// This class based on the Resampler that is part of Cockos WDL
// originally written in C++ and ported to C# for NAudio by Mark Heath
// Used in NAudio with permission from Justin Frankel
// Original WDL License:
//     Copyright (C) 2005 and later Cockos Incorporated
//     
//     Portions copyright other contributors, see each source file for more information
// 
//     This software is provided 'as-is', without any express or implied
//     warranty.  In no event will the authors be held liable for any damages
//     arising from the use of this software.
// 
//     Permission is granted to anyone to use this software for any purpose,
//     including commercial applications, and to alter it and redistribute it
//     freely, subject to the following restrictions:
// 
//     1. The origin of this software must not be misrepresented; you must not
//        claim that you wrote the original software. If you use this software
//        in a product, an acknowledgment in the product documentation would be
//        appreciated but is not required.
//     2. Altered source versions must be plainly marked as such, and must not be
//        misrepresented as being the original software.
//     3. This notice may not be removed or altered from any source distribution.


using System;

// default to floats for audio samples
using WDL_ResampleSample = System.Single; // n.b. default in WDL is double

// default to floats for sinc filter ceofficients
using WDL_SincFilterSample = System.Single; // can also be set to double

namespace NAudio.Dsp
{
    /// <summary>
    /// Fully managed resampler, based on Cockos WDL Resampler
    /// </summary>
    class WdlResampler
    {
        private const int WDL_RESAMPLE_MAX_FILTERS = 4;
        private const int WDL_RESAMPLE_MAX_NCH = 64;
        private const double PI = 3.1415926535897932384626433832795;

        /// <summary>
        /// Creates a new Resampler
        /// </summary>
        public WdlResampler()
        {
            m_filterq = 0.707f;
            m_filterpos = 0.693f; // .792 ?

            m_sincoversize = 0;
            m_lp_oversize = 1;
            m_sincsize = 0;
            m_filtercnt = 1;
            m_interp = true;
            m_feedmode = false;

            m_filter_coeffs_size = 0;
            m_sratein = 44100.0;
            m_srateout = 44100.0;
            m_ratio = 1.0;
            m_filter_ratio = -1.0;

            Reset();
        }

        /// <summary>
        /// sets the mode
        /// if sinc set, it overrides interp or filtercnt
        /// </summary>
        public void SetMode(bool interp, int filtercnt, bool sinc, int sinc_size = 64, int sinc_interpsize = 32)
        {
            m_sincsize = sinc && sinc_size >= 4 ? sinc_size > 8192 ? 8192 : sinc_size : 0;
            m_sincoversize = (m_sincsize != 0) ? (sinc_interpsize <= 1 ? 1 : sinc_interpsize >= 4096 ? 4096 : sinc_interpsize) : 1;

            m_filtercnt = (m_sincsize != 0) ? 0 : (filtercnt <= 0 ? 0 : filtercnt >= WDL_RESAMPLE_MAX_FILTERS ? WDL_RESAMPLE_MAX_FILTERS : filtercnt);
            m_interp = interp && (m_sincsize == 0);

            //Debug.WriteLine(String.Format("setting interp={0}, filtercnt={1}, sinc={2},{3}\n", m_interp, m_filtercnt, m_sincsize, m_sincoversize));

            if (m_sincsize == 0)
            {
                m_filter_coeffs = new WDL_SincFilterSample[0]; //.Resize(0);
                m_filter_coeffs_size = 0;
            }
            if (m_filtercnt == 0)
            {
                m_iirfilter = null;
            }
        }

        /// <summary>
        /// Sets the filter parameters
        /// used for filtercnt>0 but not sinc
        /// </summary>
        public void SetFilterParms(float filterpos = 0.693f, float filterq = 0.707f)
        {
            m_filterpos = filterpos;
            m_filterq = filterq;
        }

        /// <summary>
        /// Set feed mode
        /// </summary>
        /// <param name="wantInputDriven">if true, that means the first parameter to ResamplePrepare will specify however much input you have, not how much you want</param>
        public void SetFeedMode(bool wantInputDriven)
        {
            m_feedmode = wantInputDriven;
        }

