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605 lines
20 KiB
Rust
605 lines
20 KiB
Rust
use core::{
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borrow,
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cmp::Ordering,
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fmt,
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hash::{Hash, Hasher},
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mem::MaybeUninit,
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ops, ptr, str,
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};
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#[cfg(not(feature = "std"))]
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use core::convert::TryFrom;
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#[cfg(all(feature = "alloc", not(feature = "std")))]
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use alloc::{
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borrow::{Cow, ToOwned},
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boxed::Box,
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string::String,
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};
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#[cfg(feature = "std")]
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use std::borrow::Cow;
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#[derive(Debug)]
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pub struct CapacityError;
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impl fmt::Display for CapacityError {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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write!(f, "`CappedString` capacity exceeded")
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}
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}
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#[cfg(feature = "std")]
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impl std::error::Error for CapacityError {}
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/// A string type which stores at most `N` bytes of string data. The string data is stored inline
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/// rather than using a heap allocation.
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///
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/// ```
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/// # use libshire::strings::CappedString;
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/// # fn main() -> Result<(), libshire::strings::capped::Error> {
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/// let s = CappedString::<16>::new("hello world")?;
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/// assert_eq!(&*s, "hello world");
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/// # Ok(())
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/// # }
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/// ```
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#[derive(Clone)]
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pub struct CappedString<const N: usize> {
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buf: [MaybeUninit<u8>; N],
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len: u8,
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}
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impl<const N: usize> CappedString<N> {
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const MAX_LEN: u8 = {
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#[allow(clippy::cast_possible_truncation, clippy::checked_conversions)]
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if N <= u8::MAX as usize {
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N as u8
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} else {
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panic!("`N` must be within the bounds of `u8`")
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}
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};
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/// Creates a new `CappedString` from a given byte buffer and length.
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///
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/// # Safety
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/// The first `len` bytes of `buf` (i.e. `buf[..len]`) must be initialised and valid UTF-8.
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/// `len` must be less than or equal to `N`.
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#[inline]
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#[must_use]
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pub const unsafe fn from_raw_parts(buf: [MaybeUninit<u8>; N], len: u8) -> Self {
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Self { buf, len }
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}
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#[inline]
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#[must_use]
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pub const fn into_raw_parts(self) -> ([MaybeUninit<u8>; N], u8) {
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(self.buf, self.len)
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}
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/// # Safety
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/// `src` must point to `len` bytes of valid, UTF-8 string data. `len` must be less than or
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/// equal to `N`.
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#[inline]
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unsafe fn from_raw_ptr(src: *const u8, len: u8) -> Self {
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// `u8` has the same memory layout as `MaybeUninit<u8>`, so this cast is valid.
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let src = src as *const MaybeUninit<u8>;
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// SAFETY:
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// `MaybeUninit::uninit()` is a valid value for `[MaybeUninit<u8>; N]`, since each element
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// of the array is allowed to be uninitialised.
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let mut buf = unsafe { MaybeUninit::<[MaybeUninit<u8>; N]>::uninit().assume_init() };
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// SAFETY:
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// The caller is responsible for ensuring that `src` points to a valid string, which means
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// that it must not overlap with the new local variable `buf`. The caller is responsible
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// for ensuring that `src` is valid for reads of `len` bytes. The caller is responsible for
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// ensuring that `len <= N`, so `buf` is valid for writes of `len` bytes. `src` and `buf`
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// are both trivially properly aligned, since they both have an alignment of 1.
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unsafe { ptr::copy_nonoverlapping(src, buf.as_mut_ptr(), usize::from(len)); }
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// SAFETY:
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// The caller is responsible for ensuring that `src` points to `len` bytes of valid UTF-8
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// data. `src` is copied into the start of `buf`, so the first `len` bytes of `buf` are
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// valid UTF-8. The caller is responsible for ensuring that `len <= N`.
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unsafe { Self::from_raw_parts(buf, len) }
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}
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/// # Safety
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/// `self.len` must be less than `N`, so that there is space in the buffer to append the byte.
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#[inline]
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unsafe fn append_byte(&mut self, byte: u8) {
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// SAFETY:
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// The caller is responsible for ensuring that `self.len < N`.
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let dst = unsafe { self.buf.get_unchecked_mut(usize::from(self.len)) };
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*dst = MaybeUninit::new(byte);
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self.len += 1;
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}
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/// # Safety
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/// `src` must point to `len` bytes of valid UTF-8 string data. `len` must be less than or equal
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/// to `N - self.len`.
