cb_digest/
config.rs

1#[cfg(feature = "use_serde")]
2use serde::{Deserialize, Serialize};
3
4#[cfg(feature = "use_rkyv")]
5use rkyv::{Deserialize, Serialize, Archive};
6
7const DEFAULT_MAX_BINS: u32 = 2048;
8const DEFAULT_ALPHA: f64 = 0.01;
9const DEFAULT_MIN_VALUE: f64 = 1.0e-9;
10
11/// The configuration struct for constructing a `DDSketch`
12#[derive(Copy, Clone, Debug, PartialEq)]
13#[cfg_attr(feature = "use_serde", derive(Serialize, Deserialize))]
14#[cfg_attr(feature = "use_rkyv", derive(Serialize, Deserialize, Archive))]
15pub struct Config {
16    pub max_num_bins: u32,
17    pub gamma: f64,
18    gamma_ln: f64,
19    min_value: f64,
20    pub offset: i32,
21}
22
23fn log_gamma(value: f64, gamma_ln: f64) -> f64 {
24    value.ln() / gamma_ln
25}
26
27impl Config {
28    /// Construct a new `Config` struct with specific parameters. If you are unsure of how to
29    /// configure this, the `defaults` method constructs a `Config` with built-in defaults.
30    ///
31    /// `max_num_bins` is the max number of bins the DDSketch will grow to, in steps of 128 bins.
32    pub fn new(alpha: f64, max_num_bins: u32, min_value: f64) -> Self {
33        let gamma_ln = (2.0 * alpha) / (1.0 - alpha);
34        let gamma_ln = gamma_ln.ln_1p();
35
36        Config {
37            max_num_bins,
38            gamma: 1.0 + (2.0 * alpha) / (1.0 - alpha),
39            gamma_ln,
40            min_value,
41            offset: 1 - (log_gamma(min_value, gamma_ln) as i32),
42        }
43    }
44
45    /// Return a `Config` using built-in default settings
46    pub fn defaults() -> Self {
47        Self::new(DEFAULT_ALPHA, DEFAULT_MAX_BINS, DEFAULT_MIN_VALUE)
48    }
49
50    pub fn key(&self, v: f64) -> i32 {
51        self.log_gamma(v).ceil() as i32
52    }
53
54    pub fn value(&self, key: i32) -> f64 {
55        self.pow_gamma(key) * (2.0 / (1.0 + self.gamma))
56    }
57
58    pub fn log_gamma(&self, value: f64) -> f64 {
59        log_gamma(value, self.gamma_ln)
60    }
61
62    pub fn pow_gamma(&self, key: i32) -> f64 {
63        ((key as f64) * self.gamma_ln).exp()
64    }
65
66    pub fn min_possible(&self) -> f64 {
67        self.min_value
68    }
69}
70
71impl Default for Config {
72    fn default() -> Self {
73        Self::new(DEFAULT_ALPHA, DEFAULT_MAX_BINS, DEFAULT_MIN_VALUE)
74    }
75}
cb_digest/config.rs

cb_digest/
config.rs
