utf8parse/
types.rs

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1//! Types supporting the UTF-8 parser
2
3/// Action to take when receiving a byte
4#[derive(Debug, Copy, Clone)]
5pub enum Action {
6    /// Unexpected byte; sequence is invalid
7    InvalidSequence = 0,
8    /// Received valid 7-bit ASCII byte which can be directly emitted.
9    EmitByte = 1,
10    /// Set the bottom continuation byte
11    SetByte1 = 2,
12    /// Set the 2nd-from-last continuation byte
13    SetByte2 = 3,
14    /// Set the 2nd-from-last byte which is part of a two byte sequence
15    SetByte2Top = 4,
16    /// Set the 3rd-from-last continuation byte
17    SetByte3 = 5,
18    /// Set the 3rd-from-last byte which is part of a three byte sequence
19    SetByte3Top = 6,
20    /// Set the top byte of a four byte sequence.
21    SetByte4 = 7,
22}
23
24/// States the parser can be in.
25///
26/// There is a state for each initial input of the 3 and 4 byte sequences since
27/// the following bytes are subject to different conditions than a tail byte.
28#[allow(non_camel_case_types)]
29#[derive(Debug, Default, Copy, Clone, PartialEq, Eq)]
30pub enum State {
31    /// Ground state; expect anything
32    #[default]
33    Ground = 0,
34    /// 3 tail bytes
35    Tail3 = 1,
36    /// 2 tail bytes
37    Tail2 = 2,
38    /// 1 tail byte
39    Tail1 = 3,
40    /// UTF8-3 starting with E0
41    U3_2_e0 = 4,
42    /// UTF8-3 starting with ED
43    U3_2_ed = 5,
44    /// UTF8-4 starting with F0
45    Utf8_4_3_f0 = 6,
46    /// UTF8-4 starting with F4
47    Utf8_4_3_f4 = 7,
48}
49
50impl State {
51    /// Advance the parser state.
52    ///
53    /// This takes the current state and input byte into consideration, to determine the next state
54    /// and any action that should be taken.
55    #[inline]
56    pub fn advance(self, byte: u8) -> (State, Action) {
57        match self {
58            State::Ground => match byte {
59                0x00..=0x7f => (State::Ground, Action::EmitByte),
60                0xc2..=0xdf => (State::Tail1, Action::SetByte2Top),
61                0xe0 => (State::U3_2_e0, Action::SetByte3Top),
62                0xe1..=0xec => (State::Tail2, Action::SetByte3Top),
63                0xed => (State::U3_2_ed, Action::SetByte3Top),
64                0xee..=0xef => (State::Tail2, Action::SetByte3Top),
65                0xf0 => (State::Utf8_4_3_f0, Action::SetByte4),
66                0xf1..=0xf3 => (State::Tail3, Action::SetByte4),
67                0xf4 => (State::Utf8_4_3_f4, Action::SetByte4),
68                _ => (State::Ground, Action::InvalidSequence),
69            },
70            State::U3_2_e0 => match byte {
71                0xa0..=0xbf => (State::Tail1, Action::SetByte2),
72                _ => (State::Ground, Action::InvalidSequence),
73            },
74            State::U3_2_ed => match byte {
75                0x80..=0x9f => (State::Tail1, Action::SetByte2),
76                _ => (State::Ground, Action::InvalidSequence),
77            },
78            State::Utf8_4_3_f0 => match byte {
79                0x90..=0xbf => (State::Tail2, Action::SetByte3),
80                _ => (State::Ground, Action::InvalidSequence),
81            },
82            State::Utf8_4_3_f4 => match byte {
83                0x80..=0x8f => (State::Tail2, Action::SetByte3),
84                _ => (State::Ground, Action::InvalidSequence),
85            },
86            State::Tail3 => match byte {
87                0x80..=0xbf => (State::Tail2, Action::SetByte3),
88                _ => (State::Ground, Action::InvalidSequence),
89            },
90            State::Tail2 => match byte {
91                0x80..=0xbf => (State::Tail1, Action::SetByte2),
92                _ => (State::Ground, Action::InvalidSequence),
93            },
94            State::Tail1 => match byte {
95                0x80..=0xbf => (State::Ground, Action::SetByte1),
96                _ => (State::Ground, Action::InvalidSequence),
97            },
98        }
99    }
100}
utf8parse/types.rs

utf8parse/
types.rs
