From 474cc91440ecb89a4d7ea81b1786fddbf2b70641 Mon Sep 17 00:00:00 2001
From: Michael Woerister <michaelwoerister@posteo.net>
Date: Wed, 17 May 2017 16:41:07 +0200
Subject: [PATCH] Use in-memory representation for Fingerprint that is more
 amenable to hashing.

---
 src/librustc/ich/fingerprint.rs | 72 ++++++++++++---------------------
 1 file changed, 26 insertions(+), 46 deletions(-)

diff --git a/src/librustc/ich/fingerprint.rs b/src/librustc/ich/fingerprint.rs
index ccdbab88b8b..a947f6aeff7 100644
--- a/src/librustc/ich/fingerprint.rs
+++ b/src/librustc/ich/fingerprint.rs
@@ -10,95 +10,75 @@
 
 use rustc_serialize::{Encodable, Decodable, Encoder, Decoder};
 use rustc_data_structures::stable_hasher;
-use rustc_data_structures::ToHex;
-
-const FINGERPRINT_LENGTH: usize = 16;
+use std::mem;
+use std::slice;
 
 #[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Clone, Copy)]
-pub struct Fingerprint(pub [u8; FINGERPRINT_LENGTH]);
+pub struct Fingerprint(u64, u64);
 
 impl Fingerprint {
     #[inline]
     pub fn zero() -> Fingerprint {
-        Fingerprint([0; FINGERPRINT_LENGTH])
+        Fingerprint(0, 0)
     }
 
+    #[inline]
     pub fn from_smaller_hash(hash: u64) -> Fingerprint {
-        let mut result = Fingerprint::zero();
-        result.0[0] = (hash >>  0) as u8;
-        result.0[1] = (hash >>  8) as u8;
-        result.0[2] = (hash >> 16) as u8;
-        result.0[3] = (hash >> 24) as u8;
-        result.0[4] = (hash >> 32) as u8;
-        result.0[5] = (hash >> 40) as u8;
-        result.0[6] = (hash >> 48) as u8;
-        result.0[7] = (hash >> 56) as u8;
-        result
+        Fingerprint(hash, hash)
     }
 
+    #[inline]
     pub fn to_smaller_hash(&self) -> u64 {
-        ((self.0[0] as u64) <<  0) |
-        ((self.0[1] as u64) <<  8) |
-        ((self.0[2] as u64) << 16) |
-        ((self.0[3] as u64) << 24) |
-        ((self.0[4] as u64) << 32) |
-        ((self.0[5] as u64) << 40) |
-        ((self.0[6] as u64) << 48) |
-        ((self.0[7] as u64) << 56)
+        self.0
     }
 
     pub fn to_hex(&self) -> String {
-        self.0.to_hex()
+        format!("{:x}{:x}", self.0, self.1)
     }
 }
 
 impl Encodable for Fingerprint {
     #[inline]
     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
-        for &byte in &self.0 {
-            s.emit_u8(byte)?;
-        }
-        Ok(())
+        s.emit_u64(self.0.to_le())?;
+        s.emit_u64(self.1.to_le())
     }
 }
 
 impl Decodable for Fingerprint {
     #[inline]
     fn decode<D: Decoder>(d: &mut D) -> Result<Fingerprint, D::Error> {
-        let mut result = Fingerprint([0u8; FINGERPRINT_LENGTH]);
-        for byte in &mut result.0 {
-            *byte = d.read_u8()?;
-        }
-        Ok(result)
+        let _0 = u64::from_le(d.read_u64()?);
+        let _1 = u64::from_le(d.read_u64()?);
+        Ok(Fingerprint(_0, _1))
     }
 }
 
 impl ::std::fmt::Display for Fingerprint {
     fn fmt(&self, formatter: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
-        for i in 0 .. self.0.len() {
-            if i > 0 {
-                write!(formatter, "::")?;
-            }
-
-            write!(formatter, "{}", self.0[i])?;
-        }
-        Ok(())
+        write!(formatter, "{:x}-{:x}", self.0, self.1)
     }
 }
 
-
 impl stable_hasher::StableHasherResult for Fingerprint {
     fn finish(mut hasher: stable_hasher::StableHasher<Self>) -> Self {
-        let mut fingerprint = Fingerprint::zero();
-        fingerprint.0.copy_from_slice(hasher.finalize());
-        fingerprint
+        let hash_bytes: &[u8] = hasher.finalize();
+
+        assert!(hash_bytes.len() >= mem::size_of::<u64>() * 2);
+        let hash_bytes: &[u64] = unsafe {
+            slice::from_raw_parts(hash_bytes.as_ptr() as *const u64, 2)
+        };
+
+        // The bytes returned bytes the Blake2B hasher are always little-endian.
+        Fingerprint(u64::from_le(hash_bytes[0]), u64::from_le(hash_bytes[1]))
     }
 }
 
 impl<CTX> stable_hasher::HashStable<CTX> for Fingerprint {
+    #[inline]
     fn hash_stable<W: stable_hasher::StableHasherResult>(&self,
                                           _: &mut CTX,
                                           hasher: &mut stable_hasher::StableHasher<W>) {
-        ::std::hash::Hash::hash(&self.0, hasher);
+        ::std::hash::Hash::hash(self, hasher);
     }
 }
-- 
2.44.0