#include <cmath>
#include "const.h"
#include "windowsfunc.h"

void Windows::RectangleWin(double* w, int n)
{
	for (int i = 0; i < n; i++) {
		w[i] = 1;
	 }
}
void Windows::TriangularWin(double* w, int n)
{
	if (n & 1) {
		//nΪÆæÊý
		for (int i = 0; i < (n - 1) / 2; i++) {
			w[i] = 2. * (i + 1) / (n + 1);
		}
		for (int i = (n - 1) / 2; i < n; i++) {
			w[i] = 2. * (n - i) / (n + 1);
		}
	}
	else {
		for (int i = 0; i < n/ 2; i++) {
			w[i] = (2. *i + 1) / n;
		}
		for (int i = n / 2; i < n; i++) {
			w[i] = w[n - 1 - i];
		}
	}
}
void Windows::HannWin(double* w, int n)
{
	for (int i = 0; i < n; i++) {
		w[i] = 0.5 * (1 - cos(2 * pi * i / (n - 1)));
	}
}
void Windows::HammingWin(double* w, int n)
{
	for (int i = 0; i < n; i++) {
		w[i] = 0.54 - 0.46 * cos(2 * pi * i / (n - 1));
	}
}

void Windows::BlackManWin(double* w, int n)
{
	for (int i = 0; i < n; i++) {
		w[i] = 0.42 - 0.5 * cos(2 * pi * i / (n - 1)) 
			+ 0.08 * cos(4 * pi * i / (n - 1));
	}
}
double Windows::besseli(double x, int n_terms )
{
	double sum = 1.0;
	double term = 1.0;
	double x_sq_half = x * x / 4.0; // (x/2)^2

	for (int k = 1; k < n_terms; k++) {
		term *= x_sq_half / (k * k);
		sum += term;

		// Èç¹ûÏî±äµÃ·Ç³£Ð¡£¬ÌáÇ°ÖÕÖ¹ÒÔÌá¸ßЧÂÊ
		if (term < 1e-15 * sum) {
			break;
		}
	}

	return sum;
}

void Windows::KaiserWin(double* w, int n, double beta )
{
	double theta;
	// ¼ÆËã·ÖĸµÄ±´Èû¶ûº¯ÊýÖµ£¨Ö»Ðè¼ÆËãÒ»´Î£©
	double denominator = besseli(beta);

	for (int i = 0; i < n; i++) {
		// ¼ÆËã²ÎÊý£º½«Ë÷ÒýÓ³Éäµ½ [-1, 1] Çø¼ä
		double argument = (2.0 * i) / (n - 1) - 1.0;

		theta = beta * sqrt(1 - argument * argument);
		w[i] = besseli(theta) / denominator;
	}
}