Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Use MaybeUninit in DecInt #1201

Merged
merged 8 commits into from
Nov 21, 2024
Merged
Show file tree
Hide file tree
Changes from 6 commits
Commits
File filter

Filter by extension

Filter by extension


Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion Cargo.toml
Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ rust-version = "1.63"

[dependencies]
bitflags = { version = "2.4.0", default-features = false }
itoa = { version = "1.0.1", default-features = false, optional = true }
itoa = { version = "1.0.12", default-features = false, optional = true }

# Special dependencies used in rustc-dep-of-std mode.
core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }
Expand Down
70 changes: 38 additions & 32 deletions src/path/dec_int.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@

use crate::backend::fd::{AsFd, AsRawFd};
use crate::ffi::CStr;
use core::fmt::Write;
use core::mem::{self, MaybeUninit};
use itoa::{Buffer, Integer};
#[cfg(all(feature = "std", unix))]
use std::os::unix::ffi::OsStrExt;
Expand Down Expand Up @@ -36,23 +36,38 @@ use {core::fmt, std::ffi::OsStr, std::path::Path};
/// ```
#[derive(Clone)]
pub struct DecInt {
// 20 `u8`s is enough to hold the decimal ASCII representation of any
// `u64`, and we add one for a NUL terminator for `as_c_str`.
buf: [u8; 20 + 1],
// Enough to hold an {u,i}64 and NUL terminator.
buf: [MaybeUninit<u8>; u64::MAX_STR_LEN + 1],
len: usize,
}
const _: () = assert!(u64::MAX_STR_LEN == i64::MAX_STR_LEN);

impl DecInt {
/// Construct a new path component from an integer.
#[inline]
pub fn new<Int: Integer>(i: Int) -> Self {
let mut me = DecIntWriter(Self {
buf: [0; 20 + 1],
len: 0,
});
let mut buf = Buffer::new();
me.write_str(buf.format(i)).unwrap();
me.0
pub fn new<Int: Integer + 'static>(i: Int) -> Self {
let mut buf = [MaybeUninit::uninit(); 21];

let mut str_buf = Buffer::new();
let str_buf = str_buf.format(i);
{
SUPERCILEX marked this conversation as resolved.
Show resolved Hide resolved
assert!(
str_buf.len() < buf.len(),
"{str_buf}{} unsupported.",
core::any::type_name::<Int>()
);

buf[..str_buf.len()].copy_from_slice(unsafe {
// SAFETY: you can always go from init to uninit
mem::transmute::<&[u8], &[MaybeUninit<u8>]>(str_buf.as_bytes())
});
buf[str_buf.len()] = MaybeUninit::new(0);
}

Self {
buf,
len: str_buf.len(),
}
}

/// Construct a new path component from a file descriptor.
Expand All @@ -72,44 +87,35 @@ impl DecInt {
/// Return the raw byte buffer as a `&CStr`.
#[inline]
pub fn as_c_str(&self) -> &CStr {
let bytes_with_nul = &self.buf[..=self.len];
let bytes_with_nul = self.as_bytes_with_nul();
debug_assert!(CStr::from_bytes_with_nul(bytes_with_nul).is_ok());

// SAFETY: `self.buf` holds a single decimal ASCII representation and
// at least one extra NUL byte.
unsafe { CStr::from_bytes_with_nul_unchecked(bytes_with_nul) }
}

/// Return the raw byte buffer.
/// Return the raw byte buffer including the NUL byte.
#[inline]
pub fn as_bytes(&self) -> &[u8] {
&self.buf[..self.len]
pub fn as_bytes_with_nul(&self) -> &[u8] {
let init = &self.buf[..=self.len];
// SAFETY: we're guaranteed to have initialized len+1 bytes.
unsafe { mem::transmute::<&[MaybeUninit<u8>], &[u8]>(init) }
}
}

/// A wrapper around `DecInt` that implements `Write` without exposing this
/// implementation to `DecInt`'s public API.
struct DecIntWriter(DecInt);

impl core::fmt::Write for DecIntWriter {
/// Return the raw byte buffer.
#[inline]
fn write_str(&mut self, s: &str) -> core::fmt::Result {
match self.0.buf.get_mut(self.0.len..self.0.len + s.len()) {
Some(slice) => {
slice.copy_from_slice(s.as_bytes());
self.0.len += s.len();
Ok(())
}
None => Err(core::fmt::Error),
}
pub fn as_bytes(&self) -> &[u8] {
let bytes = self.as_bytes_with_nul();
&bytes[..bytes.len() - 1]
}
}

#[cfg(feature = "std")]
impl AsRef<Path> for DecInt {
#[inline]
fn as_ref(&self) -> &Path {
let as_os_str: &OsStr = OsStrExt::from_bytes(&self.buf[..self.len]);
let as_os_str: &OsStr = OsStrExt::from_bytes(self.as_bytes());
Path::new(as_os_str)
}
}
Expand Down
50 changes: 35 additions & 15 deletions tests/path/dec_int.rs
Original file line number Diff line number Diff line change
@@ -1,20 +1,40 @@
use rustix::path::DecInt;

macro_rules! check {
($i:expr) => {
let i = $i;
assert_eq!(DecInt::new(i).as_ref().to_str().unwrap(), i.to_string());
};
}

#[test]
fn test_dec_int() {
assert_eq!(DecInt::new(0).as_ref().to_str().unwrap(), "0");
assert_eq!(DecInt::new(-1).as_ref().to_str().unwrap(), "-1");
assert_eq!(DecInt::new(789).as_ref().to_str().unwrap(), "789");
assert_eq!(
DecInt::new(i64::MIN).as_ref().to_str().unwrap(),
i64::MIN.to_string()
);
assert_eq!(
DecInt::new(i64::MAX).as_ref().to_str().unwrap(),
i64::MAX.to_string()
);
assert_eq!(
DecInt::new(u64::MAX).as_ref().to_str().unwrap(),
u64::MAX.to_string()
);
check!(0);
check!(-1);
check!(789);

check!(u8::MAX);
check!(i8::MIN);
check!(u16::MAX);
check!(i16::MIN);
check!(u32::MAX);
check!(i32::MIN);
check!(u64::MAX);
check!(i64::MIN);
#[cfg(any(
target_pointer_width = "16",
target_pointer_width = "32",
target_pointer_width = "64"
))]
{
check!(usize::MAX);
check!(isize::MIN);
}
}

#[test]
#[should_panic]
fn test_unsupported_dec_int() {
check!(u128::MAX);
check!(i128::MIN);
}
SUPERCILEX marked this conversation as resolved.
Show resolved Hide resolved