Arduino frequency counter ring buffer

ringbuf_counter.hpp

// we expect a timeslice to be 1024 micros
static constexpr uint32_t TIMESLICE_LEN_US = 1024;

struct ringbuf_counter {
  // must be power of 2
  static constexpr int NDATA = 512;
  uint16_t data[NDATA];
  int start = 0;
  int idx = 0;
  int n = 0;
  uint32_t running_sum = 0;

  void record_count(uint16_t x) {
    if (n >= NDATA) running_sum -= data[idx];
    running_sum += x;
    data[idx] = x;
    idx = (idx + 1) & (NDATA - 1);
    if (n < NDATA) ++n;
  }

  uint32_t get_sum() {
    return running_sum;
  }

  uint32_t estimate_frequency() {
    if (n == 0) return 0;
    uint64_t sum = get_sum() * 1000000;
    uint64_t interval_us = TIMESLICE_LEN_US * n;

    uint64_t fudge = 1 + TIMESLICE_LEN_US / 2; // round the result
    return (sum + fudge) / interval_us;
  }
};