squiid/rust
1
0
Fork 0
Code Issues Pull requests Projects Activity

address more review comments

Browse source 
* `cfg` only the body of `align_offset`
* put explicit panics back
* explain why `ptr.align_offset(align) == 0` is slow
This commit is contained in:
Lukas Markeffsky 2022-10-22 21:20:04 +02:00
parent 093c02ed46
commit df0bcfe644
2 changed files with 54 additions and 58 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

56
library/core/src/ptr/const_ptr.rs
View file

@ -1323,21 +1323,6 @@ impl<T: ?Sized> *const T {
#[must_use]
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
#[cfg(not(bootstrap))]
pub const fn align_offset(self, align: usize) -> usize
where
T: Sized,
{
assert!(align.is_power_of_two(), "align_offset: align is not a power-of-two");
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(self, align) }
}
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
#[allow(missing_docs)]
#[cfg(bootstrap)]
pub const fn align_offset(self, align: usize) -> usize
where
T: Sized,
@ -1346,21 +1331,30 @@ impl<T: ?Sized> *const T {
panic!("align_offset: align is not a power-of-two");
}
fn rt_impl<T>(p: *const T, align: usize) -> usize {
#[cfg(bootstrap)]
{
fn rt_impl<T>(p: *const T, align: usize) -> usize {
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(p, align) }
}
const fn ctfe_impl<T>(_: *const T, _: usize) -> usize {
usize::MAX
}
// SAFETY:
// It is permissible for `align_offset` to always return `usize::MAX`,
// algorithm correctness can not depend on `align_offset` returning non-max values.
//
// As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
}
#[cfg(not(bootstrap))]
{
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(p, align) }
unsafe { align_offset(self, align) }
}
const fn ctfe_impl<T>(_: *const T, _: usize) -> usize {
usize::MAX
}
// SAFETY:
// It is permissible for `align_offset` to always return `usize::MAX`,
// algorithm correctness can not depend on `align_offset` returning non-max values.
//
// As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
}
/// Returns whether the pointer is properly aligned for `T`.
@ -1522,13 +1516,17 @@ impl<T: ?Sized> *const T {
#[unstable(feature = "pointer_is_aligned", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "none")]
pub const fn is_aligned_to(self, align: usize) -> bool {
assert!(align.is_power_of_two(), "is_aligned_to: align is not a power-of-two");
if !align.is_power_of_two() {
panic!("is_aligned_to: align is not a power-of-two")
}
#[inline]
fn runtime(ptr: *const u8, align: usize) -> bool {
ptr.addr() & (align - 1) == 0
}
// This optimizes to `(ptr + align - 1) & -align == ptr`, which is slightly
// slower than `ptr & (align - 1) == 0`
const fn comptime(ptr: *const u8, align: usize) -> bool {
ptr.align_offset(align) == 0
}

56
library/core/src/ptr/mut_ptr.rs
View file

@ -1591,21 +1591,6 @@ impl<T: ?Sized> *mut T {
#[must_use]
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
#[cfg(not(bootstrap))]
pub const fn align_offset(self, align: usize) -> usize
where
T: Sized,
{
assert!(align.is_power_of_two(), "align_offset: align is not a power-of-two");
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(self, align) }
}
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
#[allow(missing_docs)]
#[cfg(bootstrap)]
pub const fn align_offset(self, align: usize) -> usize
where
T: Sized,
@ -1614,21 +1599,30 @@ impl<T: ?Sized> *mut T {
panic!("align_offset: align is not a power-of-two");
}
fn rt_impl<T>(p: *mut T, align: usize) -> usize {
#[cfg(bootstrap)]
{
fn rt_impl<T>(p: *mut T, align: usize) -> usize {
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(p, align) }
}
const fn ctfe_impl<T>(_: *mut T, _: usize) -> usize {
usize::MAX
}
// SAFETY:
// It is permissible for `align_offset` to always return `usize::MAX`,
// algorithm correctness can not depend on `align_offset` returning non-max values.
//
// As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
}
#[cfg(not(bootstrap))]
{
// SAFETY: `align` has been checked to be a power of 2 above
unsafe { align_offset(p, align) }
unsafe { align_offset(self, align) }
}
const fn ctfe_impl<T>(_: *mut T, _: usize) -> usize {
usize::MAX
}
// SAFETY:
// It is permissible for `align_offset` to always return `usize::MAX`,
// algorithm correctness can not depend on `align_offset` returning non-max values.
//
// As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
}
/// Returns whether the pointer is properly aligned for `T`.
@ -1790,13 +1784,17 @@ impl<T: ?Sized> *mut T {
#[unstable(feature = "pointer_is_aligned", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "none")]
pub const fn is_aligned_to(self, align: usize) -> bool {
assert!(align.is_power_of_two(), "is_aligned_to: align is not a power-of-two");
if !align.is_power_of_two() {
panic!("is_aligned_to: align is not a power-of-two")
}
#[inline]
fn runtime(ptr: *mut u8, align: usize) -> bool {
ptr.addr() & (align - 1) == 0
}
// This optimizes to `(ptr + align - 1) & -align == ptr`, which is slightly
// slower than `ptr & (align - 1) == 0`
const fn comptime(ptr: *mut u8, align: usize) -> bool {
ptr.align_offset(align) == 0
}