hammingWindow.hh

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#ifndef HAMMINGWINDOW_HH
#define HAMMINGWINDOW_HH
 
#include "xrange.hh"
 
#include <cassert>
#include <cmath>
#include <map>
#include <numbers>
#include <span>
#include <vector>
 
// Returns the coefficients of the 'hamming' window of length 'n'.
//     https://en.wikipedia.org/wiki/Window_function#Hann_and_Hamming_windows
inline std::span<const float> hammingWindow(unsigned n)
{
        static std::map<unsigned, std::vector<float>> cache;
        auto [it, inserted] = cache.try_emplace(n);
        auto& window = it->second;
 
        if (inserted) {
                window.resize(n);
                for (auto i : xrange(n)) {
                        window[i] = float(0.53836 - 0.46164 * cos(2 * std::numbers::pi * i / (n - 1)));
                }
                return window;
        }
 
        assert(window.size() == n);
        return window;
}
 
#endif