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Shift by KEY_SIZE instead of something larger.

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Currently all Gecko and Servo do the KEY_SHIFT thing, but there's no reason
we need to follow that here.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1371949#c10

MozReview-Commit-ID: CqNi7r9e5s0
This commit is contained in:
Bobby Holley 2017-06-10 09:47:15 -07:00
parent 8085a37178
commit cf982d17b9
1 changed files with 5 additions and 2 deletions
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7
components/selectors/bloom.rs
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@ -7,10 +7,13 @@
use fnv::FnvHasher; use fnv::FnvHasher;
use std::hash::{Hash, Hasher}; use std::hash::{Hash, Hasher};
// The top 12 bits of the 32-bit hash value are not used by the bloom filter.
// Consumers may rely on this to pack hashes more efficiently.
pub const BLOOM_HASH_MASK: u32 = 0x00ffffff;
const KEY_SIZE: usize = 12; const KEY_SIZE: usize = 12;
const ARRAY_SIZE: usize = 1 << KEY_SIZE; const ARRAY_SIZE: usize = 1 << KEY_SIZE;
const KEY_MASK: u32 = (1 << KEY_SIZE) - 1; const KEY_MASK: u32 = (1 << KEY_SIZE) - 1;
const KEY_SHIFT: usize = 16;
/// A counting Bloom filter with 8-bit counters. For now we assume /// A counting Bloom filter with 8-bit counters. For now we assume
/// that having two hash functions is enough, but we may revisit that /// that having two hash functions is enough, but we may revisit that
@ -183,7 +186,7 @@ fn hash1(hash: u32) -> u32 {
#[inline] #[inline]
fn hash2(hash: u32) -> u32 { fn hash2(hash: u32) -> u32 {
(hash >> KEY_SHIFT) & KEY_MASK (hash >> KEY_SIZE) & KEY_MASK
} }
#[test] #[test]