        /// <summary>
        /// Reset
        /// </summary>
        public void Reset(double fracpos = 0.0)
        {
            m_last_requested = 0;
            m_filtlatency = 0;
            m_fracpos = fracpos;
            m_samples_in_rsinbuf = 0;
            if (m_iirfilter != null) m_iirfilter.Reset();
        }

        public void SetRates(double rate_in, double rate_out)
        {
            if (rate_in < 1.0) rate_in = 1.0;
            if (rate_out < 1.0) rate_out = 1.0;
            if (rate_in != m_sratein || rate_out != m_srateout)
            {
                m_sratein = rate_in;
                m_srateout = rate_out;
                m_ratio = m_sratein / m_srateout;
            }
        }

        // amount of input that has been received but not yet converted to output, in seconds
        public double GetCurrentLatency()
        {
            double v = ((double)m_samples_in_rsinbuf - m_filtlatency) / m_sratein;

            if (v < 0.0) v = 0.0;
            return v;
        }

        /// <summary>
        /// Prepare
        /// note that it is safe to call ResamplePrepare without calling ResampleOut (the next call of ResamplePrepare will function as normal)
        /// nb inbuffer was WDL_ResampleSample **, returning a place to put the in buffer, so we return a buffer and offset
        /// </summary>
        /// <param name="out_samples">req_samples is output samples desired if !wantInputDriven, or if wantInputDriven is input samples that we have</param>
        /// <param name="nch"></param>
        /// <param name="inbuffer"></param>
        /// <param name="inbufferOffset"></param>
        /// <returns>returns number of samples desired (put these into *inbuffer)</returns>
        public int ResamplePrepare(int out_samples, int nch, out WDL_ResampleSample[] inbuffer, out int inbufferOffset)
        {
            if (nch > WDL_RESAMPLE_MAX_NCH || nch < 1)
            {
                inbuffer = null;
                inbufferOffset = 0;
                return 0;
            }

            int fsize = 0;
            if (m_sincsize > 1)
            {
                fsize = m_sincsize;
            }

            int hfs = fsize / 2;
            if (hfs > 1 && m_samples_in_rsinbuf < hfs - 1)
            {
                m_filtlatency += hfs - 1 - m_samples_in_rsinbuf;

                m_samples_in_rsinbuf = hfs - 1;

                if (m_samples_in_rsinbuf > 0)
                {
                    m_rsinbuf = new WDL_SincFilterSample[m_samples_in_rsinbuf * nch];
                }
            }

            int sreq = 0;

            if (!m_feedmode) sreq = (int)(m_ratio * out_samples) + 4 + fsize - m_samples_in_rsinbuf;
            else sreq = out_samples;

            if (sreq < 0) sreq = 0;

        again:
            Array.Resize(ref m_rsinbuf, (m_samples_in_rsinbuf + sreq) * nch);

            int sz = m_rsinbuf.Length / ((nch != 0) ? nch : 1) - m_samples_in_rsinbuf;
            if (sz != sreq)
            {
                if (sreq > 4 && (sz == 0))
                {
                    sreq /= 2;
                    goto again; // try again with half the size
                }
                // todo: notify of error?
                sreq = sz;
            }

            inbuffer = m_rsinbuf;
            inbufferOffset = m_samples_in_rsinbuf * nch;

            m_last_requested = sreq;
            return sreq;
        }

        // if numsamples_in < the value return by ResamplePrepare(), then it will be flushed to produce all remaining valid samples
        // do NOT call with nsamples_in greater than the value returned from resamplerprpare()! the extra samples will be ignored.
        // returns number of samples successfully outputted to out
        public int ResampleOut(WDL_ResampleSample[] outBuffer, int outBufferIndex, int nsamples_in, int nsamples_out, int nch)
        {
            if (nch > WDL_RESAMPLE_MAX_NCH || nch < 1)
            {
                return 0;
            }

            if (m_filtercnt > 0)
            {
                if (m_ratio > 1.0 && nsamples_in > 0) // filter input
                {
                    if (m_iirfilter == null) m_iirfilter = new WDL_Resampler_IIRFilter();

                    int n = m_filtercnt;
                    m_iirfilter.setParms((1.0 / m_ratio) * m_filterpos, m_filterq);

