jiff/shared/util/
utf8.rs

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1/// Decodes the next UTF-8 encoded codepoint from the given byte slice.
2///
3/// If no valid encoding of a codepoint exists at the beginning of the
4/// given byte slice, then the first byte is returned instead.
5///
6/// This returns `None` if and only if `bytes` is empty.
7///
8/// This never panics.
9///
10/// *WARNING*: This is not designed for performance. If you're looking for
11/// a fast UTF-8 decoder, this is not it. If you feel like you need one in
12/// this crate, then please file an issue and discuss your use case.
13pub(crate) fn decode(bytes: &[u8]) -> Option<Result<char, u8>> {
14    /// Given a UTF-8 leading byte, this returns the total number of code
15    /// units in the following encoded codepoint.
16    ///
17    /// If the given byte is not a valid UTF-8 leading byte, then this
18    /// returns `None`.
19    fn utf8_len(byte: u8) -> Option<usize> {
20        if byte <= 0x7F {
21            return Some(1);
22        } else if byte & 0b1100_0000 == 0b1000_0000 {
23            return None;
24        } else if byte <= 0b1101_1111 {
25            Some(2)
26        } else if byte <= 0b1110_1111 {
27            Some(3)
28        } else if byte <= 0b1111_0111 {
29            Some(4)
30        } else {
31            None
32        }
33    }
34
35    if bytes.is_empty() {
36        return None;
37    }
38    let len = match utf8_len(bytes[0]) {
39        None => return Some(Err(bytes[0])),
40        Some(len) if len > bytes.len() => return Some(Err(bytes[0])),
41        Some(1) => return Some(Ok(char::from(bytes[0]))),
42        Some(len) => len,
43    };
44    match core::str::from_utf8(&bytes[..len]) {
45        Ok(s) => Some(Ok(s.chars().next().unwrap())),
46        Err(_) => Some(Err(bytes[0])),
47    }
48}
jiff/shared/util/utf8.rs

jiff/shared/util/
utf8.rs
