Higan cubic resampler

cubic.hpp

#pragma once

#include <nall/queue.hpp>

namespace nall { namespace DSP { namespace Resampler {

struct Cubic {
  inline auto reset(double inputFrequency, double outputFrequency, uint queueSize = 0) -> void;
  inline auto pending() const -> bool { return samples.pending(); }
  inline auto read() -> double { return samples.read(); }
  inline auto write(double sample) -> void;

private:
  double inputFrequency;
  double outputFrequency;

  double ratio;
  double fraction;
  double history[4];
  queue<double> samples;
};

auto Cubic::reset(double inputFrequency, double outputFrequency, uint queueSize) -> void {
  this->inputFrequency = inputFrequency;
  this->outputFrequency = outputFrequency;
  if(!queueSize) queueSize = outputFrequency * 0.02;  //20ms

  ratio = inputFrequency / outputFrequency;
  fraction = 0.0;
  for(auto& sample: history) sample = 0.0;
  samples.resize(queueSize);
}

auto Cubic::write(double sample) -> void {
  auto& mu = fraction;
  auto& s = history;

  s[0] = s[1];
  s[1] = s[2];
  s[2] = s[3];
  s[3] = sample;

  while(mu <= 1.0) {
    double A = s[3] - s[2] - s[0] + s[1];
    double B = s[0] - s[1] - A;
    double C = s[2] - s[0];
    double D = s[1];

    samples.write(A * mu * mu * mu + B * mu * mu + C * mu + D);
    mu += ratio;
  }

  mu -= 1.0;
}

}}}

queue.hpp

#pragma once

//simple circular ring buffer

namespace nall {

template<typename T>
struct queue {
  queue() = default;

  queue(const queue& source) {
    operator=(source);
  }

  queue(queue&& source) {
    operator=(move(source));
  }

  auto operator=(const queue& source) -> queue& {
    if(this == &source) return *this;
    reset();
    _size = source._size;
    _data = new T[_size];
    for(auto n : range(_size)) _data[n] = source._data[n];
    _read = source._read;
    _write = source._write;
    return *this;
  }

  auto operator=(queue&& source) -> queue& {
    if(this == &source) return *this;
    _data = source._data;
    _size = source._size;
    _read = source._read;
    _write = source._write;
    source._data = nullptr;
    source.reset();
    return *this;
  }

  ~queue() {
    reset();
  }

  explicit operator bool() const {
    return _size;
  }

  auto size() const -> uint {
    return _size;
  }

  auto data() -> T* {
    return _data;
  }

  auto data() const -> const T* {
    return _data;
  }

  auto reset() {
    delete[] _data;
    _data = nullptr;
    _size = 0;
    _read = 0;
    _write = 0;
  }

  auto resize(uint size, const T& value = {}) -> void {
    reset();
    _size = size;
    _data = new T[_size];
    for(auto n : range(_size)) _data[n] = value;
  }

  auto pending() const -> bool {
    return _read != _write;
  }

  auto read() -> T {
    T result = _data[_read];
    if(++_read >= _size) _read = 0;
    return result;
  }

  auto last() const -> T {
    return _data[_write];
  }

  auto write(const T& value) -> void {
    _data[_write] = value;
    if(++_write >= _size) _write = 0;
  }

private:
  T* _data = nullptr;
  uint _size = 0;
  uint _read = 0;
  uint _write = 0;
};

}