counterpoint-engine-rs

Species counterpoint rule checker — interval classification, first-species rules (parallel 5ths/octaves, voice crossing, leap limits), and consonance scoring.

What This Gives You

• Interval classification — Consonance, dissonance, perfect/imperfect intervals
• First species rules — Dissonance detection, parallel 5ths/octaves, voice crossing
• Leap checking — Configurable maximum leap size
• Scoring — Consonance ratio minus violation penalties

Quick Start

use counterpoint_engine::{VoicePair, CounterpointChecker};

let pair = VoicePair::new(
    vec![60, 62, 64, 65, 67],  // C D E F G (cantus firmus)
    vec![64, 65, 67, 69, 71],  // E F G A B (counterpoint)
);

let checker = CounterpointChecker::default();
let result = checker.check(&pair);

if result.is_valid() {
    println!("Valid counterpoint! Score: {:.2}", result.score);
} else {
    for v in &result.violations {
        println!("Violation: {:?}", v);
    }
}

API Reference

VoicePair

VoicePair::new(cantus_firmus, counterpoint)  // Two pitch sequences (MIDI note numbers)

CounterpointChecker

CounterpointChecker::default()               // Standard first-species rules
checker.check(&pair) -> CheckResult          // Evaluate all rules

CheckResult

Field	Description
is_valid()	Passed all rules
score	Consonance ratio minus penalties
violations	Vec of specific rule violations

How It Fits

• counterpoint-engine-c — C99 port of this library
• constraint-instrument — Counterpoint rules as constraint surfaces for interactive music
• flux-algebra-rs — Harmonic ring and tuning systems for interval computation

Testing

9 tests covering interval classification, consonance detection, parallel motion rules, voice crossing, and scoring.

cargo test

Installation

[dependencies]
counterpoint-engine = { git = "https://github.com/SuperInstance/counterpoint-engine-rs" }

git clone https://github.com/SuperInstance/counterpoint-engine-rs.git
cd counterpoint-engine-rs
cargo build

License

MIT

Part of the SuperInstance OpenConstruct ecosystem.