decdn-reputation 0.0.2

Local per-peer reputation scoring for deCDN nodes (ADR 008): EWMA over observed outcomes, with no gossip aggregation
Documentation 
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//! Shared interaction-score arithmetic (ADR 008 §Local Score Calculation).
//!
//! The local scorer ([`crate::local`]) scores a single interaction as
//! `0.4 * speed + 0.4 * correctness + 0.2 * reachability`. This module is the
//! one place that arithmetic lives.

use std::time::Duration;

/// The three component weights for an interaction score. Each is in `[0, 1]`
/// and the three sum to `1.0` (validated by the owning config).
#[derive(Debug, Clone, Copy)]
pub(crate) struct InteractionWeights {
    pub speed: f64,
    pub correctness: f64,
    pub reachability: f64,
}

/// Log-normalized delivery-speed score in `[0, 1]` (ADR 008 §Local Score
/// Calculation), computed from a byte count and the time it took to transfer
/// them. `reference_bps` is the throughput that scores ~1.0. Returns `0.0`
/// for non-positive or non-finite inputs (ADR 008 §Local Score Calculation
/// normalization).
// u64→f64 loses precision above 2^53 (~9 PB) — far above any plausible single
// transfer; the result is clamped to [0, 1] so any drift rounds within the
// saturated range and cannot escape the score envelope.
#[allow(clippy::cast_precision_loss)]
pub(crate) fn speed_score_from_transfer(bytes: u64, elapsed: Duration, reference_bps: u64) -> f64 {
    let secs = elapsed.as_secs_f64();
    if !secs.is_finite() || secs <= 0.0 || reference_bps == 0 {
        return 0.0;
    }
    speed_score_from_bps(bytes as f64 / secs, reference_bps)
}

/// Log-normalized delivery-speed score in `[0, 1]` (ADR 008 §Local Score
/// Calculation). `reference_bps` is the throughput that scores ~1.0. The log
/// shape keeps throughput from saturating — a materially faster node scores
/// strictly higher. Returns
/// `0.0` for non-positive / non-finite input or a zero reference.
#[allow(clippy::cast_precision_loss)]
pub(crate) fn speed_score_from_bps(bytes_per_sec: f64, reference_bps: u64) -> f64 {
    if !bytes_per_sec.is_finite() || bytes_per_sec <= 0.0 || reference_bps == 0 {
        return 0.0;
    }
    // `ln_1p(x)` computes `ln(1 + x)` without the catastrophic cancellation a
    // literal `(1.0 + x).ln()` suffers for very small `x` — so a near-zero-rate
    // transfer is scored accurately rather than swamped by float error.
    let denom = (reference_bps as f64).ln_1p();
    (bytes_per_sec.ln_1p() / denom).clamp(0.0, 1.0)
}

/// `w.speed * speed + w.correctness * correctness + w.reachability *
/// reachability` for component scores each already in `[0, 1]`.
pub(crate) fn interaction_score(
    w: InteractionWeights,
    speed: f64,
    correctness: f64,
    reachability: f64,
) -> f64 {
    w.speed * speed + w.correctness * correctness + w.reachability * reachability
}

#[cfg(test)]
mod tests;