scolapasta_int_parse/
parser.rs

1use alloc::string::String;
2
3use crate::error::ArgumentError;
4use crate::subject::IntegerString;
5
6#[must_use]
7#[derive(Default, Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
8pub enum Sign {
9    #[default]
10    Positive,
11    Negative,
12}
13
14#[must_use]
15#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
16pub enum State<'a> {
17    Initial(IntegerString<'a>),
18    Sign(IntegerString<'a>, Sign),
19    Accumulate(IntegerString<'a>, String),
20}
21
22impl<'a> State<'a> {
23    #[inline]
24    pub fn new(subject: IntegerString<'a>) -> Self {
25        Self::Initial(subject)
26    }
27
28    pub fn set_sign(self, sign: Sign) -> Result<Self, ArgumentError<'a>> {
29        match self {
30            Self::Sign(subject, _) | Self::Accumulate(subject, _) => Err(subject.into()),
31            Self::Initial(subject) => Ok(Self::Sign(subject, sign)),
32        }
33    }
34
35    pub fn collect_digit(self, digit: u8) -> Self {
36        // For `i64::MIN` and `i64::MAX` in base 10:
37        //
38        // ```
39        // [3.1.2] > 2 ** 64 - 1
40        // => 18446744073709551615
41        // [3.1.2] > (2 ** 64 - 1).to_s.length
42        // => 20
43        // [3.1.2] > -(2 ** 64)
44        // => -18446744073709551616
45        // [3.1.2] > (-(2 ** 64 - 1)).to_s.length
46        // => 21
47        // ```
48        //
49        // In bases below 10, the string representation for large numbers will
50        // be longer, but pre-allocating for these uncommon cases seems wasteful.
51        // The `String` will reallocate if it needs to in these pathological cases.
52        const PRE_ALLOCATED_DIGIT_CAPACITY: usize = 21;
53
54        match self {
55            Self::Initial(arg) => {
56                let mut digits = String::with_capacity(PRE_ALLOCATED_DIGIT_CAPACITY);
57                digits.push(char::from(digit));
58                Self::Accumulate(arg, digits)
59            }
60            Self::Sign(arg, sign) => {
61                let mut digits = String::with_capacity(PRE_ALLOCATED_DIGIT_CAPACITY);
62                if let Sign::Negative = sign {
63                    digits.push('-');
64                }
65                digits.push(char::from(digit));
66                Self::Accumulate(arg, digits)
67            }
68            Self::Accumulate(arg, mut digits) => {
69                digits.push(char::from(digit));
70                Self::Accumulate(arg, digits)
71            }
72        }
73    }
74
75    pub fn into_numeric_string(self) -> Result<String, ArgumentError<'a>> {
76        match self {
77            Self::Accumulate(_, digits) => Ok(digits),
78            Self::Initial(subject) | Self::Sign(subject, _) => Err(subject.into()),
79        }
80    }
81}
scolapasta_int_parse/parser.rs

scolapasta_int_parse/
parser.rs
