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Use unchecked_div/rem

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This commit is contained in:
David Hoppenbrouwers 2022-05-31 08:20:30 +02:00
parent b94e93ead8
commit cb63d7d500
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1 changed files with 9 additions and 8 deletions
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17
library/compiler-builtins/src/mem/x86_64.rs
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@ -16,6 +16,7 @@
// feature is present at compile-time. We don't bother detecting other features.
// Note that ERMSB does not enhance the backwards (DF=1) "rep movsb".
use core::intrinsics;
use core::mem;
#[inline(always)]
@ -110,13 +111,10 @@ pub unsafe fn compare_bytes(a: *const u8, b: *const u8, n: usize) -> i32 {
U: Clone + Copy + Eq,
F: FnOnce(*const U, *const U, usize) -> i32,
{
// Just to be sure we're actually working with powers of two...
let _ = const { 1 - mem::size_of::<T>().count_ones() }; // <= 1
let _ = const { mem::size_of::<T>().count_ones() - 1 }; // >= 1
// Ensure T is not a ZST.
const { assert!(mem::size_of::<T>() != 0) };
// This should be equivalent to division with power-of-two sizes, except the former
// somehow still leaves a call to panic because ??
let end = a.add(n >> mem::size_of::<T>().trailing_zeros());
let end = a.add(intrinsics::unchecked_div(n, mem::size_of::<T>()));
while a != end {
if a.read_unaligned() != b.read_unaligned() {
return f(a.cast(), b.cast(), mem::size_of::<T>());
@ -124,8 +122,11 @@ pub unsafe fn compare_bytes(a: *const u8, b: *const u8, n: usize) -> i32 {
a = a.add(1);
b = b.add(1);
}
// Ditto
f(a.cast(), b.cast(), n & (mem::size_of::<T>() - 1))
f(
a.cast(),
b.cast(),
intrinsics::unchecked_rem(n, mem::size_of::<T>()),
)
}
let c1 = |mut a: *const u8, mut b: *const u8, n| {
for _ in 0..n {