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Sep 30, 2019
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Simplify ArrayView construction from NonNull<T> and add RawView .cast() method #734

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5447af8
FIX: Use NonNull internal constructors for Raw/ArrayView/Mut
bluss Sep 29, 2019
ac55d74
FEAT: Add methods RawArrayView/Mut::cast
bluss Sep 29, 2019
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10 changes: 5 additions & 5 deletions src/impl_methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -139,7 +139,7 @@ where
S: Data,
{
debug_assert!(self.pointer_is_inbounds());
unsafe { ArrayView::new_(self.ptr.as_ptr(), self.dim.clone(), self.strides.clone()) }
unsafe { ArrayView::new(self.ptr, self.dim.clone(), self.strides.clone()) }
}

/// Return a read-write view of the array
Expand All @@ -148,7 +148,7 @@ where
S: DataMut,
{
self.ensure_unique();
unsafe { ArrayViewMut::new_(self.ptr.as_ptr(), self.dim.clone(), self.strides.clone()) }
unsafe { ArrayViewMut::new(self.ptr, self.dim.clone(), self.strides.clone()) }
}

/// Return an uniquely owned copy of the array.
Expand Down Expand Up @@ -1313,7 +1313,7 @@ where
/// Return a raw view of the array.
#[inline]
pub fn raw_view(&self) -> RawArrayView<A, D> {
unsafe { RawArrayView::new_(self.ptr.as_ptr(), self.dim.clone(), self.strides.clone()) }
unsafe { RawArrayView::new(self.ptr, self.dim.clone(), self.strides.clone()) }
}

/// Return a raw mutable view of the array.
Expand All @@ -1323,7 +1323,7 @@ where
S: RawDataMut,
{
self.try_ensure_unique(); // for RcArray
unsafe { RawArrayViewMut::new_(self.ptr.as_ptr(), self.dim.clone(), self.strides.clone()) }
unsafe { RawArrayViewMut::new(self.ptr, self.dim.clone(), self.strides.clone()) }
}

/// Return the array’s data as a slice, if it is contiguous and in standard order.
Expand Down Expand Up @@ -1620,7 +1620,7 @@ where
Some(st) => st,
None => return None,
};
unsafe { Some(ArrayView::new_(self.ptr.as_ptr(), dim, broadcast_strides)) }
unsafe { Some(ArrayView::new(self.ptr, dim, broadcast_strides)) }
}

/// Swap axes `ax` and `bx`.
Expand Down
87 changes: 75 additions & 12 deletions src/impl_raw_views.rs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,6 @@
use std::mem;
use std::ptr::NonNull;

use crate::dimension::{self, stride_offset};
use crate::extension::nonnull::nonnull_debug_checked_from_ptr;
use crate::imp_prelude::*;
Expand All @@ -11,16 +14,20 @@ where
///
/// Unsafe because caller is responsible for ensuring that the array will
/// meet all of the invariants of the `ArrayBase` type.
#[inline(always)]
pub(crate) unsafe fn new_(ptr: *const A, dim: D, strides: D) -> Self {
#[inline]
pub(crate) unsafe fn new(ptr: NonNull<A>, dim: D, strides: D) -> Self {
RawArrayView {
data: RawViewRepr::new(),
ptr: nonnull_debug_checked_from_ptr(ptr as *mut _),
ptr,
dim,
strides,
}
}

unsafe fn new_(ptr: *const A, dim: D, strides: D) -> Self {
Self::new(nonnull_debug_checked_from_ptr(ptr as *mut A), dim, strides)
}

/// Create an `RawArrayView<A, D>` from shape information and a raw pointer
/// to the elements.
///
Expand Down Expand Up @@ -76,7 +83,7 @@ where
/// ensure that all of the data is valid and choose the correct lifetime.
#[inline]
pub unsafe fn deref_into_view<'a>(self) -> ArrayView<'a, A, D> {
ArrayView::new_(self.ptr.as_ptr(), self.dim, self.strides)
ArrayView::new(self.ptr, self.dim, self.strides)
}

