } |
| } |
| |
| #[stable(feature = "fnptr_impls", since = "1.4.0")] |
| impl<Ret, $($Arg),*> fmt::Debug for $FnTy { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| fmt::Pointer::fmt(&(*self as *const ()), f) |
| } |
| } |
| } |
| } |
| |
| macro_rules! fnptr_impls_args { |
| ($($Arg: ident),+) => { |
| fnptr_impls_safety_abi! { extern "Rust" fn($($Arg),*) -> Ret, $($Arg),* } |
| fnptr_impls_safety_abi! { extern "C" fn($($Arg),*) -> Ret, $($Arg),* } |
| fnptr_impls_safety_abi! { extern "C" fn($($Arg),* , ...) -> Ret, $($Arg),* } |
| fnptr_impls_safety_abi! { unsafe extern "Rust" fn($($Arg),*) -> Ret, $($Arg),* } |
| fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),*) -> Ret, $($Arg),* } |
| fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),* , ...) -> Ret, $($Arg),* } |
| }; |
| () => { |
| // No variadic functions with 0 parameters |
| fnptr_impls_safety_abi! { extern "Rust" fn() -> Ret, } |
| fnptr_impls_safety_abi! { extern "C" fn() -> Ret, } |
| fnptr_impls_safety_abi! { unsafe extern "Rust" fn() -> Ret, } |
| fnptr_impls_safety_abi! { unsafe extern "C" fn() -> Ret, } |
| }; |
| } |
| |
| fnptr_impls_args! { } |
| fnptr_impls_args! { A } |
| fnptr_impls_args! { A, B } |
| fnptr_impls_args! { A, B, C } |
| fnptr_impls_args! { A, B, C, D } |
| fnptr_impls_args! { A, B, C, D, E } |
| fnptr_impls_args! { A, B, C, D, E, F } |
| fnptr_impls_args! { A, B, C, D, E, F, G } |
| fnptr_impls_args! { A, B, C, D, E, F, G, H } |
| fnptr_impls_args! { A, B, C, D, E, F, G, H, I } |
| fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J } |
| fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K } |
| fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L } |
| |
| // 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 } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: ?Sized> Ord for *mut T { |
| #[inline] |
| fn cmp(&self, other: &*mut 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 *mut T { |
| #[inline] |
| fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> { |
| Some(self.cmp(other)) |
| } |
| |
| #[inline] |
| fn lt(&self, other: &*mut T) -> bool { *self < *other } |
| |
| #[inline] |
| fn le(&self, other: &*mut T) -> bool { *self <= *other } |
| |
| #[inline] |
| fn gt(&self, other: &*mut T) -> bool { *self > *other } |
| |
| #[inline] |
| fn ge(&self, other: &*mut T) -> bool { *self >= *other } |
| } |
| |
| /// A wrapper around a raw non-null `*mut T` that indicates that the possessor |
| /// of this wrapper owns the referent. Useful for building abstractions like |
| /// `Box<T>`, `Vec<T>`, `String`, and `HashMap<K, V>`. |
| /// |
| /// Unlike `*mut T`, `Unique<T>` behaves "as if" it were an instance of `T`. |
| /// It implements `Send`/`Sync` if `T` is `Send`/`Sync`. It also implies |
| /// the kind of strong aliasing guarantees an instance of `T` can expect: |
| /// the referent of the pointer should not be modified without a unique path to |
| /// its owning Unique. |
| /// |
| /// If you're uncertain of whether it's correct to use `Unique` for your purposes, |
| /// consider using `NonNull`, which has weaker semantics. |
| /// |
| /// Unlike `*mut T`, the pointer must always be non-null, even if the pointer |
| /// is never dereferenced. This is so that enums may use this forbidden value |
| /// as a discriminant -- `Option<Unique<T>>` has the same size as `Unique<T>`. |
| /// However the pointer may still dangle if it isn't dereferenced. |
| /// |
| /// Unlike `*mut T`, `Unique<T>` is covariant over `T`. This should always be correct |
| /// for any type which upholds Unique's aliasing requirements. |
| #[unstable(feature = "ptr_internals", issue = "0", |
| reason = "use NonNull instead and consider PhantomData<T> \ |
| (if you also use #[may_dangle]), Send, and/or Sync")] |
| #[doc(hidden)] |
| #[repr(transparent)] |
| pub struct Unique<T: ?Sized> { |
| pointer: NonZero<*const T>, |
| // NOTE: this marker has no consequences for variance, but is necessary |
| // for dropck to understand that we logically own a `T`. |
| // |
| // For details, see: |
| // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data |
| _marker: PhantomData<T>, |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized> fmt::Debug for Unique<T> { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| fmt::Pointer::fmt(&self.as_ptr(), f) |
| } |
| } |
| |
| /// `Unique` pointers are `Send` if `T` is `Send` because the data they |
| /// reference is unaliased. Note that this aliasing invariant is |
| /// unenforced by the type system; the abstraction using the |
| /// `Unique` must enforce it. |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| unsafe impl<T: Send + ?Sized> Send for Unique<T> { } |
| |
| /// `Unique` pointers are `Sync` if `T` is `Sync` because the data they |
| /// reference is unaliased. Note that this aliasing invariant is |
| /// unenforced by the type system; the abstraction using the |
