Generate the I and Q components for a local oscillator

IQ_Oscillator.swift

import Foundation

/*
  Generate the I and Q components for a local oscillator
*/

public class IQ_Oscillator {
  
  let tau = 2 * Double.pi
  
  let dphi : Double
  var phi  : Double = 0
  
  
  public init(frequency: Double, sampleRate: Double) {
    // compute phase increment per sample
    dphi = (tau / sampleRate) * frequency
  }
  
  public func sample() -> (i: Double, q: Double) {
    
    let i = cos(phi)
    let q = sin(phi)
    
    phi += dphi
    if phi >= tau { phi -= tau }  // don't let this accumulate, error becmes large
    
    return (i, q)
  }
  
}