/// Split the array view along `axis` and return one array pointer strictly
Expand Down Expand Up @@ -105,6 +112,32 @@ where

(left, right)
}

/// Cast the raw pointer of the raw array view to a different type
///
/// **Panics** if element size is not compatible.
///
/// Lack of panic does not imply it is a valid cast. The cast works the same
/// way as regular raw pointer casts.
///
/// While this method is safe, for the same reason as regular raw pointer
/// casts are safe, access through the produced raw view is only possible
/// in an unsafe block or function.
pub fn cast<B>(self) -> RawArrayView<B, D> {
assert_eq!(
mem::size_of::<B>(),
mem::size_of::<A>(),
"size mismatch in raw view cast"
);
let ptr = self.ptr.cast::<B>();
debug_assert!(
is_aligned(ptr.as_ptr()),
"alignment mismatch in raw view cast"
);
/* Alignment checked with debug assertion: alignment could be dynamically correct,
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Since this is a safe function, we need to either assert! (not debug_assert!) that the pointer is aligned (which would be my preference), or we need to relax the "ptr must always be aligned" requirement on ArrayBase.

To avoid the cost of the check in most cases, we could write it like this:

if mem::align_of<A>() % mem::align_of<B>() != 0 {
    assert!(is_aligned(ptr.as_ptr()), "incompatible alignment in raw view cast");
}

or, equivalently, since "alignment is measured in bytes, and must be at least 1, and always a power of 2":

if mem::align_of<B>() > mem::align_of<A>() {
    assert!(is_aligned(ptr.as_ptr()), "incompatible alignment in raw view cast");
}

The comparison in the if should always compile out, and the body of the if will remain only if the alignment of B is greater than the alignment of A. I would expect that case to be relatively rare, because it requires additional work on the part of the user (since the pointer to A won't naturally be guaranteed to have valid alignment for B).

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@bluss bluss Oct 2, 2019 •
edited
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Where does the alignment requirement come from, and doesn't it only matter if we dereference?

I'd prefer to make this function unsafe, there is basically no downside to that, instead of adding checking that does not compile out.

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I'm referring to this constraint on ArrayBase. From what I can tell, you're right -- the only time alignment actually matters for RawArrayView/Mut is when dereferencing a pointer or reading/writing a pointed-to value in some way (i.e. most of the functions in std::ptr).

It sounds like the best option is to remove the alignment restriction on RawArrayView/Mut. All we'd need to do is update the list of restrictions in that comment above ArrayBase, the docs for RawArrayView/Mut::from_shape_ptr, and the docs for deref_into_view/_mut.

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I've created #738 to remove the alignment restriction on RawArrayView/Mut.

* and we don't have a check that compiles out for that. */
unsafe { RawArrayView::new(ptr, self.dim, self.strides) }
}
}

impl<A, D> RawArrayViewMut<A, D>
Expand All @@ -115,16 +148,20 @@ where
///
/// Unsafe because caller is responsible for ensuring that the array will
/// meet all of the invariants of the `ArrayBase` type.
#[inline(always)]
pub(crate) unsafe fn new_(ptr: *mut A, dim: D, strides: D) -> Self {
#[inline]
pub(crate) unsafe fn new(ptr: NonNull<A>, dim: D, strides: D) -> Self {
RawArrayViewMut {
data: RawViewRepr::new(),
ptr: nonnull_debug_checked_from_ptr(ptr),
ptr,
dim,
strides,
}
}

unsafe fn new_(ptr: *mut A, dim: D, strides: D) -> Self {
Self::new(nonnull_debug_checked_from_ptr(ptr), dim, strides)
}

/// Create an `RawArrayViewMut<A, D>` from shape information and a raw
/// pointer to the elements.
///
Expand Down Expand Up @@ -176,7 +213,7 @@ where
/// Converts to a non-mutable `RawArrayView`.
#[inline]
pub(crate) fn into_raw_view(self) -> RawArrayView<A, D> {
unsafe { RawArrayView::new_(self.ptr.as_ptr(), self.dim, self.strides) }
unsafe { RawArrayView::new(self.ptr, self.dim, self.strides) }
}