                    int bufIndex = m_samples_in_rsinbuf * nch;
                    int a, x;
                    int offs = 0;
                    for (x = 0; x < nch; x++)
                        for (a = 0; a < n; a++)
                            m_iirfilter.Apply(m_rsinbuf, bufIndex + x, m_rsinbuf, bufIndex + x, nsamples_in, nch, offs++);
                }
            }

            m_samples_in_rsinbuf += Math.Min(nsamples_in, m_last_requested); // prevent the user from corrupting the internal state


            int rsinbuf_availtemp = m_samples_in_rsinbuf;

            if (nsamples_in < m_last_requested) // flush out to ensure we can deliver
            {
                int fsize = (m_last_requested - nsamples_in) * 2 + m_sincsize * 2;

                int alloc_size = (m_samples_in_rsinbuf + fsize) * nch;
                Array.Resize(ref m_rsinbuf, alloc_size);
                if (m_rsinbuf.Length == alloc_size)
                {
                    Array.Clear(m_rsinbuf, m_samples_in_rsinbuf * nch, fsize * nch);
                    rsinbuf_availtemp = m_samples_in_rsinbuf + fsize;
                }
            }

            int ret = 0;
            double srcpos = m_fracpos;
            double drspos = m_ratio;
            int localin = 0; // localin is an index into m_rsinbuf

            int outptr = outBufferIndex;  // outptr is an index into  outBuffer;

            int ns = nsamples_out;

            int outlatadj = 0;

            if (m_sincsize != 0) // sinc interpolating
            {
                if (m_ratio > 1.0) BuildLowPass(1.0 / (m_ratio * 1.03));
                else BuildLowPass(1.0);

                int filtsz = m_filter_coeffs_size;
                int filtlen = rsinbuf_availtemp - filtsz;
                outlatadj = filtsz / 2 - 1;
                int filter = 0; // filter is an index into m_filter_coeffs m_filter_coeffs.Get();

                if (nch == 1)
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;

                        if (ipos >= filtlen - 1) break; // quit decoding, not enough input samples

                        SincSample1(outBuffer, outptr, m_rsinbuf, localin + ipos, srcpos - ipos, m_filter_coeffs, filter, filtsz);
                        outptr++;
                        srcpos += drspos;
                        ret++;
                    }
                }
                else if (nch == 2)
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;

                        if (ipos >= filtlen - 1) break; // quit decoding, not enough input samples

                        SincSample2(outBuffer, outptr, m_rsinbuf, localin + ipos * 2, srcpos - ipos, m_filter_coeffs, filter, filtsz);
                        outptr += 2;
                        srcpos += drspos;
                        ret++;
                    }
                }
                else
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;

                        if (ipos >= filtlen - 1) break; // quit decoding, not enough input samples

                        SincSample(outBuffer, outptr, m_rsinbuf, localin + ipos * nch, srcpos - ipos, nch, m_filter_coeffs, filter, filtsz);
                        outptr += nch;
                        srcpos += drspos;
                        ret++;
                    }
                }
            }
            else if (!m_interp) // point sampling
            {
                if (nch == 1)
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;
                        if (ipos >= rsinbuf_availtemp) break; // quit decoding, not enough input samples

                        outBuffer[outptr++] = m_rsinbuf[localin + ipos];
                        srcpos += drspos;
                        ret++;
                    }
                }
                else if (nch == 2)
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;
                        if (ipos >= rsinbuf_availtemp) break; // quit decoding, not enough input samples

                        ipos += ipos;

                        outBuffer[outptr + 0] = m_rsinbuf[localin + ipos];
                        outBuffer[outptr + 1] = m_rsinbuf[localin + ipos + 1];
                        outptr += 2;
                        srcpos += drspos;
                        ret++;
                    }
                }
                else
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;
                        if (ipos >= rsinbuf_availtemp) break; // quit decoding, not enough input samples

                        Array.Copy(m_rsinbuf, localin + ipos * nch, outBuffer, outptr, nch);
                        outptr += nch;
                        srcpos += drspos;
                        ret++;
                    }
            }
            else // linear interpolation
            {
                if (nch == 1)
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;
                        double fracpos = srcpos - ipos;

                        if (ipos >= rsinbuf_availtemp - 1)
                        {
                            break; // quit decoding, not enough input samples
                        }

