math.h

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// https://AudioProcessingFramework.github.io/
 
 
#ifndef APF_MATH_H
#define APF_MATH_H
 
#include <cmath>  // for std::pow(), ...
#include <iterator> // for std::iterator_traits
#include <numeric>  // for std::accumulate()
#include <algorithm>  // for std::max()
 
namespace apf
{
namespace math
{
 
template<typename T> constexpr T pi();
 
template<>
constexpr float pi<float>()
{
  // 9 digits are needed for float, 17 digits for double, 21 for long double
  // TODO: But this may be different on other hardware platforms ...?
  return 3.1415926535897932384626433832795f;
}
 
template<>
constexpr double pi<double>()
{
  return 3.1415926535897932384626433832795;
}
 
template<>
constexpr long double pi<long double>()
{
  return 3.1415926535897932384626433832795l;
}
 
template<typename T>
inline T pi_div_180()
{
  // local variable to avoid warning message about conversion
  T q = 180;
  return pi<T>() / q;
}
 
template<typename T> inline T square(T x) { return x*x; }
 
template<typename T>
inline T dB2linear(T L, bool power = false)
{
  T f = 20; if (power) f = 10;
  T base = 10;
  return std::pow(base, L / f);
}
 
template<typename T>
inline T linear2dB(T x, bool power = false)
{
  T f = 20; if (power) f = 10;
  return f * std::log10(x);
}
 
template<typename T>
inline T deg2rad(T angle)
{
  return angle * pi_div_180<T>();
}
 
template<typename T>
inline T rad2deg(T angle)
{
  return angle / pi_div_180<T>();
}
 
template<typename T>
inline T fwrap(T x, T full)
{
  x = std::fmod(x, full);
  if (x < 0) x += full;
  return x;
}
 
template<typename T>
inline T wrap(T x, T full)
{
  x %= full;
  if (x < 0) x += full;
  return x;
}
 
template<>
inline float wrap(float x, float full)
{
  return fwrap(x, full);
}
 
template<>
inline double wrap(double x, double full)
{
  return fwrap(x, full);
}
 
template<>
inline long double wrap(long double x, long double full)
{
  return fwrap(x, full);
}
 
template<typename T>
inline T wrap_two_pi(T x)
{
  // local variable to avoid warning message about conversion
  T two = 2;
  return wrap(x, two * pi<T>());
}
 
template<typename T>
inline T next_power_of_2(T number)
{
  T power_of_2 = 1;
  while (power_of_2 < number) power_of_2 *= 2;
  return power_of_2;
}
 
template<typename I>
inline typename std::iterator_traits<I>::value_type
max_amplitude(I begin, I end)
{
  using T = typename std::iterator_traits<I>::value_type;
  return std::accumulate(begin, end, T()
      , [] (T current, T next) { return std::max(current, std::abs(next)); });
}
 
template<typename I>
inline typename std::iterator_traits<I>::value_type rms(I begin, I end)
{
  using T = typename std::iterator_traits<I>::value_type;
 
  // inner product: sum of squares
  // divided by number: mean
  // sqrt: root
  return std::sqrt(std::inner_product(begin, end, begin, T())
      / static_cast<T>(std::distance(begin, end)));
}
 
template<typename I>
bool has_only_zeros(I first, I last)
{
  while (first != last) if (*first++ != 0) return false;
  return true;
}
 
template<typename T>
class raised_cosine
{
  public:
    using argument_type = T;
    using result_type = T;
 
    explicit raised_cosine(T period = 0) : _period(period) {}
 
    T operator()(T in) const
    {
      // local variable to avoid warning about conversion
      T half = 0.5;
      return std::cos(in * 2 * pi<T>() / _period) * half + half;
    }
 
  private:
    const T _period;
};
 
template<typename T, typename U = T>
class linear_interpolator
{
  public:
    using argument_type = U;
    using result_type = T;
 
    linear_interpolator() : _first(), _increment() {}
 
    linear_interpolator(result_type first, result_type last
        , argument_type length = argument_type(1))
    {
      this->set(first, last, length);
    }
 
    void set(result_type first, result_type last
        , argument_type length = argument_type(1))
    {
      _first = first;
      _increment = (last - first) / length;
    }
 
    result_type operator()(argument_type x)
    {
      return _first + result_type(x) * _increment;
    }
 
  private:
    result_type _first, _increment;
};
 
template<typename T>
linear_interpolator<T>
make_linear_interpolator(T first, T last)
{
  return linear_interpolator<T>(first, last);
}
 
template<typename T, typename U>
linear_interpolator<T, U>
make_linear_interpolator(T first, T last, U length)
{
  return linear_interpolator<T, U>(first, last, length);
}
 
template<typename T>
struct identity { const T& operator()(const T& in) { return in; } };
 
}  // namespace math
}  // namespace apf
 
#endif