1 use crate::stable_hasher;
3 opaque::{self, EncodeResult, FileEncodeResult},
6 use std::hash::{Hash, Hasher};
7 use std::mem::{self, MaybeUninit};
9 #[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Copy)]
11 pub struct Fingerprint(u64, u64);
14 pub const ZERO: Fingerprint = Fingerprint(0, 0);
17 pub fn new(_0: u64, _1: u64) -> Fingerprint {
22 pub fn from_smaller_hash(hash: u64) -> Fingerprint {
23 Fingerprint(hash, hash)
27 pub fn to_smaller_hash(&self) -> u64 {
28 // Even though both halves of the fingerprint are expected to be good
29 // quality hash values, let's still combine the two values because the
30 // Fingerprints in DefPathHash have the StableCrateId portion which is
31 // the same for all DefPathHashes from the same crate. Combining the
32 // two halfs makes sure we get a good quality hash in such cases too.
33 self.0.wrapping_mul(3).wrapping_add(self.1)
37 pub fn as_value(&self) -> (u64, u64) {
42 pub fn combine(self, other: Fingerprint) -> Fingerprint {
43 // See https://stackoverflow.com/a/27952689 on why this function is
44 // implemented this way.
46 self.0.wrapping_mul(3).wrapping_add(other.0),
47 self.1.wrapping_mul(3).wrapping_add(other.1),
51 // Combines two hashes in an order independent way. Make sure this is what
54 pub fn combine_commutative(self, other: Fingerprint) -> Fingerprint {
55 let a = u128::from(self.1) << 64 | u128::from(self.0);
56 let b = u128::from(other.1) << 64 | u128::from(other.0);
58 let c = a.wrapping_add(b);
60 Fingerprint((c >> 64) as u64, c as u64)
63 pub fn to_hex(&self) -> String {
64 format!("{:x}{:x}", self.0, self.1)
67 pub fn decode_opaque(decoder: &mut opaque::Decoder<'_>) -> Result<Fingerprint, String> {
68 let mut bytes: [MaybeUninit<u8>; 16] = MaybeUninit::uninit_array();
70 decoder.read_raw_bytes(&mut bytes)?;
72 let [l, r]: [u64; 2] = unsafe { mem::transmute(bytes) };
74 Ok(Fingerprint(u64::from_le(l), u64::from_le(r)))
78 impl std::fmt::Display for Fingerprint {
79 fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
80 write!(formatter, "{:x}-{:x}", self.0, self.1)
84 impl Hash for Fingerprint {
86 fn hash<H: Hasher>(&self, state: &mut H) {
87 state.write_fingerprint(self);
91 trait FingerprintHasher {
92 fn write_fingerprint(&mut self, fingerprint: &Fingerprint);
95 impl<H: Hasher> FingerprintHasher for H {
97 default fn write_fingerprint(&mut self, fingerprint: &Fingerprint) {
98 self.write_u64(fingerprint.0);
99 self.write_u64(fingerprint.1);
103 impl FingerprintHasher for crate::unhash::Unhasher {
105 fn write_fingerprint(&mut self, fingerprint: &Fingerprint) {
106 // Even though both halves of the fingerprint are expected to be good
107 // quality hash values, let's still combine the two values because the
108 // Fingerprints in DefPathHash have the StableCrateId portion which is
109 // the same for all DefPathHashes from the same crate. Combining the
110 // two halfs makes sure we get a good quality hash in such cases too.
112 // Since `Unhasher` is used only in the context of HashMaps, it is OK
113 // to combine the two components in an order-independent way (which is
114 // cheaper than the more robust Fingerprint::to_smaller_hash()). For
115 // HashMaps we don't really care if Fingerprint(x,y) and
116 // Fingerprint(y, x) result in the same hash value. Collision
117 // probability will still be much better than with FxHash.