| /// `Unique` must enforce it. |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| unsafe impl<T: Sync + ?Sized> Sync for Unique<T> { } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: Sized> Unique<T> { |
| /// Creates a new `Unique` that is dangling, but well-aligned. |
| /// |
| /// This is useful for initializing types which lazily allocate, like |
| /// `Vec::new` does. |
| /// |
| /// Note that the pointer value may potentially represent a valid pointer to |
| /// a `T`, which means this must not be used as a "not yet initialized" |
| /// sentinel value. Types that lazily allocate must track initialization by |
| /// some other means. |
| // FIXME: rename to dangling() to match NonNull? |
| pub const fn empty() -> Self { |
| unsafe { |
| Unique::new_unchecked(mem::align_of::<T>() as *mut T) |
| } |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized> Unique<T> { |
| /// Creates a new `Unique`. |
| /// |
| /// # Safety |
| /// |
| /// `ptr` must be non-null. |
| pub const unsafe fn new_unchecked(ptr: *mut T) -> Self { |
| Unique { pointer: NonZero(ptr as _), _marker: PhantomData } |
| } |
| |
| /// Creates a new `Unique` if `ptr` is non-null. |
| pub fn new(ptr: *mut T) -> Option<Self> { |
| if !ptr.is_null() { |
| Some(Unique { pointer: NonZero(ptr as _), _marker: PhantomData }) |
| } else { |
| None |
| } |
| } |
| |
| /// Acquires the underlying `*mut` pointer. |
| pub fn as_ptr(self) -> *mut T { |
| self.pointer.0 as *mut T |
| } |
| |
| /// Dereferences the content. |
| /// |
| /// The resulting lifetime is bound to self so this behaves "as if" |
| /// it were actually an instance of T that is getting borrowed. If a longer |
| /// (unbound) lifetime is needed, use `&*my_ptr.as_ptr()`. |
| pub unsafe fn as_ref(&self) -> &T { |
| &*self.as_ptr() |
| } |
| |
| /// Mutably dereferences the content. |
| /// |
| /// The resulting lifetime is bound to self so this behaves "as if" |
| /// it were actually an instance of T that is getting borrowed. If a longer |
| /// (unbound) lifetime is needed, use `&mut *my_ptr.as_ptr()`. |
| pub unsafe fn as_mut(&mut self) -> &mut T { |
| &mut *self.as_ptr() |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized> Clone for Unique<T> { |
| fn clone(&self) -> Self { |
| *self |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized> Copy for Unique<T> { } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized, U: ?Sized> CoerceUnsized<Unique<U>> for Unique<T> where T: Unsize<U> { } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Unique<U>> for Unique<T> where T: Unsize<U> { } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized> fmt::Pointer for Unique<T> { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| fmt::Pointer::fmt(&self.as_ptr(), f) |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<'a, T: ?Sized> From<&'a mut T> for Unique<T> { |
| fn from(reference: &'a mut T) -> Self { |
| Unique { pointer: NonZero(reference as _), _marker: PhantomData } |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<'a, T: ?Sized> From<&'a T> for Unique<T> { |
| fn from(reference: &'a T) -> Self { |
| Unique { pointer: NonZero(reference as _), _marker: PhantomData } |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<'a, T: ?Sized> From<NonNull<T>> for Unique<T> { |
| fn from(p: NonNull<T>) -> Self { |
| Unique { pointer: p.pointer, _marker: PhantomData } |
| } |
| } |
| |
| /// `*mut T` but non-zero and covariant. |
| /// |
| /// This is often the correct thing to use when building data structures using |
| /// raw pointers, but is ultimately more dangerous to use because of its additional |
| /// properties. If you're not sure if you should use `NonNull<T>`, just use `*mut T`! |
| /// |
| /// Unlike `*mut T`, the pointer must always be non-null, even if the pointer |
| /// is never dereferenced. This is so that enums may use this forbidden value |
| /// as a discriminant -- `Option<NonNull<T>>` has the same size as `*mut T`. |
| /// However the pointer may still dangle if it isn't dereferenced. |
| /// |
| /// Unlike `*mut T`, `NonNull<T>` is covariant over `T`. If this is incorrect |
| /// for your use case, you should include some PhantomData in your type to |
| /// provide invariance, such as `PhantomData<Cell<T>>` or `PhantomData<&'a mut T>`. |
| /// Usually this won't be necessary; covariance is correct for most safe abstractions, |
| /// such as Box, Rc, Arc, Vec, and LinkedList. This is the case because they |
| /// provide a public API that follows the normal shared XOR mutable rules of Rust. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[repr(transparent)] |
| pub struct NonNull<T: ?Sized> { |
| pointer: NonZero<*const T>, |
| } |
| |
| /// `NonNull` pointers are not `Send` because the data they reference may be aliased. |
| // NB: This impl is unnecessary, but should provide better error messages. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> !Send for NonNull<T> { } |
| |
| /// `NonNull` pointers are not `Sync` because the data they reference may be aliased. |
