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//! `imp_x86` has specialized copies to append short strings to strings. buffer sizing must be
//! handled by callers, in all cases.
//!
//! the structure of all implementations here is, essentially, to take the size of the data to
//! append and execute a copy for each bit set in that size, from highest to lowest. some bits are
//! simply never checked if the input is promised to never be that large - if a string to append is
//! only 0..7 bytes long, it is sufficient to only look at the low three bits to copy all bytes.
//!
//! in this way, it is slightly more efficient to right-size which append function is used, if the
//! maximum size of input strings can be bounded well. if the maximum size of input strings cannot
//! be bounded, you shouldn't be using these functions.
/// append `data` to `buf`, assuming `data` is less than 8 bytes and that `buf` has enough space
/// remaining to hold all bytes in `data`.
///
/// Safety: callers must ensure that `buf.capacity() - buf.len() >= data.len()`.
#[inline(always)]
pub unsafe fn append_string_lt_8_unchecked(buf: &mut alloc::string::String, data: &str) {
// Safety: we are appending only valid utf8 strings to `self.buf`, as `s` is known to
// be valid utf8
let buf = unsafe { buf.as_mut_vec() };
let new_bytes = data.as_bytes();
unsafe {
let dest = buf.as_mut_ptr().offset(buf.len() as isize);
let src = new_bytes.as_ptr();
let rem = new_bytes.len() as isize;
// set_len early because there is no way to avoid the following asm!() writing that
// same number of bytes into buf
buf.set_len(buf.len() + new_bytes.len());
core::arch::asm!(
"8:",
"cmp {rem:e}, 4",
"jb 9f",
"mov {buf:e}, dword ptr [{src} + {rem} - 4]",
"mov dword ptr [{dest} + {rem} - 4], {buf:e}",
"sub {rem:e}, 4",
"jz 11f",
"9:",
"cmp {rem:e}, 2",
"jb 10f",
"mov {buf:x}, word ptr [{src} + {rem} - 2]",
"mov word ptr [{dest} + {rem} - 2], {buf:x}",
"sub {rem:e}, 2",
"jz 11f",
"10:",
"cmp {rem:e}, 1",
"jb 11f",
"mov {buf:l}, byte ptr [{src} + {rem} - 1]",
"mov byte ptr [{dest} + {rem} - 1], {buf:l}",
"11:",
src = in(reg) src,
dest = in(reg) dest,
rem = inout(reg) rem => _,
buf = out(reg) _,
options(nostack),
);
}
}
/// append `data` to `buf`, assuming `data` is less than 16 bytes and that `buf` has enough space
/// remaining to hold all bytes in `data`.
///
/// Safety: callers must ensure that `buf.capacity() - buf.len() >= data.len()`.
#[inline(always)]
pub unsafe fn append_string_lt_16_unchecked(buf: &mut alloc::string::String, data: &str) {
// Safety: we are appending only valid utf8 strings to `self.buf`, as `s` is known to
// be valid utf8
let buf = unsafe { buf.as_mut_vec() };
let new_bytes = data.as_bytes();
unsafe {
let dest = buf.as_mut_ptr().offset(buf.len() as isize);
let src = new_bytes.as_ptr();
let rem = new_bytes.len() as isize;
// set_len early because there is no way to avoid the following asm!() writing that
// same number of bytes into buf
buf.set_len(buf.len() + new_bytes.len());
core::arch::asm!(
"7:",
"cmp {rem:e}, 8",
"jb 8f",
"mov {buf:r}, qword ptr [{src} + {rem} - 8]",
"mov qword ptr [{dest} + {rem} - 8], {buf:r}",
"sub {rem:e}, 8",
"jz 11f",
"8:",
"cmp {rem:e}, 4",
"jb 9f",
"mov {buf:e}, dword ptr [{src} + {rem} - 4]",
"mov dword ptr [{dest} + {rem} - 4], {buf:e}",
"sub {rem:e}, 4",
"jz 11f",
"9:",
"cmp {rem:e}, 2",
"jb 10f",
"mov {buf:x}, word ptr [{src} + {rem} - 2]",
"mov word ptr [{dest} + {rem} - 2], {buf:x}",
"sub {rem:e}, 2",
"jz 11f",
"10:",
"cmp {rem:e}, 1",
"jb 11f",
"mov {buf:l}, byte ptr [{src} + {rem} - 1]",
"mov byte ptr [{dest} + {rem} - 1], {buf:l}",
"11:",
src = in(reg) src,
dest = in(reg) dest,
rem = inout(reg) rem => _,
buf = out(reg) _,
options(nostack),
);
}
}
/// append `data` to `buf`, assuming `data` is less than 32 bytes and that `buf` has enough space
/// remaining to hold all bytes in `data`.
///
/// Safety: callers must ensure that `buf.capacity() - buf.len() >= data.len()`.
#[inline(always)]
pub unsafe fn append_string_lt_32_unchecked(buf: &mut alloc::string::String, data: &str) {
// Safety: we are appending only valid utf8 strings to `self.buf`, as `s` is known to
// be valid utf8
let buf = unsafe { buf.as_mut_vec() };
let new_bytes = data.as_bytes();
unsafe {
let dest = buf.as_mut_ptr().offset(buf.len() as isize);
let src = new_bytes.as_ptr();
let rem = new_bytes.len() as isize;
// set_len early because there is no way to avoid the following asm!() writing that
// same number of bytes into buf
buf.set_len(buf.len() + new_bytes.len());
core::arch::asm!(
"6:",
"cmp {rem:e}, 16",
"jb 7f",
"mov {buf:r}, qword ptr [{src} + {rem} - 16]",
"mov qword ptr [{dest} + {rem} - 16], {buf:r}",
"mov {buf:r}, qword ptr [{src} + {rem} - 8]",
"mov qword ptr [{dest} + {rem} - 8], {buf:r}",
"sub {rem:e}, 16",
"jz 11f",
"7:",
"cmp {rem:e}, 8",
"jb 8f",
"mov {buf:r}, qword ptr [{src} + {rem} - 8]",
"mov qword ptr [{dest} + {rem} - 8], {buf:r}",
"sub {rem:e}, 8",
"jz 11f",
"8:",
"cmp {rem:e}, 4",
"jb 9f",
"mov {buf:e}, dword ptr [{src} + {rem} - 4]",
"mov dword ptr [{dest} + {rem} - 4], {buf:e}",
"sub {rem:e}, 4",
"jz 11f",
"9:",
"cmp {rem:e}, 2",
"jb 10f",
"mov {buf:x}, word ptr [{src} + {rem} - 2]",
"mov word ptr [{dest} + {rem} - 2], {buf:x}",
"sub {rem:e}, 2",
"jz 11f",
"10:",
"cmp {rem:e}, 1",
"jb 11f",
"mov {buf:l}, byte ptr [{src} + {rem} - 1]",
"mov byte ptr [{dest} + {rem} - 1], {buf:l}",
"11:",
src = in(reg) src,
dest = in(reg) dest,
rem = inout(reg) rem => _,
buf = out(reg) _,
options(nostack),
);
}
}
|
