using System;
using System.Collections.Generic;
using System.Text;

namespace SDR
{
    class Affilter
    {
        static double[] a;   //IIRフィルター係数 
        static double[] b;   //IIRフィルター係数 
        static double[] iirin;  //フィルター計算用入力信号バッファ
        static double[] iirout;  //フィルター計算用出力信号バッファ
      
       static double PI = 3.141592653589793238;   // パイの値
       static  double[] bpfrealout;   //AF BPF出力信号の保存バッファ(実部)
       

        //IIR Filterの初期化と係数計算
        public  static void CreateIirAfBpf(double Fcenter, double Bw, double SamplFreq) //引数は後に使用予定
        {
            a = new double[3];      //AF BPF係数用バッファ
            b = new double[3];      //AF BPF係数用バッファ
           iirin = new double[3];      //AF BPF計算用バッファ
           iirout = new double[3];      //AF BPF計算用バッファ
           Array.Clear(iirin, 0, 3);    //配列クリア
           Array.Clear(iirout, 0, 3);    //配列クリア

            double omega =  2.0 * PI * 500 / 48000;  //フィルタ係数計算で使用する中間値
           // double alpha = Math.Sin(omega) * Math.Sinh(Math.Log(2.0) / 2.0 * Bw * omega / Math.Sin(omega));
            double alpha = Math.Sin(omega) / 0.667;
           
            //ここからHS_BPF係数
            //b[2] = (1.0 - Math.Cos(omega)) / 2.0;
            a[0] = 1.0;
            b[0] = 0.046932511068243;
            b[1] = 0.0;
            b[2] = -0.0469325110682464;
            a[1] = -1.90205051664252;
            a[2] = 0.90613497786351;

        }

        //実信号にAF BPFを適応する
        public static void IirAfFilter(double[] real)
        {
           
            bpfrealout = new double[1024];      //AF BPF出力用バッファ
         

            for (int i = 0; i < 1024; i++)  //1024信号繰り返す
            {
                iirin[0] = real[i];
             
                bpfrealout[i] = b[0] / a[0] * iirin[0] + b[1] / a[0] * iirin[1] + b[2] / a[0] * iirin[2] - a[1] / a[0] * iirout[1]
                 - a[2] / a[0] * iirout[2];
               iirin[2] = iirin[1];  //2つ前の入力信号を更新
               iirin[1] = real[i];  //1つ前の入力信号を更新
               iirout[2] = iirout[1];  //2つ前のout信号を更新
               iirout[1] = bpfrealout[i];  //1つ前のout信号を更新

                real[i] =  bpfrealout[i];
            }
        }

    }
}