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// Taken from https://github.com/rust-lang/rust/pull/86497
// TODO: Remove when this is in the version of the Rust standard library that delta is building
// against.
#[inline]
const fn is_utf8_char_boundary(b: u8) -> bool {
// This is bit magic equivalent to: b < 128 || b >= 192
(b as i8) >= -0x40
}
#[inline]
pub fn floor_char_boundary(s: &str, index: usize) -> usize {
if index >= s.len() {
s.len()
} else {
let lower_bound = index.saturating_sub(3);
let new_index = s.as_bytes()[lower_bound..=index]
.iter()
.rposition(|b| is_utf8_char_boundary(*b));
// SAFETY: we know that the character boundary will be within four bytes
unsafe { lower_bound + new_index.unwrap_unchecked() }
}
}
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