MeterTableOC Swift port

MeterTable.swift

import Foundation

struct MeterTable {
    private let minDecibels: Double
    private let scaleFactor: Double
    private let table: [Double]
    
    init(minDB: Double = -80, tableSize: Int = 400, root: Double = 2) {
        self.minDecibels = minDB

        let decibelResolution = minDecibels / (Double(tableSize) - 1)
        self.scaleFactor = 1.0 / decibelResolution
        
        let minAmp = dbToAmp(minDB)
        let ampRange = 1.0 - minAmp
        let invAmpRange = 1.0 / ampRange
        let rRoot = 1.0 / root
        
        var table = [Double]()
        
        for i in 0..<tableSize {
            let decibels = Double(i) * decibelResolution
            let amp = dbToAmp(decibels)
            let adjAmp = (amp - minAmp) * invAmpRange
            table.append(pow(adjAmp, rRoot))
        }
        
        self.table = table
    }
    
    func valueAt(_ decibels: Double) -> Double {
        if decibels < minDecibels {
            return 0
        }
        
        if decibels >= 0 {
            return 1
        }
        
        let index = Int(decibels * scaleFactor)

        guard index < table.count else {
            return 1
        }

        return table[index]
    }
}

private func dbToAmp(_ db: Double) -> Double {
    pow(10, 0.05 * db)
}