#ifndef HAMMINGWINDOW_HH

#define HAMMINGWINDOW_HH

#include "MemBuffer.hh"

#include "xrange.hh"

#include <cassert>

#include <cmath>

#include <map>

#include <numbers>

#include <span>

// 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, openmsx::MemBuffer<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