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add SWAP_BLOCK_SIZE constant

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This commit is contained in:
Djzin 2017-03-13 20:03:10 +00:00
parent d1fec0d87a
commit 1daf589642
1 changed files with 9 additions and 7 deletions
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16
src/libcore/mem.rs
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@ -447,8 +447,10 @@ pub unsafe fn uninitialized<T>() -> T {
#[stable(feature = "rust1", since = "1.0.0")]
pub fn swap<T>(x: &mut T, y: &mut T) {
unsafe {
const SWAP_BLOCK_SIZE: usize = 16;
// Give ourselves some scratch space to work with
let mut t: [u8; 16] = uninitialized();
let mut t: [u8; SWAP_BLOCK_SIZE] = uninitialized();
let x = x as *mut T as *mut u8;
let y = y as *mut T as *mut u8;
@ -457,12 +459,12 @@ pub fn swap<T>(x: &mut T, y: &mut T) {
// can't use a for loop as the `range` impl calls `mem::swap` recursively
let len = size_of::<T>() as isize;
let mut i = 0;
while i + 16 <= len {
// Perform the swap 16 bytes at a time, `&mut` pointers never alias
ptr::copy_nonoverlapping(x.offset(i), t, 16);
ptr::copy_nonoverlapping(y.offset(i), x.offset(i), 16);
ptr::copy_nonoverlapping(t, y.offset(i), 16);
i += 16;
while i + SWAP_BLOCK_SIZE as isize <= len {
// Perform the swap SWAP_BLOCK_SIZE bytes at a time, `&mut` pointers never alias
ptr::copy_nonoverlapping(x.offset(i), t, SWAP_BLOCK_SIZE);
ptr::copy_nonoverlapping(y.offset(i), x.offset(i), SWAP_BLOCK_SIZE);
ptr::copy_nonoverlapping(t, y.offset(i), SWAP_BLOCK_SIZE);
i += SWAP_BLOCK_SIZE as isize;
}
if i < len {
// Swap any remaining bytes