| // NB: This impl is unnecessary, but should provide better error messages. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> !Sync for NonNull<T> { } |
| |
| impl<T: Sized> NonNull<T> { |
| /// Creates a new `NonNull` that is dangling, but well-aligned. |
| /// |
| /// This is useful for initializing types which lazily allocate, like |
| /// `Vec::new` does. |
| /// |
| /// Note that the pointer value may potentially represent a valid pointer to |
| /// a `T`, which means this must not be used as a "not yet initialized" |
| /// sentinel value. Types that lazily allocate must track initialization by |
| /// some other means. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[inline] |
| pub fn dangling() -> Self { |
| unsafe { |
| let ptr = mem::align_of::<T>() as *mut T; |
| NonNull::new_unchecked(ptr) |
| } |
| } |
| } |
| |
| impl<T: ?Sized> NonNull<T> { |
| /// Creates a new `NonNull`. |
| /// |
| /// # Safety |
| /// |
| /// `ptr` must be non-null. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[inline] |
| pub const unsafe fn new_unchecked(ptr: *mut T) -> Self { |
| NonNull { pointer: NonZero(ptr as _) } |
| } |
| |
| /// Creates a new `NonNull` if `ptr` is non-null. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[inline] |
| pub fn new(ptr: *mut T) -> Option<Self> { |
| if !ptr.is_null() { |
| Some(NonNull { pointer: NonZero(ptr as _) }) |
| } else { |
| None |
| } |
| } |
| |
| /// Acquires the underlying `*mut` pointer. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[inline] |
| pub const fn as_ptr(self) -> *mut T { |
| self.pointer.0 as *mut T |
| } |
| |
| /// Dereferences the content. |
| /// |
| /// The resulting lifetime is bound to self so this behaves "as if" |
| /// it were actually an instance of T that is getting borrowed. If a longer |
| /// (unbound) lifetime is needed, use `&*my_ptr.as_ptr()`. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[inline] |
| pub unsafe fn as_ref(&self) -> &T { |
| &*self.as_ptr() |
| } |
| |
| /// Mutably dereferences the content. |
| /// |
| /// The resulting lifetime is bound to self so this behaves "as if" |
| /// it were actually an instance of T that is getting borrowed. If a longer |
| /// (unbound) lifetime is needed, use `&mut *my_ptr.as_ptr()`. |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| #[inline] |
| pub unsafe fn as_mut(&mut self) -> &mut T { |
| &mut *self.as_ptr() |
| } |
| |
| /// Cast to a pointer of another type |
| #[stable(feature = "nonnull_cast", since = "1.27.0")] |
| #[inline] |
| pub fn cast<U>(self) -> NonNull<U> { |
| unsafe { |
| NonNull::new_unchecked(self.as_ptr() as *mut U) |
| } |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> Clone for NonNull<T> { |
| fn clone(&self) -> Self { |
| *self |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> Copy for NonNull<T> { } |
| |
| #[unstable(feature = "coerce_unsized", issue = "27732")] |
| impl<T: ?Sized, U: ?Sized> CoerceUnsized<NonNull<U>> for NonNull<T> where T: Unsize<U> { } |
| |
| #[unstable(feature = "dispatch_from_dyn", issue = "0")] |
| impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: Unsize<U> { } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> fmt::Debug for NonNull<T> { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| fmt::Pointer::fmt(&self.as_ptr(), f) |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> fmt::Pointer for NonNull<T> { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| fmt::Pointer::fmt(&self.as_ptr(), f) |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> Eq for NonNull<T> {} |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> PartialEq for NonNull<T> { |
| #[inline] |
| fn eq(&self, other: &Self) -> bool { |
| self.as_ptr() == other.as_ptr() |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> Ord for NonNull<T> { |
| #[inline] |
| fn cmp(&self, other: &Self) -> Ordering { |
| self.as_ptr().cmp(&other.as_ptr()) |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> PartialOrd for NonNull<T> { |
| #[inline] |
| fn partial_cmp(&self, other: &Self) -> Option<Ordering> { |
| self.as_ptr().partial_cmp(&other.as_ptr()) |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<T: ?Sized> hash::Hash for NonNull<T> { |
| #[inline] |
| fn hash<H: hash::Hasher>(&self, state: &mut H) { |
| self.as_ptr().hash(state) |
| } |
| } |
| |
| #[unstable(feature = "ptr_internals", issue = "0")] |
| impl<T: ?Sized> From<Unique<T>> for NonNull<T> { |
| #[inline] |
| fn from(unique: Unique<T>) -> Self { |
| NonNull { pointer: unique.pointer } |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T> { |
| #[inline] |
| fn from(reference: &'a mut T) -> Self { |
| NonNull { pointer: NonZero(reference as _) } |
| } |
| } |
| |
| #[stable(feature = "nonnull", since = "1.25.0")] |
| impl<'a, T: ?Sized> From<&'a T> for NonNull<T> { |
| #[inline] |
| fn from(reference: &'a T) -> Self { |
| NonNull { pointer: NonZero(reference as _) } |
| } |
| } |