static double autocorrelationOfAudioSamples(short[] samples) {
  ret autocorrelationOfAudioSamples(samples, 0, l(samples));
}

static double autocorrelationOfAudioSamples(short[] samples, int start, int end) {
  int n = end-start;
  double sum = 0;
  for j to n: {
    double correlation = 0;
    for i to n:
      correlation += sixteenBitAudioSampleToDouble(samples[start+i])
        * sixteenBitAudioSampleToDouble(samples[start+mod(i - j, n)]);
    sum += correlation;
  }
  ret doubleRatio(sum, n);
}

static double autocorrelationOfAudioSamples(short[] samples, IntRange r) {
  ret autocorrelationOfAudioSamples(samples, r.start, r.end);
}

Began life as a copy of #1026886