                        double ifracpos = 1.0 - fracpos;
                        int inptr = localin + ipos;
                        outBuffer[outptr++] = (WDL_ResampleSample)(m_rsinbuf[inptr] * (ifracpos) + m_rsinbuf[inptr + 1] * (fracpos));
                        srcpos += drspos;
                        ret++;
                    }
                }
                else if (nch == 2)
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;
                        double fracpos = srcpos - ipos;

                        if (ipos >= rsinbuf_availtemp - 1)
                        {
                            break; // quit decoding, not enough input samples
                        }

                        double ifracpos = 1.0 - fracpos;
                        int inptr = localin + ipos * 2;
                        outBuffer[outptr + 0] = (WDL_ResampleSample)(m_rsinbuf[inptr] * (ifracpos) + m_rsinbuf[inptr + 2] * (fracpos));
                        outBuffer[outptr + 1] = (WDL_ResampleSample)(m_rsinbuf[inptr + 1] * (ifracpos) + m_rsinbuf[inptr + 3] * (fracpos));
                        outptr += 2;
                        srcpos += drspos;
                        ret++;
                    }
                }
                else
                {
                    while (ns-- != 0)
                    {
                        int ipos = (int)srcpos;
                        double fracpos = srcpos - ipos;

                        if (ipos >= rsinbuf_availtemp - 1)
                        {
                            break; // quit decoding, not enough input samples
                        }

                        double ifracpos = 1.0 - fracpos;
                        int ch = nch;
                        int inptr = localin + ipos * nch;
                        while (ch-- != 0)
                        {
                            outBuffer[outptr++] = (WDL_ResampleSample)(m_rsinbuf[inptr] * (ifracpos) + m_rsinbuf[inptr + nch] * (fracpos));
                            inptr++;
                        }
                        srcpos += drspos;
                        ret++;
                    }
                }
            }

            if (m_filtercnt > 0)
            {
                if (m_ratio < 1.0 && ret > 0) // filter output
                {
                    if (m_iirfilter == null) m_iirfilter = new WDL_Resampler_IIRFilter();
                    int n = m_filtercnt;
                    m_iirfilter.setParms(m_ratio * m_filterpos, m_filterq);

                    int x, a;
                    int offs = 0;
                    for (x = 0; x < nch; x++)
                        for (a = 0; a < n; a++)
                            m_iirfilter.Apply(outBuffer, x, outBuffer, x, ret, nch, offs++);
                }
            }

            if (ret > 0 && rsinbuf_availtemp > m_samples_in_rsinbuf) // we had to pad!!
            {
                // check for the case where rsinbuf_availtemp>m_samples_in_rsinbuf, decrease ret down to actual valid samples
                double adj = (srcpos - m_samples_in_rsinbuf + outlatadj) / drspos;
                if (adj > 0)
                {
                    ret -= (int)(adj + 0.5);
                    if (ret < 0) ret = 0;
                }
            }

            int isrcpos = (int)srcpos;
            m_fracpos = srcpos - isrcpos;
            m_samples_in_rsinbuf -= isrcpos;
            if (m_samples_in_rsinbuf <= 0)
            {
                m_samples_in_rsinbuf = 0;
            }
            else
            {
                // TODO: bug here
                Array.Copy(m_rsinbuf, localin + isrcpos * nch, m_rsinbuf, localin, m_samples_in_rsinbuf * nch);
            }



            return ret;
        }

        // only called in sinc modes
        private void BuildLowPass(double filtpos)
        {
            int wantsize = m_sincsize;
            int wantinterp = m_sincoversize;

            if (m_filter_ratio != filtpos ||
                m_filter_coeffs_size != wantsize ||
                m_lp_oversize != wantinterp)
            {
                m_lp_oversize = wantinterp;
                m_filter_ratio = filtpos;