118 self.write_u64(fingerprint.0.wrapping_add(fingerprint.1));
122 impl stable_hasher::StableHasherResult for Fingerprint {
124 fn finish(hasher: stable_hasher::StableHasher) -> Self {
125 let (_0, _1) = hasher.finalize();
130 impl_stable_hash_via_hash!(Fingerprint);
132 impl<E: rustc_serialize::Encoder> Encodable<E> for Fingerprint {
133 fn encode(&self, s: &mut E) -> Result<(), E::Error> {
134 s.encode_fingerprint(self)
138 impl<D: rustc_serialize::Decoder> Decodable<D> for Fingerprint {
139 fn decode(d: &mut D) -> Result<Self, D::Error> {
140 d.decode_fingerprint()
144 pub trait FingerprintEncoder: rustc_serialize::Encoder {
145 fn encode_fingerprint(&mut self, f: &Fingerprint) -> Result<(), Self::Error>;
148 pub trait FingerprintDecoder: rustc_serialize::Decoder {
149 fn decode_fingerprint(&mut self) -> Result<Fingerprint, Self::Error>;
152 impl<E: rustc_serialize::Encoder> FingerprintEncoder for E {
153 default fn encode_fingerprint(&mut self, _: &Fingerprint) -> Result<(), E::Error> {
154 panic!("Cannot encode `Fingerprint` with `{}`", std::any::type_name::<E>());
158 impl FingerprintEncoder for opaque::Encoder {
159 fn encode_fingerprint(&mut self, f: &Fingerprint) -> EncodeResult {
160 let bytes: [u8; 16] = unsafe { mem::transmute([f.0.to_le(), f.1.to_le()]) };
161 self.emit_raw_bytes(&bytes);
166 impl FingerprintEncoder for opaque::FileEncoder {
167 fn encode_fingerprint(&mut self, f: &Fingerprint) -> FileEncodeResult {
168 let bytes: [u8; 16] = unsafe { mem::transmute([f.0.to_le(), f.1.to_le()]) };
169 self.emit_raw_bytes(&bytes)
173 impl<D: rustc_serialize::Decoder> FingerprintDecoder for D {
174 default fn decode_fingerprint(&mut self) -> Result<Fingerprint, D::Error> {
175 panic!("Cannot decode `Fingerprint` with `{}`", std::any::type_name::<D>());
179 impl FingerprintDecoder for opaque::Decoder<'_> {
180 fn decode_fingerprint(&mut self) -> Result<Fingerprint, String> {
181 Fingerprint::decode_opaque(self)
185 // `PackedFingerprint` wraps a `Fingerprint`. Its purpose is to, on certain
186 // architectures, behave like a `Fingerprint` without alignment requirements.
187 // This behavior is only enabled on x86 and x86_64, where the impact of
188 // unaligned accesses is tolerable in small doses.
190 // This may be preferable to use in large collections of structs containing
191 // fingerprints, as it can reduce memory consumption by preventing the padding
192 // that the more strictly-aligned `Fingerprint` can introduce. An application of
193 // this is in the query dependency graph, which contains a large collection of
194 // `DepNode`s. As of this writing, the size of a `DepNode` decreases by ~30%
195 // (from 24 bytes to 17) by using the packed representation here, which
196 // noticeably decreases total memory usage when compiling large crates.
198 // The wrapped `Fingerprint` is private to reduce the chance of a client
199 // invoking undefined behavior by taking a reference to the packed field.
200 #[cfg_attr(any(target_arch = "x86", target_arch = "x86_64"), repr(packed))]
201 #[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Copy, Hash)]
202 pub struct PackedFingerprint(Fingerprint);
204 impl std::fmt::Display for PackedFingerprint {
206 fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
207 // Copy to avoid taking reference to packed field.
213 impl<E: rustc_serialize::Encoder> Encodable<E> for PackedFingerprint {
215 fn encode(&self, s: &mut E) -> Result<(), E::Error> {
216 // Copy to avoid taking reference to packed field.
222 impl<D: rustc_serialize::Decoder> Decodable<D> for PackedFingerprint {
224 fn decode(d: &mut D) -> Result<Self, D::Error> {
225 Fingerprint::decode(d).map(PackedFingerprint)
229 impl From<Fingerprint> for PackedFingerprint {
231 fn from(f: Fingerprint) -> PackedFingerprint {
236 impl From<PackedFingerprint> for Fingerprint {
238 fn from(f: PackedFingerprint) -> Fingerprint {