MirUtils.cpp

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/*  SPDX-License-Identifier: GPL-2.0-or-later */
/*!********************************************************************
 
  Audacity: A Digital Audio Editor
 
  MirUtils.cpp
 
  Matthieu Hodgkinson
 
**********************************************************************/
#include "MirUtils.h"
 
#include <cmath>
#include <numeric>
 
namespace MIR
{
namespace
{
constexpr auto bpmStdDev = 29.7953;
constexpr auto pi = 3.141592653589793;
 
constexpr bool IsPrimeDecompositionTwoThreeOnly(int n)
{
   while (n % 2 == 0)
      n /= 2;
   while (n % 3 == 0)
      n /= 3;
   return n == 1;
}
 
static_assert(IsPrimeDecompositionTwoThreeOnly(1));
static_assert(IsPrimeDecompositionTwoThreeOnly(2));
static_assert(IsPrimeDecompositionTwoThreeOnly(3));
static_assert(IsPrimeDecompositionTwoThreeOnly(4));
static_assert(!IsPrimeDecompositionTwoThreeOnly(5));
static_assert(IsPrimeDecompositionTwoThreeOnly(6));
static_assert(!IsPrimeDecompositionTwoThreeOnly(7));
static_assert(IsPrimeDecompositionTwoThreeOnly(8));
static_assert(IsPrimeDecompositionTwoThreeOnly(9));
 
// Function to generate numbers whose prime factorization contains only twos or
// threes
std::vector<int> GetPowersOf2And3(int lower, int upper)
{
   std::vector<int> result;
   for (int i = lower; i <= upper; ++i)
      if (IsPrimeDecompositionTwoThreeOnly(i))
         result.push_back(i);
   return result;
}
} // namespace
 
std::vector<int> GetPossibleBarDivisors(int lower, int upper)
{
   auto result = GetPowersOf2And3(lower, upper);
   // Remove divisors that have more than two triplet levels. E.g. 3/4s are
   // okay, 3/4s with swung ryhthms too, but beyond that it's probably very rare
   // (e.g. swung 9/8 ??...)
   result.erase(
      std::remove_if(
         result.begin(), result.end(), [](int n) { return n % 27 == 0; }),
      result.end());
   return result;
}
 
std::vector<int> GetPeakIndices(const std::vector<float>& x)
{
   std::vector<int> peakIndices;
   for (auto j = 0; j < x.size(); ++j)
   {
      const auto i = j == 0 ? x.size() - 1 : j - 1;
      const auto k = j == x.size() - 1 ? 0 : j + 1;
      if (x[i] < x[j] && x[j] > x[k])
         peakIndices.push_back(j);
   }
   return peakIndices;
}
 
std::vector<float> GetNormalizedHann(int size)
{
   std::vector<float> window(size);
   for (auto n = 0; n < size; ++n)
      window[n] = .5 * (1 - std::cos(2 * pi * n / size));
   const auto windowSum = std::accumulate(window.begin(), window.end(), 0.f);
   std::transform(
      window.begin(), window.end(), window.begin(),
      [windowSum](float w) { return w / windowSum; });
   return window;
}
} // namespace MIR