rust/compiler/rustc_data_structures/src/fingerprint.rs

use crate::stable_hasher;
use rustc_serialize::{
    opaque::{self, EncodeResult},
    Decodable, Encodable,
};
use std::hash::{Hash, Hasher};
use std::mem;

#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Copy)]
pub struct Fingerprint(u64, u64);

impl Fingerprint {
    pub const ZERO: Fingerprint = Fingerprint(0, 0);

    #[inline]
    pub fn from_smaller_hash(hash: u64) -> Fingerprint {
        Fingerprint(hash, hash)
    }

    #[inline]
    pub fn to_smaller_hash(&self) -> u64 {
        self.0
    }

    #[inline]
    pub fn as_value(&self) -> (u64, u64) {
        (self.0, self.1)
    }

    #[inline]
    pub fn combine(self, other: Fingerprint) -> Fingerprint {
        // See https://stackoverflow.com/a/27952689 on why this function is
        // implemented this way.
        Fingerprint(
            self.0.wrapping_mul(3).wrapping_add(other.0),
            self.1.wrapping_mul(3).wrapping_add(other.1),
        )
    }

    // Combines two hashes in an order independent way. Make sure this is what
    // you want.
    #[inline]
    pub fn combine_commutative(self, other: Fingerprint) -> Fingerprint {
        let a = u128::from(self.1) << 64 | u128::from(self.0);
        let b = u128::from(other.1) << 64 | u128::from(other.0);

        let c = a.wrapping_add(b);

        Fingerprint((c >> 64) as u64, c as u64)
    }

    pub fn to_hex(&self) -> String {
        format!("{:x}{:x}", self.0, self.1)
    }

    pub fn encode_opaque(&self, encoder: &mut opaque::Encoder) -> EncodeResult {
        let bytes: [u8; 16] = unsafe { mem::transmute([self.0.to_le(), self.1.to_le()]) };

        encoder.emit_raw_bytes(&bytes);
        Ok(())
    }

    pub fn decode_opaque(decoder: &mut opaque::Decoder<'_>) -> Result<Fingerprint, String> {
        let mut bytes = [0; 16];

        decoder.read_raw_bytes(&mut bytes)?;

        let [l, r]: [u64; 2] = unsafe { mem::transmute(bytes) };

        Ok(Fingerprint(u64::from_le(l), u64::from_le(r)))
    }
}

impl std::fmt::Display for Fingerprint {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(formatter, "{:x}-{:x}", self.0, self.1)
    }
}

impl Hash for Fingerprint {
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        state.write_fingerprint(self);
    }
}

trait FingerprintHasher {
    fn write_fingerprint(&mut self, fingerprint: &Fingerprint);
}

impl<H: Hasher> FingerprintHasher for H {
    #[inline]
    default fn write_fingerprint(&mut self, fingerprint: &Fingerprint) {
        self.write_u64(fingerprint.0);
        self.write_u64(fingerprint.1);
    }
}

impl FingerprintHasher for crate::unhash::Unhasher {
    #[inline]
    fn write_fingerprint(&mut self, fingerprint: &Fingerprint) {
        // `Unhasher` only wants a single `u64`
        self.write_u64(fingerprint.0);
    }
}

impl stable_hasher::StableHasherResult for Fingerprint {
    #[inline]
    fn finish(hasher: stable_hasher::StableHasher) -> Self {
        let (_0, _1) = hasher.finalize();
        Fingerprint(_0, _1)
    }
}

impl_stable_hash_via_hash!(Fingerprint);

impl<E: rustc_serialize::Encoder> Encodable<E> for Fingerprint {
    fn encode(&self, s: &mut E) -> Result<(), E::Error> {
        s.encode_fingerprint(self)
    }
}

impl<D: rustc_serialize::Decoder> Decodable<D> for Fingerprint {
    fn decode(d: &mut D) -> Result<Self, D::Error> {
        d.decode_fingerprint()
    }
}

pub trait FingerprintEncoder: rustc_serialize::Encoder {
    fn encode_fingerprint(&mut self, f: &Fingerprint) -> Result<(), Self::Error>;
}

pub trait FingerprintDecoder: rustc_serialize::Decoder {
    fn decode_fingerprint(&mut self) -> Result<Fingerprint, Self::Error>;
}

impl<E: rustc_serialize::Encoder> FingerprintEncoder for E {
    default fn encode_fingerprint(&mut self, _: &Fingerprint) -> Result<(), E::Error> {
        panic!("Cannot encode `Fingerprint` with `{}`", std::any::type_name::<E>());
    }
}

impl FingerprintEncoder for opaque::Encoder {
    fn encode_fingerprint(&mut self, f: &Fingerprint) -> EncodeResult {
        f.encode_opaque(self)
    }
}

impl<D: rustc_serialize::Decoder> FingerprintDecoder for D {
    default fn decode_fingerprint(&mut self) -> Result<Fingerprint, D::Error> {
        panic!("Cannot decode `Fingerprint` with `{}`", std::any::type_name::<D>());
    }
}
impl FingerprintDecoder for opaque::Decoder<'_> {
    fn decode_fingerprint(&mut self) -> Result<Fingerprint, String> {
        Fingerprint::decode_opaque(self)
    }
}