Struct HyperLogLog 

pub struct HyperLogLog { /* private fields */ }

HyperLogLog++ for cardinality estimation with sparse/dense hybrid

Standard error: 1.04 / sqrt(m) where m = 2^precision

• precision=10: m=1024, error ≈ 3.25%
• precision=12: m=4096, error ≈ 1.63%
• precision=14: m=16384, error ≈ 0.81%

Gap #2 Implementation: Starts in sparse mode for memory efficiency, automatically converts to dense mode when cardinality exceeds threshold.

Implementations

impl HyperLogLog

pub fn new(precision: u8) -> Self

Create with specified precision (starts in sparse mode)

Arguments

• precision - Number of bits for register selection (4-18)
  • p=10: 1KB memory (dense), ~3.25% error
  • p=12: 4KB memory (dense), ~1.63% error
  • p=14: 16KB memory (dense), ~0.81% error

Gap #2: Starts in sparse mode for memory efficiency

pub fn new_dense(precision: u8) -> Self

Create with specified precision, forcing dense mode from start Use this when you know cardinality will be high

pub fn default_precision() -> Self

Create with default precision (14 = 0.81% error)

pub fn is_sparse(&self) -> bool

Check if currently in sparse mode

pub fn add<T: Hash>(&mut self, item: &T)

Add an item to the sketch

pub fn add_hash(&mut self, hash: u64)

Add a pre-hashed value (for when you already have the hash)

pub fn cardinality(&self) -> u64

Estimate cardinality with HLL++ bias correction

Gap #6 Fix: Implements proper HLL++ bias correction for small cardinalities using empirical bias estimates from the HyperLogLog++ paper.

pub fn merge(&mut self, other: &HyperLogLog)

Merge another HyperLogLog into this one

Critical for time bucket rollups Gap #2: Handles all combinations of sparse/dense merges efficiently

pub fn is_empty(&self) -> bool

Check if empty

pub fn clear(&mut self)

Clear all data (resets to sparse mode)

pub fn memory_usage(&self) -> usize

Get memory usage in bytes

pub fn precision(&self) -> u8

Get precision

pub fn standard_error(&self) -> f64

Get standard error percentage

pub fn non_zero_count(&self) -> usize

Get number of non-zero registers (useful for debugging sparse mode)

Trait Implementations

impl Clone for HyperLogLog

fn clone(&self) -> HyperLogLog

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for HyperLogLog

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for HyperLogLog

fn default() -> Self

Returns the “default value” for a type.