diff options
Diffstat (limited to 'syntax/discriminant.rs')
-rw-r--r-- | syntax/discriminant.rs | 89 |
1 files changed, 50 insertions, 39 deletions
diff --git a/syntax/discriminant.rs b/syntax/discriminant.rs index 6a04d881..80f7c0be 100644 --- a/syntax/discriminant.rs +++ b/syntax/discriminant.rs @@ -16,10 +16,16 @@ pub struct DiscriminantSet { #[derive(Copy, Clone, Eq, PartialEq)] pub struct Discriminant { - negative: bool, + sign: Sign, magnitude: u64, } +#[derive(Copy, Clone, Eq, PartialEq)] +enum Sign { + Negative, + Positive, +} + impl DiscriminantSet { pub fn new(repr: Option<Atom>) -> Self { DiscriminantSet { @@ -59,21 +65,23 @@ impl DiscriminantSet { pub fn insert_next(&mut self) -> Result<Discriminant> { let discriminant = match self.previous { None => Discriminant::zero(), - Some(mut discriminant) if discriminant.negative => { - discriminant.magnitude -= 1; - if discriminant.magnitude == 0 { - discriminant.negative = false; + Some(mut discriminant) => match discriminant.sign { + Sign::Negative => { + discriminant.magnitude -= 1; + if discriminant.magnitude == 0 { + discriminant.sign = Sign::Positive; + } + discriminant } - discriminant - } - Some(mut discriminant) => { - if discriminant.magnitude == u64::MAX { - let msg = format!("discriminant overflow on value after {}", u64::MAX); - return Err(Error::new(Span::call_site(), msg)); + Sign::Positive => { + if discriminant.magnitude == u64::MAX { + let msg = format!("discriminant overflow on value after {}", u64::MAX); + return Err(Error::new(Span::call_site(), msg)); + } + discriminant.magnitude += 1; + discriminant } - discriminant.magnitude += 1; - discriminant - } + }, }; insert(self, discriminant) } @@ -109,7 +117,10 @@ fn expr_to_discriminant(expr: &Expr) -> Result<(Discriminant, Option<Atom>)> { Expr::Unary(unary) => { if let UnOp::Neg(_) = unary.op { let (mut discriminant, repr) = expr_to_discriminant(&unary.expr)?; - discriminant.negative ^= true; + discriminant.sign = match discriminant.sign { + Sign::Positive => Sign::Negative, + Sign::Negative => Sign::Positive, + }; return Ok((discriminant, repr)); } } @@ -133,33 +144,33 @@ fn insert(set: &mut DiscriminantSet, discriminant: Discriminant) -> Result<Discr } } } - if set.values.insert(discriminant) { - set.previous = Some(discriminant); - Ok(discriminant) - } else { - let msg = format!("discriminant value `{}` already exists", discriminant); - Err(Error::new(Span::call_site(), msg)) - } + set.values.insert(discriminant); + set.previous = Some(discriminant); + Ok(discriminant) } impl Discriminant { const fn zero() -> Self { Discriminant { - negative: false, + sign: Sign::Positive, magnitude: 0, } } const fn pos(u: u64) -> Self { Discriminant { - negative: false, + sign: Sign::Positive, magnitude: u, } } const fn neg(i: i64) -> Self { Discriminant { - negative: i < 0, + sign: if i < 0 { + Sign::Negative + } else { + Sign::Positive + }, // This is `i.abs() as u64` but without overflow on MIN. Uses the // fact that MIN.wrapping_abs() wraps back to MIN whose binary // representation is 1<<63, and thus the `as u64` conversion @@ -172,7 +183,7 @@ impl Discriminant { impl Display for Discriminant { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { - if self.negative { + if self.sign == Sign::Negative { f.write_str("-")?; } Display::fmt(&self.magnitude, f) @@ -181,7 +192,7 @@ impl Display for Discriminant { impl ToTokens for Discriminant { fn to_tokens(&self, tokens: &mut TokenStream) { - if self.negative { + if self.sign == Sign::Negative { Token![-](Span::call_site()).to_tokens(tokens); } Literal::u64_unsuffixed(self.magnitude).to_tokens(tokens); @@ -192,15 +203,14 @@ impl FromStr for Discriminant { type Err = Error; fn from_str(mut s: &str) -> Result<Self> { - let negative = s.starts_with('-'); - if negative { + let sign = if s.starts_with('-') { s = &s[1..]; - } + Sign::Negative + } else { + Sign::Positive + }; match s.parse::<u64>() { - Ok(magnitude) => Ok(Discriminant { - negative, - magnitude, - }), + Ok(magnitude) => Ok(Discriminant { sign, magnitude }), Err(_) => Err(Error::new( Span::call_site(), "discriminant value outside of supported range", @@ -211,11 +221,12 @@ impl FromStr for Discriminant { impl Ord for Discriminant { fn cmp(&self, other: &Self) -> Ordering { - match (self.negative, other.negative) { - (true, true) => self.magnitude.cmp(&other.magnitude).reverse(), - (true, false) => Ordering::Less, // negative < positive - (false, true) => Ordering::Greater, // positive > negative - (false, false) => self.magnitude.cmp(&other.magnitude), + use self::Sign::{Negative, Positive}; + match (self.sign, other.sign) { + (Negative, Negative) => self.magnitude.cmp(&other.magnitude).reverse(), + (Negative, Positive) => Ordering::Less, // negative < positive + (Positive, Negative) => Ordering::Greater, // positive > negative + (Positive, Positive) => self.magnitude.cmp(&other.magnitude), } } } |