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#[inline]
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unsafe fn append_bytes(&mut self, src: *const u8, len: u8) {
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// `u8` has the same memory layout as `MaybeUninit<u8>`, so this cast is valid.
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let src = src as *const MaybeUninit<u8>;
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// SAFETY:
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// `self.len <= N` is an invariant of `CappedString`, so `self.len..` is a valid range over
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// `self.buf`.
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let dst = unsafe { self.buf.get_unchecked_mut(usize::from(self.len)..) };
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// SAFETY:
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// The caller is responsible for ensuring that `src` points to a valid string, which means
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// that it cannot overlap with the new local variable `buf`. The caller is responsible for
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// ensuring that `src` is valid for reads of `len` bytes. The caller is responsible for
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// ensuring that `len <= N - self.len`, so the destination `dst = self.buf[self.len..]` is
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// valid for writes of `len` bytes. `src` and `dst` are both trivially properly aligned,
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// since they both have an alignment of 1.
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unsafe { ptr::copy_nonoverlapping(src, dst.as_mut_ptr(), usize::from(len)); }
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self.len += len;
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}
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/// Returns a new empty `CappedString`.
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///
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/// ```
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/// # use libshire::strings::CappedString;
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/// let s = CappedString::<8>::empty();
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/// assert!(s.is_empty());
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/// assert_eq!(s.len(), 0);
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/// assert_eq!(&*s, "");
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/// ```
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#[inline]
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#[must_use]
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pub const fn empty() -> Self {
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// SAFETY:
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// `MaybeUninit::uninit()` is a valid value for `[MaybeUninit<u8>; N]`, since each element
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// of the array is allowed to be uninitialised.
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let buf = unsafe { MaybeUninit::<[MaybeUninit<u8>; N]>::uninit().assume_init() };
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// SAFETY:
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// It is vacuously true that the first 0 bytes of the buffer are initialised and valid
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// UTF-8.
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unsafe { Self::from_raw_parts(buf, 0) }
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}
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/// Returns a new `CappedString` containing the given string data. The string data will be
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/// stored inline; no heap allocation is used. An error will be returned if the length of the
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/// provided string exceeds the `CappedString`'s maximum length, `N`.
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///
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/// ```
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/// # use libshire::strings::CappedString;
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/// # fn main() -> Result<(), libshire::strings::capped::Error> {
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/// let s = CappedString::<16>::new("hello world")?;
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/// assert_eq!(&*s, "hello world");
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/// # Ok(())
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/// # }
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/// ```
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#[inline]
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pub fn new<S>(src: &S) -> Result<Self, CapacityError>
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where
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S: AsRef<str> + ?Sized,
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{
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// Convert the string to a byte slice, which is guaranteed to be valid UTF-8 since this is
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// an invariant of `str`.
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let src = <S as AsRef<str>>::as_ref(src);
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// If the length of the `src` string does not fit into a `u8` or is greater than
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// `Self::MAX_LEN`, we can't fit it into the new `CappedString` so return an error.
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let len = match u8::try_from(src.len()) {
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Ok(len) if len <= Self::MAX_LEN => len,
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_ => return Err(CapacityError),
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};
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// SAFETY:
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// `src.as_ptr()` points to `len` bytes of valid UTF-8 string data since `src` is a `&str`
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// and `len` is its length. `len` is less than or equal to `Self::MAX_LEN`, which is equal
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// to `N`.
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unsafe { Ok(Self::from_raw_ptr(src.as_ptr(), len)) }
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}
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#[inline]
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#[must_use]
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pub fn new_truncating<S>(src: &S) -> Self
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where
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S: AsRef<str> + ?Sized,
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{
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let src = <S as AsRef<str>>::as_ref(src);
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let (src, len) = truncate_str(src, Self::MAX_LEN);
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// SAFETY:
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// It is part of the contract of `truncate_str` that it returns a pointer to a valid UTF-8
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// string of length `len`, and that `len` is less than or equal to the provided maximum
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// length, which is `Self::MAX_LEN` (which is equal to `N`) in this case.
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unsafe { Self::from_raw_ptr(src, len) }
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}
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/// Appends the given character to the end of this `CappedString`, returning an error if there
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/// is insufficient capacity remaining to do so.
