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slice: Mark rotate_left
, rotate_right
unstably const
#143554
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -1,5 +1,5 @@ | ||
use crate::mem::{MaybeUninit, SizedTypeProperties}; | ||
use crate::{cmp, ptr}; | ||
use crate::ptr; | ||
|
||
type BufType = [usize; 32]; | ||
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||
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@@ -11,7 +11,7 @@ type BufType = [usize; 32]; | |
/// | ||
/// The specified range must be valid for reading and writing. | ||
#[inline] | ||
pub(super) unsafe fn ptr_rotate<T>(left: usize, mid: *mut T, right: usize) { | ||
pub(super) const unsafe fn ptr_rotate<T>(left: usize, mid: *mut T, right: usize) { | ||
if T::IS_ZST { | ||
return; | ||
} | ||
|
@@ -21,7 +21,8 @@ pub(super) unsafe fn ptr_rotate<T>(left: usize, mid: *mut T, right: usize) { | |
} | ||
// `T` is not a zero-sized type, so it's okay to divide by its size. | ||
if !cfg!(feature = "optimize_for_size") | ||
&& cmp::min(left, right) <= size_of::<BufType>() / size_of::<T>() | ||
// FIXME(const-hack): Use cmp::min when available in const | ||
&& min(left, right) <= size_of::<BufType>() / size_of::<T>() | ||
{ | ||
// SAFETY: guaranteed by the caller | ||
unsafe { ptr_rotate_memmove(left, mid, right) }; | ||
|
@@ -45,7 +46,7 @@ pub(super) unsafe fn ptr_rotate<T>(left: usize, mid: *mut T, right: usize) { | |
/// | ||
/// The specified range must be valid for reading and writing. | ||
#[inline] | ||
unsafe fn ptr_rotate_memmove<T>(left: usize, mid: *mut T, right: usize) { | ||
const unsafe fn ptr_rotate_memmove<T>(left: usize, mid: *mut T, right: usize) { | ||
// The `[T; 0]` here is to ensure this is appropriately aligned for T | ||
let mut rawarray = MaybeUninit::<(BufType, [T; 0])>::uninit(); | ||
let buf = rawarray.as_mut_ptr() as *mut T; | ||
|
@@ -117,7 +118,7 @@ unsafe fn ptr_rotate_memmove<T>(left: usize, mid: *mut T, right: usize) { | |
/// | ||
/// The specified range must be valid for reading and writing. | ||
#[inline] | ||
unsafe fn ptr_rotate_gcd<T>(left: usize, mid: *mut T, right: usize) { | ||
const unsafe fn ptr_rotate_gcd<T>(left: usize, mid: *mut T, right: usize) { | ||
// Algorithm 2 | ||
// Microbenchmarks indicate that the average performance for random shifts is better all | ||
// the way until about `left + right == 32`, but the worst case performance breaks even | ||
|
@@ -175,7 +176,9 @@ unsafe fn ptr_rotate_gcd<T>(left: usize, mid: *mut T, right: usize) { | |
} | ||
} | ||
// finish the chunk with more rounds | ||
for start in 1..gcd { | ||
// FIXME(const-hack): Use `for start in 1..gcd` when available in const | ||
let mut start = 1; | ||
while start < gcd { | ||
// SAFETY: `gcd` is at most equal to `right` so all values in `1..gcd` are valid for | ||
// reading and writing as per the function's safety contract, see [long-safety-expl] | ||
// above | ||
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@@ -201,6 +204,8 @@ unsafe fn ptr_rotate_gcd<T>(left: usize, mid: *mut T, right: usize) { | |
i += right; | ||
} | ||
} | ||
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start += 1; | ||
} | ||
} | ||
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@@ -222,7 +227,7 @@ unsafe fn ptr_rotate_gcd<T>(left: usize, mid: *mut T, right: usize) { | |
/// | ||
/// The specified range must be valid for reading and writing. | ||
#[inline] | ||
unsafe fn ptr_rotate_swap<T>(mut left: usize, mut mid: *mut T, mut right: usize) { | ||
const unsafe fn ptr_rotate_swap<T>(mut left: usize, mut mid: *mut T, mut right: usize) { | ||
loop { | ||
if left >= right { | ||
// Algorithm 3 | ||
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@@ -265,3 +270,8 @@ unsafe fn ptr_rotate_swap<T>(mut left: usize, mut mid: *mut T, mut right: usize) | |
} | ||
} | ||
} | ||
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// FIXME(const-hack): Use cmp::min when available in const | ||
const fn min(left: usize, right: usize) -> usize { | ||
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||
if right < left { right } else { left } | ||
} |
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