ring/arithmetic/inout.rs
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// Copyright 2025 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
pub(crate) use crate::error::LenMismatchError;
use core::num::NonZeroUsize;
pub(crate) trait AliasingSlices2<T> {
/// The pointers passed to `f` will be valid and non-null, and will not
/// be dangling, so they can be passed to C functions.
///
/// The first pointer, `r`, may be pointing to uninitialized memory for
/// `expected_len` elements of type `T`, properly aligned and writable.
/// `f` must not read from `r` before writing to it.
///
/// The second & third pointers, `a` and `b`, point to `expected_len`
/// values of type `T`, properly aligned.
///
/// `r`, `a`, and/or `b` may alias each other only in the following ways:
/// `ptr::eq(r, a)`, `ptr::eq(r, b)`, and/or `ptr::eq(a, b)`; i.e. they
/// will not be "overlapping."
///
/// Implementations of this trait shouldn't override this default
/// implementation.
#[inline(always)]
fn with_non_dangling_non_null_pointers_ra<R>(
self,
expected_len: NonZeroUsize,
f: impl FnOnce(*mut T, *const T) -> R,
) -> Result<R, LenMismatchError>
where
Self: Sized,
{
self.with_potentially_dangling_non_null_pointers_ra(expected_len.get(), f)
}
/// If `expected_len == 0` then the pointers passed to `f` may be
/// dangling pointers, which should not be passed to C functions. In all
/// other respects, this works like
/// `Self::with_non_dangling_non_null_pointers_rab`.
///
/// Implementations of this trait should implement this method and not
/// `with_non_dangling_non_null_pointers_rab`. Users of this trait should
/// use `with_non_dangling_non_null_pointers_rab` and not this.
fn with_potentially_dangling_non_null_pointers_ra<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T) -> R,
) -> Result<R, LenMismatchError>;
}
impl<T> AliasingSlices2<T> for &mut [T] {
fn with_potentially_dangling_non_null_pointers_ra<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T) -> R,
) -> Result<R, LenMismatchError> {
let r = self;
if r.len() != expected_len {
return Err(LenMismatchError::new(r.len()));
}
Ok(f(r.as_mut_ptr(), r.as_ptr()))
}
}
impl<T> AliasingSlices2<T> for (&mut [T], &[T]) {
fn with_potentially_dangling_non_null_pointers_ra<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T) -> R,
) -> Result<R, LenMismatchError> {
let (r, a) = self;
if r.len() != expected_len {
return Err(LenMismatchError::new(r.len()));
}
if a.len() != expected_len {
return Err(LenMismatchError::new(a.len()));
}
Ok(f(r.as_mut_ptr(), a.as_ptr()))
}
}
pub(crate) trait AliasingSlices3<T> {
/// The pointers passed to `f` will all be non-null and properly aligned,
/// and will not be dangling.
///
/// The first pointer, `r` points to potentially-uninitialized writable
/// space for `expected_len` elements of type `T`. Accordingly, `f` must
/// not read from `r` before writing to it.
///
/// The second & third pointers, `a` and `b`, point to `expected_len`
/// initialized values of type `T`.
///
/// `r`, `a`, and/or `b` may alias each other, but only in the following
/// ways: `ptr::eq(r, a)`, `ptr::eq(r, b)`, and/or `ptr::eq(a, b)`; they
/// will not be "overlapping."
///
/// Implementations of this trait shouldn't override this default
/// implementation.
#[inline(always)]
fn with_non_dangling_non_null_pointers_rab<R>(
self,
expected_len: NonZeroUsize,
f: impl FnOnce(*mut T, *const T, *const T) -> R,
) -> Result<R, LenMismatchError>
where
Self: Sized,
{
self.with_potentially_dangling_non_null_pointers_rab(expected_len.get(), f)
}
/// If `expected_len == 0` then the pointers passed to `f` may be
/// dangling pointers, which should not be passed to C functions. In all
/// other respects, this works like
/// `Self::with_non_dangling_non_null_pointers_rab`.
///
/// Implementations of this trait should implement this method and not
/// `with_non_dangling_non_null_pointers_rab`. Users of this trait should
/// use `with_non_dangling_non_null_pointers_rab` and not this.
fn with_potentially_dangling_non_null_pointers_rab<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T, *const T) -> R,
) -> Result<R, LenMismatchError>;
}
impl<T> AliasingSlices3<T> for &mut [T] {
fn with_potentially_dangling_non_null_pointers_rab<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T, *const T) -> R,
) -> Result<R, LenMismatchError> {
<Self as AliasingSlices2<T>>::with_potentially_dangling_non_null_pointers_ra(
self,
expected_len,
|r, a| f(r, r, a),
)
}
}
impl<T> AliasingSlices3<T> for (&mut [T], &[T], &[T]) {
fn with_potentially_dangling_non_null_pointers_rab<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T, *const T) -> R,
) -> Result<R, LenMismatchError> {
let (r, a, b) = self;
((r, a), b).with_potentially_dangling_non_null_pointers_rab(expected_len, f)
}
}
impl<RA, T> AliasingSlices3<T> for (RA, &[T])
where
RA: AliasingSlices2<T>,
{
fn with_potentially_dangling_non_null_pointers_rab<R>(
self,
expected_len: usize,
f: impl FnOnce(*mut T, *const T, *const T) -> R,
) -> Result<R, LenMismatchError> {
let (ra, b) = self;
if b.len() != expected_len {
return Err(LenMismatchError::new(b.len()));
}
ra.with_potentially_dangling_non_null_pointers_ra(expected_len, |r, a| f(r, a, b.as_ptr()))
}
}