/// Converts to a read-only view of the array.
Expand All @@ -186,7 +223,7 @@ where
/// ensure that all of the data is valid and choose the correct lifetime.
#[inline]
pub unsafe fn deref_into_view<'a>(self) -> ArrayView<'a, A, D> {
ArrayView::new_(self.ptr.as_ptr(), self.dim, self.strides)
ArrayView::new(self.ptr, self.dim, self.strides)
}

/// Converts to a mutable view of the array.
Expand All @@ -196,7 +233,7 @@ where
/// ensure that all of the data is valid and choose the correct lifetime.
#[inline]
pub unsafe fn deref_into_view_mut<'a>(self) -> ArrayViewMut<'a, A, D> {
ArrayViewMut::new_(self.ptr.as_ptr(), self.dim, self.strides)
ArrayViewMut::new(self.ptr, self.dim, self.strides)
}

/// Split the array view along `axis` and return one array pointer strictly
Expand All @@ -207,9 +244,35 @@ where
let (left, right) = self.into_raw_view().split_at(axis, index);
unsafe {
(
Self::new_(left.ptr.as_ptr(), left.dim, left.strides),
Self::new_(right.ptr.as_ptr(), right.dim, right.strides),
Self::new(left.ptr, left.dim, left.strides),
Self::new(right.ptr, right.dim, right.strides),
)
}
}

/// Cast the raw pointer of the raw array view to a different type
///
/// **Panics** if element size is not compatible.
///
/// Lack of panic does not imply it is a valid cast. The cast works the same
/// way as regular raw pointer casts.
///
/// While this method is safe, for the same reason as regular raw pointer
/// casts are safe, access through the produced raw view is only possible
/// in an unsafe block or function.
pub fn cast<B>(self) -> RawArrayViewMut<B, D> {
assert_eq!(
mem::size_of::<B>(),
mem::size_of::<A>(),
"size mismatch in raw view cast"
);
let ptr = self.ptr.cast::<B>();
debug_assert!(
is_aligned(ptr.as_ptr()),
"alignment mismatch in raw view cast"
);
/* Alignment checked with debug assertion: alignment could be dynamically correct,
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Same thing here -- the alignment check is a safety issue, so it should be assert!, not debug_assert!.

* and we don't have a check that compiles out for that. */
unsafe { RawArrayViewMut::new(ptr, self.dim, self.strides) }
}
}
35 changes: 27 additions & 8 deletions src/impl_views/constructors.rs
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Expand Up @@ -6,6 +6,8 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::ptr::NonNull;

use crate::dimension;
use crate::error::ShapeError;
use crate::extension::nonnull::nonnull_debug_checked_from_ptr;
Expand Down Expand Up @@ -200,11 +202,11 @@ where

/// Convert the view into an `ArrayViewMut<'b, A, D>` where `'b` is a lifetime
/// outlived by `'a'`.
pub fn reborrow<'b>(mut self) -> ArrayViewMut<'b, A, D>
pub fn reborrow<'b>(self) -> ArrayViewMut<'b, A, D>
where
'a: 'b,
{
unsafe { ArrayViewMut::new_(self.as_mut_ptr(), self.dim, self.strides) }
unsafe { ArrayViewMut::new(self.ptr, self.dim, self.strides) }
}
}

Expand All @@ -217,14 +219,24 @@ where
///
/// Unsafe because: `ptr` must be valid for the given dimension and strides.
#[inline(always)]
pub(crate) unsafe fn new_(ptr: *const A, dim: D, strides: D) -> Self {
pub(crate) unsafe fn new(ptr: NonNull<A>, dim: D, strides: D) -> Self {
if cfg!(debug_assertions) {
assert!(is_aligned(ptr.as_ptr()), "The pointer must be aligned.");
dimension::max_abs_offset_check_overflow::<A, _>(&dim, &strides).unwrap();
}
ArrayView {
data: ViewRepr::new(),
ptr: nonnull_debug_checked_from_ptr(ptr as *mut A),
ptr,
dim,
strides,
}
}

