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/*
https://github.com/rust-lang/compiler-builtins/blob/master/compiler-builtins/src/mem/x86_64.rs
*/
#![cfg(target_arch = "x86_64")]
pub mod impls {
use core::arch::{self, asm};
//use core::{intrinsics, mem};
#[inline(always)]
pub unsafe fn copy_forward(dest: *mut u8, src: *const u8, count: usize) {
unsafe {
core::arch::asm!(
"repe movsb (%rsi), (%rdi)",
inout("rcx") count => _,
inout("rdi") dest => _,
inout("rsi") src => _,
options(att_syntax, nostack, preserves_flags)
);
}
}
#[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(dest, count);
// We can't separate this block due to std/cld
unsafe {
asm!(
"std",
"rep movsb",
"sub $7, %rsi",
"sub $7, %rdi",
"mov {qword_count}, %rcx",
"rep movsq",
"test {pre_byte_count:e}, {pre_byte_count:e}",
"add $7, %rsi",
"add $7, %rdi",
"mov {pre_byte_count:e}, %ecx",
"rep movsb",
"cld",
pre_byte_count = in(reg) pre_byte_count,
qword_count = in(reg) qword_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
options(att_syntax, nostack, preserves_flags)
);
}
}
#[inline(always)]
pub unsafe fn set_bytes(dest: *mut u8, c: u8, count: usize) {
// FIXME: Use the Intel syntax once we drop LLVM 9 support on rust-lang/rust.
unsafe {
core::arch::asm!(
"repe stosb %al, (%rdi)",
inout("rcx") count => _,
inout("rdi") dest => _,
inout("al") c => _,
options(att_syntax, nostack, preserves_flags)
)
}
}
/*#[inline(always)]
pub unsafe fn compare_bytes(a: *const u8, b: *const u8, n: usize) -> i32 {
#[inline(always)]
unsafe fn cmp<T, U, F>(mut a: *const T, mut b: *const T, n: usize, f: F) -> i32
where
T: Clone + Copy + Eq,
U: Clone + Copy + Eq,
F: FnOnce(*const U, *const U, usize) -> i32,
{
// Ensure T is not a ZST.
const { assert!(mem::size_of::<T>() != 0) };
let end = unsafe { a.add(intrinsics::unchecked_div(n, mem::size_of::<T>())) };
while a != end {
if unsafe { a.read_unaligned() != b.read_unaligned() }{
return f(a.cast(), b.cast(), mem::size_of::<T>());
}
a = unsafe { a.add(1) };
b = unsafe { b.add(1) };
}
f(
a.cast(),
b.cast(),
unsafe { intrinsics::unchecked_rem(n, mem::size_of::<T>()) },
)
}
let c1 = |mut a: *const u8, mut b: *const u8, n| {
for _ in 0..n {
if unsafe { a.read() != b.read() }{
return unsafe { i32::from(a.read()) - i32::from(b.read())};
}
a = unsafe { a.add(1) };
b = unsafe { b.add(1) };
}
0
};
let c2 = |a: *const u16, b, n| unsafe { cmp(a, b, n, c1) };
let c4 = |a: *const u32, b, n| unsafe { cmp(a, b, n, c2) };
let c8 = |a: *const u64, b, n| unsafe { cmp(a, b, n, c4) };
let c16 = |a: *const u128, b, n| unsafe { cmp(a, b, n, c8) };
c16(a.cast(), b.cast(), n)
}*/
fn rep_param(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 = ((8 - (dest as usize & 0b111)) & 0b111).min(count);
count -= pre_byte_count;
let qword_count = count >> 3;
let byte_count = count & 0b111;
(pre_byte_count, qword_count, byte_count)
}
#[inline(always)]
pub unsafe fn c_string_length(mut s: *const core::ffi::c_char) -> usize {
use core::arch::x86_64::{__m128i, _mm_cmpeq_epi8, _mm_movemask_epi8, _mm_set1_epi8};
let mut n = 0;
// The use of _mm_movemask_epi8 and company allow for speedups,
// but they aren't cheap by themselves. Thus, possibly small strings
// are handled in simple loops.
for _ in 0..4 {
if unsafe { *s } == 0 {
return n;
}
n += 1;
s = unsafe { s.add(1) };
}
// Shave of the least significand bits to align the address to a 16
// byte boundary. The shaved of bits are used to correct the first iteration.
let align = s as usize & 15;
let mut s = ((s as usize) - align) as *const __m128i;
let zero = unsafe { _mm_set1_epi8(0) };
let x = {
let r;
unsafe {
arch::asm!(
"movdqa ({addr}), {dest}",
addr = in(reg) s,
dest = out(xmm_reg) r,
options(att_syntax, nostack),
);
}
r
};
let cmp = unsafe { _mm_movemask_epi8(_mm_cmpeq_epi8(x, zero)) } >> align;
if cmp != 0 {
return n + cmp.trailing_zeros() as usize;
}
n += 16 - align;
s = unsafe { s.add(1) };
loop {
let x = {
let r;
unsafe {
arch::asm!(
"movdqa ({addr}), {dest}",
addr = in(reg) s,
dest = out(xmm_reg) r,
options(att_syntax, nostack),
);
}
r
};
let cmp = unsafe { _mm_movemask_epi8(_mm_cmpeq_epi8(x, zero)) } as u32;
if cmp == 0 {
n += 16;
s = unsafe { s.add(1) };
} else {
return n + cmp.trailing_zeros() as usize;
}
}
}
}