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fixup! Specialize Storage::swap for Row<T>

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Joe Wilm 2018-05-20 16:18:39 -07:00
parent 6eead1f95c
commit 265fc6757d
1 changed files with 7 additions and 9 deletions
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16
src/grid/storage.rs
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@ -46,27 +46,25 @@ impl<T> Swap for Storage<Row<T>> {
/// swap than going through slice::swap.
///
/// The default implementation from swap generates 8 movups and 4 movaps
/// instructions. This implementation only uses 8 movups instructions.
/// instructions. This implementation achieves the swap in only 8 movups
/// instructions.
fn swap(&mut self, a: usize, b: usize) {
use std::mem::{size_of, uninitialized};
use ::libc::memcpy;
debug_assert!(size_of::<Row<T>>() == 32);
debug_assert!(::std::mem::size_of::<Row<T>>() == 32);
let a = self.compute_index(a);
let b = self.compute_index(b);
unsafe {
// Cast to a u64 array of size 4 to pretend that the data is copy
// Cast to a qword array to opt out of copy restrictions and avoid
// drop hazards. Byte array is no good here since for whatever
// reason LLVM won't optimized it.
let a_ptr = self.inner.as_mut_ptr().offset(a as isize) as *mut u64;
let b_ptr = self.inner.as_mut_ptr().offset(b as isize) as *mut u64;
// Swap space
let mut tmp: u64;
// Copy 1 qword at a time
//
// The optimizer unrolls this loop and vectorizes it.
let mut tmp: u64;
for i in 0..4 {
tmp = *a_ptr.offset(i);
*a_ptr.offset(i) = *b_ptr.offset(i);