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///
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/// If you do not care whether or not the append succeeds, see [`Self::push_truncating`].
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#[inline]
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pub fn push(&mut self, c: char) -> Result<(), CapacityError> {
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let mut char_buf = [0u8; 4];
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let encoded = c.encode_utf8(&mut char_buf);
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match encoded.len() {
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1 => {
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if self.len == Self::MAX_LEN {
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return Err(CapacityError);
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}
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// SAFETY:
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//
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unsafe { self.append_byte(encoded.as_bytes()[0]) }
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Ok(())
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},
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_ => self.push_str(encoded),
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}
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}
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/// Appends the given character to the end of this `CappedString`, failing silently if there is
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/// insufficient capacity remaining to do so.
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///
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/// If you would like to know whether or not the append succeeds, see [`Self::push`].
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#[inline]
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pub fn push_truncating(&mut self, c: char) {
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// Unlike `Self::push_str_truncating`, we can just use `Self::push` and swallow the error
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// because a single character will never be partially pushed; it is either pushed or it
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// isn't.
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self.push(c).ok();
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}
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/// Appends the given string slice to the end of this `CappedString`, returning an error if
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/// there is insufficient capacity remaining to do so.
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///
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/// If you would like a version which cannot fail, see [`Self::push_str_truncating`].
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#[inline]
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pub fn push_str<S>(&mut self, src: &S) -> Result<(), CapacityError>
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where
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S: AsRef<str> + ?Sized,
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{
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let src = <S as AsRef<str>>::as_ref(src);
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let len = match u8::try_from(src.len()) {
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Ok(len) if len <= Self::MAX_LEN - self.len => len,
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_ => return Err(CapacityError),
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};
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// SAFETY:
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// `src` is a valid string slice with length `len`. We have checked that
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// `len <= N - self.len` holds above (note that `Self::MAX_LEN == N`).
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unsafe { self.append_bytes(src.as_ptr(), len); }
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Ok(())
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}
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/// Appends as many of the characters of the given string slice to the end of this
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/// `CappedString` as can fit. Any remaining characters will not be added.
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///
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/// If you would like a version which returns an error if there is not enough capacity remaining
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/// to append the entire string slice, see [`Self::push_str`].
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#[inline]
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pub fn push_str_truncating<S>(&mut self, src: &S)
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where
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S: AsRef<str> + ?Sized,
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{
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let remaining_cap = Self::MAX_LEN - self.len;
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// Short-circuit if we have no space left to copy into.
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if remaining_cap == 0 {
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return;
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}
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let src = <S as AsRef<str>>::as_ref(src);
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// Find the longest valid UTF-8 prefix which fits into the remaining space.
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let (src, len) = truncate_str(src, remaining_cap);
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// SAFETY:
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// `truncate_str` returns a pointer to `len` bytes of valid UTF-8 string data. The returned
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// `len` will always be less than or equal to `remaining_cap`, which is equal to
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// `N - self.len` (note that `Self::MAX_LEN == N`).
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unsafe { self.append_bytes(src, len); }
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}
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/// Returns a string slice pointing to the underlying string data.
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#[inline]
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#[must_use]
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pub fn as_str(&self) -> &str {
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// SAFETY:
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// The first `self.len` bytes of `self.buf` (which is returned by `Self::as_bytes`) being
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// valid UTF-8 is an invariant of `CappedString`.
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unsafe { str::from_utf8_unchecked(self.as_bytes()) }
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}
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/// Returns a mutable string slice pointing to the underlying string data.
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#[inline]
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#[must_use]
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pub fn as_str_mut(&mut self) -> &mut str {
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// SAFETY:
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// The first `self.len` bytes of `self.buf` (which is returned by `Self::as_bytes_mut`)
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// being valid UTF-8 is an invariant of `CappedString`.
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unsafe { str::from_utf8_unchecked_mut(self.as_bytes_mut()) }
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}
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#[inline]
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#[must_use]
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pub fn as_bytes(&self) -> &[u8] {
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// Get the slice of the buffer containing initialised string data.
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// SAFETY:
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// It is an invariant of `CappedString` that `self.len <= N`, so `..self.len` is a valid
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// range over `self.buf`.
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let data_slice = unsafe { self.buf.get_unchecked(..usize::from(self.len)) };
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// Convert the `&[MaybeUninit<u8>]` to a `&[u8]`.
