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May 6, 2024 19:10
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| impl<V: Value> core::str::FromStr for NonNormalizingDec<V> { | |
| type Err = &'static str; | |
| #[inline(never)] | |
| #[rustfmt::skip] | |
| fn from_str(s: &str) -> Result<Self, Self::Err> { | |
| /// Converts an ASCII decimal digit to an int. | |
| /// | |
| /// In release builds, no range checks are performed and passing a | |
| /// non-digit character will result is undefined (yet safe) behavior. | |
| fn digit2num(x: char) -> i8 { | |
| debug_assert!(x >= '0' && x <= '9'); | |
| let out = x as i8 - '0' as i8; | |
| debug_assert!(out >= 0 && out <= 9); | |
| out | |
| } | |
| fn push<V: Value>(nn: &mut NonNormalizingDec<V>, digit: char) { | |
| let digit = V::from_i8(digit2num(digit)).unwrap(); | |
| nn.v = nn.v.clone() * V::ten() + digit; | |
| } | |
| fn push_fract<V: Value>(nn: &mut NonNormalizingDec<V>, digit: char) { | |
| push(nn, digit); | |
| nn.s += 1; | |
| } | |
| enum ReadStatus { | |
| Enough, | |
| NeedMore, | |
| } | |
| enum PosNeg { | |
| Pos, | |
| Neg, | |
| } | |
| enum ParserState { | |
| Sign, | |
| Int(ReadStatus), | |
| Frac, | |
| ExpSign, | |
| Exp(PosNeg, Scale), | |
| } | |
| use ParserState::*; | |
| use PosNeg::*; | |
| use ReadStatus::*; | |
| let mut iter = s.chars(); | |
| let mut state = ParserState::Sign; | |
| let mut sign = V::one(); | |
| let mut out = Self::zero(); | |
| loop { match (&mut state, iter.next()) { | |
| (Sign , Some('+' )) => state = Int(NeedMore), | |
| (Sign , Some('-' )) => { sign = -V::one(); state = Int(NeedMore) } | |
| (Sign , Some(x @ '0'..='9')) => { push(&mut out, x); state = Int(Enough) } | |
| (Sign , Some(_ )) => return Err("unexpected char (sign)"), | |
| (Sign , None ) => return Err("empty string"), | |
| (Int(status ), Some(x @ '0'..='9')) => { push(&mut out, x); *status = Enough; } | |
| (Int(Enough ), Some('e' | 'E') ) => state = ExpSign, | |
| (Int(Enough ), Some('.' )) => state = Frac, | |
| (Int(Enough ), None ) => break, | |
| (Int(NeedMore), _ ) => return Err("expected digits"), | |
| (Int(_ ), Some(_ )) => return Err("unexpected char (int)"), | |
| (Frac , Some(x @ '0'..='9')) => push_fract(&mut out, x), | |
| (Frac , Some('e' | 'E' )) => state = ExpSign, | |
| (Frac , Some(_ )) => return Err("unexpected char (frac)"), | |
| (Frac , None ) => break, | |
| (ExpSign , Some('+' )) => state = Exp(Pos, 0), | |
| (ExpSign , Some('-' )) => state = Exp(Neg, 0), | |
| (ExpSign , Some(x @ '0'..='9')) => state = Exp(Pos, digit2num(x) as Scale), | |
| (ExpSign , Some(_ )) => return Err("unexpected char (exp sign)"), | |
| (ExpSign , None ) => return Err("unexpected end (exp sign)"), | |
| (Exp(_ , exp), Some(x @ '0'..='9')) => *exp = *exp * 10 + digit2num(x) as Scale, | |
| (Exp(_ , _ ), Some(_ )) => return Err("unexpected char (exp)"), | |
| (Exp(Pos, exp), None ) => { out *= Self::pow10(*exp); break } | |
| (Exp(Neg, exp), None ) => { out *= Self::pow10(-*exp); break } | |
| }} | |
| out.v *= sign; | |
| Ok(out) | |
| } | |
| } |
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