1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101

use crate::stable_hasher;
use std::mem;
use rustc_serialize::opaque::{EncodeResult, Encoder, Decoder};

#[derive(Eq, PartialEq, Ord, PartialOrd, Hash, 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 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 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 stable_hasher::StableHasherResult for Fingerprint {
    #[inline]
    fn finish(hasher: stable_hasher::StableHasher<Self>) -> Self {
        let (_0, _1) = hasher.finalize();
        Fingerprint(_0, _1)
    }
}

impl_stable_hash_via_hash!(Fingerprint);

impl rustc_serialize::UseSpecializedEncodable for Fingerprint { }

impl rustc_serialize::UseSpecializedDecodable for Fingerprint { }

impl rustc_serialize::SpecializedEncoder<Fingerprint> for Encoder {
    fn specialized_encode(&mut self, f: &Fingerprint) -> Result<(), Self::Error> {
        f.encode_opaque(self)
    }
}

impl<'a> rustc_serialize::SpecializedDecoder<Fingerprint> for Decoder<'a> {
    fn specialized_decode(&mut self) -> Result<Fingerprint, Self::Error> {
        Fingerprint::decode_opaque(self)
    }
}