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core: begin deduplicating pointer docs #141609

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63 changes: 2 additions & 61 deletions library/core/src/ptr/const_ptr.rs
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -397,35 +397,7 @@ impl<T: ?Sized> *const T {
if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
}

/// Adds a signed offset to 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:
///
/// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
/// "wrapping around"), must fit in an `isize`.
///
/// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
/// [allocated object], and the entire memory range between `self` and the result must be in
/// bounds of that allocated object. In particular, this range must not "wrap around" the edge
/// of the address space. Note that "range" here refers to a half-open range as usual in Rust,
/// i.e., `self..result` for non-negative offsets and `result..self` for negative offsets.
///
/// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
/// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
/// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
/// safe.
///
/// Consider using [`wrapping_offset`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_offset`]: #method.wrapping_offset
/// [allocated object]: crate::ptr#allocated-object
#[doc = include_str!("./docs/offset.md")]
///
/// # Examples
///
Expand Down Expand Up @@ -905,38 +877,7 @@ impl<T: ?Sized> *const T {
}
}

/// Adds an unsigned offset to a pointer.
///
/// This can only move the pointer forward (or not move it). If you need to move forward or
/// backward depending on the value, then you might want [`offset`](#method.offset) instead
/// which takes a signed offset.
///
/// `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:
///
/// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
/// "wrapping around"), must fit in an `isize`.
///
/// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
/// [allocated object], and the entire memory range between `self` and the result must be in
/// bounds of that allocated object. In particular, this range must not "wrap around" the edge
/// of the address space.
///
/// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
/// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
/// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
/// safe.
///
/// Consider using [`wrapping_add`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_add`]: #method.wrapping_add
/// [allocated object]: crate::ptr#allocated-object
#[doc = include_str!("./docs/add.md")]
///
/// # Examples
///
Expand Down
32 changes: 32 additions & 0 deletions library/core/src/ptr/docs/add.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,32 @@
Adds an unsigned offset to a pointer.

This can only move the pointer forward (or not move it). If you need to move forward or
backward depending on the value, then you might want [`offset`](#method.offset) instead
which takes a signed offset.

`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:

* The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
"wrapping around"), must fit in an `isize`.

* If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
[allocated object], and the entire memory range between `self` and the result must be in
bounds of that allocated object. In particular, this range must not "wrap around" the edge
of the address space.

Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
safe.

Consider using [`wrapping_add`] instead if these constraints are
difficult to satisfy. The only advantage of this method is that it
enables more aggressive compiler optimizations.

[`wrapping_add`]: #method.wrapping_add
[allocated object]: crate::ptr#allocated-object
29 changes: 29 additions & 0 deletions library/core/src/ptr/docs/offset.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
Adds a signed offset to 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:

* The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
"wrapping around"), must fit in an `isize`.

* If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
[allocated object], and the entire memory range between `self` and the result must be in
bounds of that allocated object. In particular, this range must not "wrap around" the edge
of the address space. Note that "range" here refers to a half-open range as usual in Rust,
i.e., `self..result` for non-negative offsets and `result..self` for negative offsets.

Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
safe.

Consider using [`wrapping_offset`] instead if these constraints are
difficult to satisfy. The only advantage of this method is that it
enables more aggressive compiler optimizations.

[`wrapping_offset`]: #method.wrapping_offset
[allocated object]: crate::ptr#allocated-object
66 changes: 4 additions & 62 deletions library/core/src/ptr/mut_ptr.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -394,34 +394,7 @@ impl<T: ?Sized> *mut T {
if self.is_null() { None } else { Some(unsafe { &*(self as *const MaybeUninit<T>) }) }
}

/// Adds a signed offset to 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:
///
/// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
/// "wrapping around"), must fit in an `isize`.
///
/// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
/// [allocated object], and the entire memory range between `self` and the result must be in
/// bounds of that allocated object. In particular, this range must not "wrap around" the edge
/// of the address space.
///
/// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
/// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
/// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
/// safe.
///
/// Consider using [`wrapping_offset`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_offset`]: #method.wrapping_offset
/// [allocated object]: crate::ptr#allocated-object
#[doc = include_str!("./docs/offset.md")]
///
/// # Examples
///
Expand Down Expand Up @@ -996,44 +969,13 @@ impl<T: ?Sized> *mut T {
unsafe { (self as *const T).byte_offset_from_unsigned(origin) }
}

/// Adds an unsigned offset to a pointer.
///
/// This can only move the pointer forward (or not move it). If you need to move forward or
/// backward depending on the value, then you might want [`offset`](#method.offset) instead
/// which takes a signed offset.
///
/// `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:
///
/// * The offset in bytes, `count * size_of::<T>()`, computed on mathematical integers (without
/// "wrapping around"), must fit in an `isize`.
///
/// * If the computed offset is non-zero, then `self` must be [derived from][crate::ptr#provenance] a pointer to some
/// [allocated object], and the entire memory range between `self` and the result must be in
/// bounds of that allocated object. In particular, this range must not "wrap around" the edge
/// of the address space.
///
/// Allocated objects can never be larger than `isize::MAX` bytes, so if the computed offset
/// stays in bounds of the allocated object, it is guaranteed to satisfy the first requirement.
/// This implies, for instance, that `vec.as_ptr().add(vec.len())` (for `vec: Vec<T>`) is always
/// safe.
///
/// Consider using [`wrapping_add`] instead if these constraints are
/// difficult to satisfy. The only advantage of this method is that it
/// enables more aggressive compiler optimizations.
///
/// [`wrapping_add`]: #method.wrapping_add
/// [allocated object]: crate::ptr#allocated-object
#[doc = include_str!("./docs/add.md")]
///
/// # Examples
///
/// ```
/// let s: &str = "123";
/// let ptr: *const u8 = s.as_ptr();
/// let mut s: String = "123".to_string();
/// let ptr: *mut u8 = s.as_mut_ptr();
///
/// unsafe {
/// assert_eq!('2', *ptr.add(1) as char);
Expand Down
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