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// SAFETY:
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// `MaybeUninit<u8>` has the same memory layout as `u8`, and the first `self.len` bytes of
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// the buffer are initialised, so this conversion is valid.
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unsafe { &*(data_slice as *const [MaybeUninit<u8>] as *const [u8]) }
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}
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/// # Safety
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/// The caller is responsible for ensuring that the slice is valid UTF-8 when the mutable
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/// borrow ends.
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#[inline]
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#[must_use]
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pub unsafe fn as_bytes_mut(&mut self) -> &mut [u8] {
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// Get the slice of the buffer containing initialised string data.
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// SAFETY:
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// It is an invariant of `CappedString` that `self.len <= N`, so `..self.len` is a valid
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// range over `self.buf`.
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let data_slice = unsafe { self.buf.get_unchecked_mut(..usize::from(self.len)) };
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// Convert the `&[MaybeUninit<u8>]` to a `&[u8]`.
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// SAFETY:
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// `MaybeUninit<u8>` has the same memory layout as `u8`, and the first `self.len` bytes of
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// the buffer are initialised, so this conversion is valid.
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unsafe { &mut *(data_slice as *mut [MaybeUninit<u8>] as *mut [u8]) }
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}
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#[inline]
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#[must_use]
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pub fn len(&self) -> usize {
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usize::from(self.len)
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}
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#[inline]
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#[must_use]
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pub fn is_empty(&self) -> bool {
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self.len == 0
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}
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}
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#[cfg(feature = "alloc")]
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impl<const N: usize> CappedString<N> {
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#[inline]
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#[must_use]
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pub fn into_boxed_str(self) -> Box<str> {
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self.as_str().into()
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}
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#[inline]
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#[must_use]
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pub fn into_string(self) -> String {
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self.as_str().to_owned()
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}
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}
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impl<const N: usize> Default for CappedString<N> {
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#[inline]
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fn default() -> Self {
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Self::empty()
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}
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}
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impl<const N: usize> ops::Deref for CappedString<N> {
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type Target = str;
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#[inline]
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fn deref(&self) -> &Self::Target {
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self.as_str()
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}
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}
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impl<const N: usize> ops::DerefMut for CappedString<N> {
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#[inline]
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fn deref_mut(&mut self) -> &mut Self::Target {
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self.as_str_mut()
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}
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}
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impl<const N: usize> AsRef<str> for CappedString<N> {
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#[inline]
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fn as_ref(&self) -> &str {
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self
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}
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}
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impl<const N: usize> AsMut<str> for CappedString<N> {
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#[inline]
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fn as_mut(&mut self) -> &mut str {
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self
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}
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}
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impl<const N: usize> borrow::Borrow<str> for CappedString<N> {
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#[inline]
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fn borrow(&self) -> &str {
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self
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}
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}
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impl<const N: usize> borrow::BorrowMut<str> for CappedString<N> {
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#[inline]
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fn borrow_mut(&mut self) -> &mut str {
