datasketches 0.3.0-rc.2

A software library of stochastic streaming algorithms (a.k.a. sketches)
Documentation 
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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

//! Theta sketch implementation for cardinality estimation.
//!
//! Theta sketch is a generalization of the Kth Minimum Value (KMV) sketch that uses
//! a hash table to store retained entries and a theta parameter (sampling threshold)
//! to control memory usage. When the hash table reaches capacity, theta is reduced
//! to maintain the nominal size k.
//!
//! # Overview
//!
//! Theta sketches provide approximate distinct count (cardinality) estimation with
//! configurable accuracy and memory usage. The implementation supports:
//!
//! * **ThetaSketch**: Mutable sketch for building from input data
//! * **CompactThetaSketch**: Immutable sketch with compact memory layout
//!
//! # Usage
//!
//! ```
//! # use datasketches::theta::ThetaSketch;
//! let mut sketch = ThetaSketch::builder().build();
//! sketch.update("apple");
//! assert!(sketch.estimate() >= 1.0);
//! ```

mod bit_pack;
mod hash_table;
mod intersection;
mod serialization;
mod sketch;

pub use self::intersection::ThetaIntersection;
pub use self::sketch::CompactThetaSketch;
pub use self::sketch::ThetaSketch;
pub use self::sketch::ThetaSketchBuilder;
pub use self::sketch::ThetaSketchView;

/// Maximum theta value (signed max for compatibility with Java)
const MAX_THETA: u64 = i64::MAX as u64;
/// Minimum log2 of K
const MIN_LG_K: u8 = 5;
/// Maximum log2 of K
const MAX_LG_K: u8 = 26;
/// Default log2 of K
const DEFAULT_LG_K: u8 = 12;
/// Resize threshold (0.5 = 50% load factor)
const HASH_TABLE_RESIZE_THRESHOLD: f64 = 0.5;
/// Rebuild threshold (15/16 = 93.75% load factor)
const HASH_TABLE_REBUILD_THRESHOLD: f64 = 15.0 / 16.0;