/// Unsafe because: `ptr` must be valid for the given dimension and strides.
#[inline]
pub(crate) unsafe fn new_(ptr: *const A, dim: D, strides: D) -> Self {
Self::new(nonnull_debug_checked_from_ptr(ptr as *mut A), dim, strides)
}
}

impl<'a, A, D> ArrayViewMut<'a, A, D>
Expand All @@ -235,17 +247,24 @@ where
///
/// Unsafe because: `ptr` must be valid for the given dimension and strides.
#[inline(always)]
pub(crate) unsafe fn new_(ptr: *mut A, dim: D, strides: D) -> Self {
pub(crate) unsafe fn new(ptr: NonNull<A>, dim: D, strides: D) -> Self {
if cfg!(debug_assertions) {
assert!(!ptr.is_null(), "The pointer must be non-null.");
assert!(is_aligned(ptr), "The pointer must be aligned.");
assert!(is_aligned(ptr.as_ptr()), "The pointer must be aligned.");
dimension::max_abs_offset_check_overflow::<A, _>(&dim, &strides).unwrap();
}
ArrayViewMut {
data: ViewRepr::new(),
ptr: nonnull_debug_checked_from_ptr(ptr),
ptr,
dim,
strides,
}
}

/// Create a new `ArrayView`
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Typo: This should be ArrayViewMut (same for the docs of new above).

///
/// Unsafe because: `ptr` must be valid for the given dimension and strides.
#[inline(always)]
pub(crate) unsafe fn new_(ptr: *mut A, dim: D, strides: D) -> Self {
Self::new(nonnull_debug_checked_from_ptr(ptr), dim, strides)
}
}
8 changes: 4 additions & 4 deletions src/impl_views/conversions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ where
where
'a: 'b,
{
unsafe { ArrayView::new_(self.as_ptr(), self.dim, self.strides) }
unsafe { ArrayView::new(self.ptr, self.dim, self.strides) }
}

/// Return the array’s data as a slice, if it is contiguous and in standard order.
Expand All @@ -53,7 +53,7 @@ where

/// Converts to a raw array view.
pub(crate) fn into_raw_view(self) -> RawArrayView<A, D> {
unsafe { RawArrayView::new_(self.ptr.as_ptr(), self.dim, self.strides) }
unsafe { RawArrayView::new(self.ptr, self.dim, self.strides) }
}
}

Expand Down Expand Up @@ -161,12 +161,12 @@ where
{
// Convert into a read-only view
pub(crate) fn into_view(self) -> ArrayView<'a, A, D> {
unsafe { ArrayView::new_(self.ptr.as_ptr(), self.dim, self.strides) }
unsafe { ArrayView::new(self.ptr, self.dim, self.strides) }
}

/// Converts to a mutable raw array view.
pub(crate) fn into_raw_view_mut(self) -> RawArrayViewMut<A, D> {
unsafe { RawArrayViewMut::new_(self.ptr.as_ptr(), self.dim, self.strides) }
unsafe { RawArrayViewMut::new(self.ptr, self.dim, self.strides) }
}

#[inline]
Expand Down
2 changes: 1 addition & 1 deletion src/lib.rs
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Expand Up @@ -1517,7 +1517,7 @@ where
let ptr = self.ptr;
let mut strides = dim.clone();
strides.slice_mut().copy_from_slice(self.strides.slice());
unsafe { ArrayView::new_(ptr.as_ptr(), dim, strides) }
unsafe { ArrayView::new(ptr, dim, strides) }
}

fn raw_strides(&self) -> D {
Expand Down
2 changes: 1 addition & 1 deletion src/zip/mod.rs
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Expand Up @@ -73,7 +73,7 @@ where
type Output = ArrayView<'a, A, E::Dim>;
fn broadcast_unwrap(self, shape: E) -> Self::Output {
let res: ArrayView<'_, A, E::Dim> = (&self).broadcast_unwrap(shape.into_dimension());
unsafe { ArrayView::new_(res.ptr.as_ptr(), res.dim, res.strides) }
unsafe { ArrayView::new(res.ptr, res.dim, res.strides) }
}
private_impl! {}
}
Expand Down
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