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chore: check seed for CpcSketch and CountMinSketch #85

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chore: check seed for CpcSketch and CountMinSketch #85

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12 changes: 9 additions & 3 deletions datasketches/src/hash/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,15 +39,21 @@ pub(crate) const DEFAULT_UPDATE_SEED: u64 = 9001;

/// Computes and checks the 16-bit seed hash from the given long seed.
///
/// The seed hash may not be zero in order to maintain compatibility with older serialized
/// versions that did not have this concept.
/// The computed seed hash must not be zero in order to maintain compatibility with older
/// serialized versions that did not have this concept.
///
/// # Panics
///
/// Panics if the computed seed hash is zero.
pub(crate) fn compute_seed_hash(seed: u64) -> u16 {
use std::hash::Hasher;

let mut hasher = MurmurHash3X64128::with_seed(0);
hasher.write(&seed.to_le_bytes());
let (h1, _) = hasher.finish128();
(h1 & 0xffff) as u16
let seed_hash = (h1 & 0xffff) as u16;
assert_ne!(seed_hash, 0);
seed_hash
}

/// Reads an u64 from a byte slice in little-endian order.
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