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Remove rep_param_rev

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David Hoppenbrouwers 2022-07-07 13:13:19 +02:00
parent 45e2996c96
commit 897a133869
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1 changed files with 4 additions and 14 deletions
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18
library/compiler-builtins/src/mem/x86_64.rs
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@ -69,7 +69,7 @@ pub unsafe fn copy_forward(mut dest: *mut u8, mut src: *const u8, count: usize)
#[inline(always)]
pub unsafe fn copy_backward(dest: *mut u8, src: *const u8, count: usize) {
let (pre_byte_count, qword_count, byte_count) = rep_param_rev(dest, count);
let (pre_byte_count, qword_count, byte_count) = rep_param(dest, count);
// We can't separate this block due to std/cld
asm!(
"std",
@ -80,12 +80,12 @@ pub unsafe fn copy_backward(dest: *mut u8, src: *const u8, count: usize) {
"rep movsq",
"add rsi, 7",
"add rdi, 7",
"mov ecx, {byte_count:e}",
"mov ecx, {pre_byte_count:e}",
"rep movsb",
"cld",
byte_count = in(reg) byte_count,
pre_byte_count = in(reg) pre_byte_count,
qword_count = in(reg) qword_count,
inout("ecx") pre_byte_count => _,
inout("ecx") byte_count => _,
inout("rdi") dest.add(count - 1) => _,
inout("rsi") src.add(count - 1) => _,
// We modify flags, but we restore it afterwards
@ -205,13 +205,3 @@ fn rep_param(dest: *mut u8, mut count: usize) -> (usize, usize, usize) {
let byte_count = count & 0b111;
(pre_byte_count, qword_count, byte_count)
}
/// Determine optimal parameters for a reverse `rep` instruction (i.e. direction bit is set).
fn rep_param_rev(dest: *mut u8, mut count: usize) -> (usize, usize, usize) {
// Unaligned writes are still slow on modern processors, so align the destination address.
let pre_byte_count = ((dest as usize + count) & 0b111).min(count);
count -= pre_byte_count;
let qword_count = count >> 3;
let byte_count = count & 0b111;
(pre_byte_count, qword_count, byte_count)
}