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self
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}
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}
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impl<'a, const N: usize> TryFrom<&'a str> for CappedString<N> {
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type Error = CapacityError;
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#[inline]
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fn try_from(s: &'a str) -> Result<Self, Self::Error> {
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Self::new(s)
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}
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}
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|
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#[cfg(feature = "alloc")]
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impl<const N: usize> TryFrom<String> for CappedString<N> {
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type Error = CapacityError;
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|
|
#[inline]
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fn try_from(s: String) -> Result<Self, Self::Error> {
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Self::new(&s)
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}
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}
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|
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#[cfg(feature = "alloc")]
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impl<const N: usize> TryFrom<Box<str>> for CappedString<N> {
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type Error = CapacityError;
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|
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#[inline]
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fn try_from(s: Box<str>) -> Result<Self, Self::Error> {
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Self::new(&s)
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}
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}
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|
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#[cfg(feature = "alloc")]
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impl<'a, const N: usize> TryFrom<Cow<'a, str>> for CappedString<N> {
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type Error = CapacityError;
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|
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#[inline]
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fn try_from(s: Cow<'a, str>) -> Result<Self, Self::Error> {
|
|
Self::new(&s)
|
|
}
|
|
}
|
|
|
|
#[cfg(feature = "alloc")]
|
|
impl<const N: usize> From<CappedString<N>> for String {
|
|
#[inline]
|
|
fn from(s: CappedString<N>) -> Self {
|
|
s.into_string()
|
|
}
|
|
}
|
|
|
|
#[cfg(feature = "alloc")]
|
|
impl<const N: usize> From<CappedString<N>> for Box<str> {
|
|
#[inline]
|
|
fn from(s: CappedString<N>) -> Self {
|
|
s.into_boxed_str()
|
|
}
|
|
}
|
|
|
|
impl<const N: usize, const M: usize> PartialEq<CappedString<M>> for CappedString<N> {
|
|
#[inline]
|
|
fn eq(&self, other: &CappedString<M>) -> bool {
|
|
**self == **other
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> Eq for CappedString<N> {}
|
|
|
|
impl<const N: usize, const M: usize> PartialOrd<CappedString<M>> for CappedString<N> {
|
|
#[inline]
|
|
fn partial_cmp(&self, other: &CappedString<M>) -> Option<Ordering> {
|
|
(**self).partial_cmp(&**other)
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> Ord for CappedString<N> {
|
|
#[inline]
|
|
fn cmp(&self, other: &Self) -> Ordering {
|
|
(**self).cmp(&**other)
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> Hash for CappedString<N> {
|
|
#[inline]
|
|
fn hash<H: Hasher>(&self, state: &mut H) {
|
|
(**self).hash(state);
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> str::FromStr for CappedString<N> {
|
|
type Err = CapacityError;
|
|
|
|
#[inline]
|
|
fn from_str(s: &str) -> Result<Self, Self::Err> {
|
|
Self::new(s)
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> fmt::Debug for CappedString<N> {
|
|
#[inline]
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Debug::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
impl<const N: usize> fmt::Display for CappedString<N> {
|
|
#[inline]
|
|
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
|
|
fmt::Display::fmt(&**self, f)
|
|
}
|
|
}
|
|
|
|
/// Returns a pointer to the longest prefix of `src` which is valid UTF-8 and whose length is
|
|
/// less than or equal to `max_len`, and returns the length of this prefix.
|
|
#[inline]
|
|
fn truncate_str(src: &str, max_len: u8) -> (*const u8, u8) {
|
|
match u8::try_from(src.len()) {
|
|
// If the length of the `src` string is less than or equal to `max_len`, there is no need to
|
|
// truncate it.
|
|
Ok(src_len) if src_len <= max_len => (src.as_ptr(), src_len),
|
|
|
|
// If the length of `src` is greater than `max_len`, we need to truncate it. Note that
|
|
// `u8::try_from` returning an error means that `src.len() > max_len`, since `max_len` is a
|
|
// `u8` and `src.len()` is a `usize`.
|
|
_ => {
|
|
let src = src.as_bytes();
|
|
|
|
let mut i = max_len;
|
|
|
|
// Find the rightmost codepoint which starts at an index less than or equal to
|
|
// `max_len`. Everything to the left of this will be valid UTF-8 with a length less
|
|
// than or equal to `max_len`. We only need to do 3 iterations because codepoints have
|
|
// a maximum length of 4 bytes.
|
|
for _ in 0..3 {
|
|
// The first byte in the string must always be the start of a codepoint.
|
|
if i == 0 {
|
|
break;
|
|
}
|
|
|
|
// SAFETY:
|
|
// `i <= max_len`, since it is never incremented. If this branch is run, then either
|
|
// `src.len(): usize` does not fit into a `u8`, in which case it must be greater
|
|
// than `max_len: u8`, or it does fit into a `u8` but it is greater than `max_len`.
|
|
// Therefore, `src.len() > max_len` must hold. Substitution gives `i < src.len()`,
|
|
// so `i` is a valid index into `src`.
|
|
let byte = unsafe { *src.get_unchecked(usize::from(i)) };
|
|
|
|
// If the byte is not of the form 0b10xxxxxx, then it is the start of a codepoint.
|
|
if byte & 0xc0 != 0x80 {
|
|
break;
|
|
}
|
|
|
|
i -= 1;
|
|
}
|
|
|
|
// `i < src.len()` always holds as discussed above, so the pointer `src.as_ptr()` is
|
|
// valid for reads of `i` bytes. `i` is the index of the start of a codepoint, and
|
|
// codepoints are contiguous, so the `i` bytes being pointed to must be valid UTF-8.
|
|
(src.as_ptr(), i)
|
|
},
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {}
|