datasketches 0.2.0

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//   http://www.apache.org/licenses/LICENSE-2.0
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mod murmurhash;
mod xxhash;

pub(crate) use self::murmurhash::MurmurHash3X64128;
#[allow(unused_imports)]
pub(crate) use self::xxhash::XxHash64;

/// The seed 9001 used in the sketch update methods is a prime number that was chosen very early
/// on in experimental testing.
///
/// Choosing a seed is somewhat arbitrary, and the author cannot prove that this particular seed
/// is somehow superior to other seeds. There was some early Internet discussion that a seed of 0
/// did not produce as clean avalanche diagrams as non-zero seeds, but this may have been more
/// related to the MurmurHash2 release, which did have some issues. As far as the author can
/// determine, MurmurHash3 does not have these problems.
///
/// In order to perform set operations on two sketches it is critical that the same hash function
/// and seed are identical for both sketches, otherwise the assumed 1:1 relationship between the
/// original source key value and the hashed bit string would be violated. Once you have developed
/// a history of stored sketches you are stuck with it.
pub(crate) const DEFAULT_UPDATE_SEED: u64 = 9001;

/// Reads an u64 from a byte slice in little-endian order.
///
/// # Panics
///
/// Panics if `bytes.len()` is greater than 8.
fn read_u64_le(bytes: &[u8]) -> u64 {
    let mut buf = [0u8; 8];
    buf[..bytes.len()].copy_from_slice(bytes);
    u64::from_le_bytes(buf)
}