nordic-dev.net/rust
nordic-dev.net/rust
2
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2025-06-04 19:29:07 +00:00
Code Issues Packages Projects Releases Wiki Activity

Merge pull request #20464 from ranma42/improve-make-hash

Browse Source 
Improve `make_hash` function

Reviewed-by: Gankro, Gankro
This commit is contained in:
bors 2015-01-04 21:36:36 +00:00
commit 05abc65b99
1 changed files with 6 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
src/libstd/collections/hash/table.rs
View File

@ -1,4 +1,4 @@
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at // file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT. // http://rust-lang.org/COPYRIGHT.
// //
@ -139,13 +139,11 @@ impl SafeHash {
/// This function wraps up `hash_keyed` to be the only way outside this /// This function wraps up `hash_keyed` to be the only way outside this
/// module to generate a SafeHash. /// module to generate a SafeHash.
pub fn make_hash<Sized? T: Hash<S>, S, H: Hasher<S>>(hasher: &H, t: &T) -> SafeHash { pub fn make_hash<Sized? T: Hash<S>, S, H: Hasher<S>>(hasher: &H, t: &T) -> SafeHash {
match hasher.hash(t) { // We need to avoid 0u64 in order to prevent collisions with
// This constant is exceedingly likely to hash to the same // EMPTY_HASH. We can maintain our precious uniform distribution
// bucket, but it won't be counted as empty! Just so we can maintain // of initial indexes by unconditionally setting the MSB,
// our precious uniform distribution of initial indexes. // effectively reducing 64-bits hashes to 63 bits.
EMPTY_BUCKET => SafeHash { hash: 0x8000_0000_0000_0000 }, SafeHash { hash: 0x8000_0000_0000_0000 | hasher.hash(t) }
h => SafeHash { hash: h },
}
} }
// `replace` casts a `*u64` to a `*SafeHash`. Since we statically // `replace` casts a `*u64` to a `*SafeHash`. Since we statically