netspeed_cli/formatter/
stability.rs

1//! Speed stability analysis and latency percentiles.
2
3#![allow(
4    clippy::cast_precision_loss,
5    clippy::cast_possible_truncation,
6    clippy::cast_sign_loss
7)]
8
9use owo_colors::OwoColorize;
10
11/// Compute coefficient of variation (CV) as a percentage.
12#[must_use]
13pub fn compute_cv(speeds: &[f64]) -> f64 {
14    if speeds.is_empty() {
15        return 0.0;
16    }
17    let n = speeds.len() as f64;
18    let mean = speeds.iter().sum::<f64>() / n;
19    if mean <= 0.0 {
20        return 0.0;
21    }
22    let variance = speeds.iter().map(|s| (s - mean).powi(2)).sum::<f64>() / n;
23    let stddev = variance.sqrt();
24    (stddev / mean) * 100.0
25}
26
27pub fn format_stability_line(cv: f64, nc: bool) -> String {
28    let (color, label) = if cv < 5.0 {
29        ("green", "rock-solid")
30    } else if cv < 10.0 {
31        ("bright_green", "very stable")
32    } else if cv < 20.0 {
33        ("yellow", "moderate")
34    } else if cv < 35.0 {
35        ("bright_yellow", "variable")
36    } else {
37        ("red", "unstable")
38    };
39    let text = format!("±{cv:.0}% {label}");
40    if nc {
41        text
42    } else {
43        match color {
44            "green" => text.green().to_string(),
45            "bright_green" => text.bright_green().to_string(),
46            "yellow" => text.yellow().to_string(),
47            "bright_yellow" => text.bright_yellow().to_string(),
48            "red" => text.red().bold().to_string(),
49            _ => text.to_string(),
50        }
51    }
52}
53
54pub fn compute_percentiles(samples: &[f64]) -> Option<(f64, f64, f64)> {
55    let n = samples.len();
56    if n < 3 {
57        return None;
58    }
59    let mut data = samples.to_vec();
60    let p50_idx = n * 50 / 100;
61    let p95_idx = (n * 95 / 100).min(n - 1);
62    let p99_idx = (n * 99 / 100).min(n - 1);
63
64    // Partition at p99: elements before are <= p99, elements after are >= p99
65    data.select_nth_unstable_by(p99_idx, |a, b| {
66        a.partial_cmp(b).unwrap_or(std::cmp::Ordering::Equal)
67    });
68    let p99 = data[p99_idx];
69
70    // Partition the left slice at p95
71    data.select_nth_unstable_by(p95_idx, |a, b| {
72        a.partial_cmp(b).unwrap_or(std::cmp::Ordering::Equal)
73    });
74    let p95 = data[p95_idx];
75
76    // Partition the left slice at p50
77    data.select_nth_unstable_by(p50_idx, |a, b| {
78        a.partial_cmp(b).unwrap_or(std::cmp::Ordering::Equal)
79    });
80    let p50 = data[p50_idx];
81
82    Some((p50, p95, p99))
83}
84
85#[cfg(test)]
86mod tests {
87    use super::*;
88
89    #[test]
90    fn test_compute_cv_constant() {
91        let speeds = vec![100.0, 100.0, 100.0];
92        assert_eq!(compute_cv(&speeds), 0.0);
93    }
94
95    #[test]
96    fn test_compute_cv_empty() {
97        assert_eq!(compute_cv(&[]), 0.0);
98    }
99
100    #[test]
101    fn test_compute_percentiles_basic() {
102        let samples: Vec<f64> = (1..=100).map(|x| x as f64).collect();
103        let result = compute_percentiles(&samples);
104        assert!(result.is_some());
105        let (p50, p95, p99) = result.unwrap();
106        // With 100 elements (indices 0..99), n*50/100 = 50 → index 50 → value 51.0
107        assert!((p50 - 51.0).abs() < 1.0);
108        assert!((p95 - 96.0).abs() < 1.0);
109        assert!((p99 - 100.0).abs() < 1.0);
110    }
111
112    #[test]
113    fn test_compute_percentiles_too_few() {
114        assert!(compute_percentiles(&[1.0, 2.0]).is_none());
115    }
116}
netspeed_cli/formatter/stability.rs

netspeed_cli/formatter/
stability.rs
