AnimatableVector.swift

import SwiftUI
import enum Accelerate.vDSP

public struct AnimatableVector<V: BinaryFloatingPoint>: VectorArithmetic, Hashable {
    public var values: [Double]

    public init<V: BinaryFloatingPoint>(values: [V]) {
        self.values = values.map(Double.init)
    }

    public init<V: BinaryFloatingPoint>(_ values: V...) {
        self.init(values: values)
    }

    public init() {
        self.init(values: [Double]())
    }

    public func values(_: Void = ()) -> [V] {
        return values.map(V.init)
    }
}

// MARK: - VectorArithmetic
public extension AnimatableVector {
    mutating func scale(by rhs: Double) {
        values = vDSP.multiply(rhs, values)
    }

    var magnitudeSquared: Double {
        vDSP.sum(vDSP.multiply(values, values))
    }
}

// MARK: - AdditiveArithmetic
public extension AnimatableVector {
    static var zero: Self {
        Self()
    }

    static func + (lhs: Self, rhs: Self) -> Self {
        let count = max(lhs.values.count, rhs.values.count)
        let lhs: [Double] = Array(unsafeUninitializedCapacity: count, initializingWith: zeroPadding(count: count, values: lhs.values))
        let rhs: [Double] = Array(unsafeUninitializedCapacity: count, initializingWith: zeroPadding(count: count, values: rhs.values))
        return Self(values: vDSP.add(lhs, rhs))
    }

    static func - (lhs: Self, rhs: Self) -> Self {
        let count = max(lhs.values.count, rhs.values.count)
        let lhs: [Double] = Array(unsafeUninitializedCapacity: count, initializingWith: zeroPadding(count: count, values: lhs.values))
        let rhs: [Double] = Array(unsafeUninitializedCapacity: count, initializingWith: zeroPadding(count: count, values: rhs.values))
        return Self(values: vDSP.subtract(lhs, rhs))
    }

    private static func zeroPadding(count: Int, values: [Double]) -> (_ buffer: inout UnsafeMutableBufferPointer<Double>, _ n: inout Int) -> Void {
        return { buffer, n in
            for i in 0..<count {
                buffer[i] = (i < values.count) ? values[i] : 0
            }
            n = count
        }
    }
}