                // build lowpass filter
                int allocsize = (wantsize + 1) * m_lp_oversize;
                Array.Resize(ref m_filter_coeffs, allocsize);
                //int cfout = 0; // this is an index into m_filter_coeffs
                if (m_filter_coeffs.Length == allocsize)
                {
                    m_filter_coeffs_size = wantsize;

                    int sz = wantsize * m_lp_oversize;
                    int hsz = sz / 2;
                    double filtpower = 0.0;
                    double windowpos = 0.0;
                    double dwindowpos = 2.0 * PI / (double)(sz);
                    double dsincpos = PI / m_lp_oversize * filtpos; // filtpos is outrate/inrate, i.e. 0.5 is going to half rate
                    double sincpos = dsincpos * (double)(-hsz);

                    int x;
                    for (x = -hsz; x < hsz + m_lp_oversize; x++)
                    {
                        double val = 0.35875 - 0.48829 * Math.Cos(windowpos) + 0.14128 * Math.Cos(2 * windowpos) - 0.01168 * Math.Cos(6 * windowpos); // blackman-harris
                        if (x != 0) val *= Math.Sin(sincpos) / sincpos;

                        windowpos += dwindowpos;
                        sincpos += dsincpos;

                        m_filter_coeffs[hsz + x] = (WDL_SincFilterSample)val;
                        if (x < hsz) filtpower += val;
                    }
                    filtpower = m_lp_oversize / filtpower;
                    for (x = 0; x < sz + m_lp_oversize; x++)
                    {
                        m_filter_coeffs[x] = (WDL_SincFilterSample)(m_filter_coeffs[x] * filtpower);
                    }
                }
                else m_filter_coeffs_size = 0;

            }
        }

        // SincSample(WDL_ResampleSample *outptr, WDL_ResampleSample *inptr, double fracpos, int nch, WDL_SincFilterSample *filter, int filtsz)
        private void SincSample(WDL_ResampleSample[] outBuffer, int outBufferIndex, WDL_ResampleSample[] inBuffer, int inBufferIndex, double fracpos, int nch, WDL_SincFilterSample[] filter, int filterIndex, int filtsz)
        {
            int oversize = m_lp_oversize;
            fracpos *= oversize;
            int ifpos = (int)fracpos;
            filterIndex += oversize - 1 - ifpos;
            fracpos -= ifpos;

            for (int x = 0; x < nch; x++)
            {
                double sum = 0.0, sum2 = 0.0;
                int fptr = filterIndex;
                int iptr = inBufferIndex + x;
                int i = filtsz;
                while (i-- != 0)
                {
                    sum += filter[fptr] * inBuffer[iptr];
                    sum2 += filter[fptr + 1] * inBuffer[iptr];
                    iptr += nch;
                    fptr += oversize;
                }
                outBuffer[outBufferIndex + x] = (WDL_ResampleSample)(sum * fracpos + sum2 * (1.0 - fracpos));
            }
        }

        // SincSample1(WDL_ResampleSample* outptr, WDL_ResampleSample* inptr, double fracpos, WDL_SincFilterSample* filter, int filtsz)
        private void SincSample1(WDL_ResampleSample[] outBuffer, int outBufferIndex, WDL_ResampleSample[] inBuffer, int inBufferIndex, double fracpos, WDL_SincFilterSample[] filter, int filterIndex, int filtsz)
        {
            int oversize = m_lp_oversize;
            fracpos *= oversize;
            int ifpos = (int)fracpos;
            filterIndex += oversize - 1 - ifpos;
            fracpos -= ifpos;

            double sum = 0.0, sum2 = 0.0;
            int fptr = filterIndex;
            int iptr = inBufferIndex;
            int i = filtsz;
            while (i-- != 0)
            {
                sum += filter[fptr] * inBuffer[iptr];
                sum2 += filter[fptr + 1] * inBuffer[iptr];
                iptr++;
                fptr += oversize;
            }
            outBuffer[outBufferIndex] = (WDL_ResampleSample)(sum * fracpos + sum2 * (1.0 - fracpos));
        }

        // SincSample2(WDL_ResampleSample* outptr, WDL_ResampleSample* inptr, double fracpos, WDL_SincFilterSample* filter, int filtsz)
        private void SincSample2(WDL_ResampleSample[] outptr, int outBufferIndex, WDL_ResampleSample[] inBuffer, int inBufferIndex, double fracpos, WDL_SincFilterSample[] filter, int filterIndex, int filtsz)
        {
            int oversize = m_lp_oversize;
            fracpos *= oversize;
            int ifpos = (int)fracpos;
            filterIndex += oversize - 1 - ifpos;
            fracpos -= ifpos;

            double sum = 0.0;
            double sum2 = 0.0;
            double sumb = 0.0;
            double sum2b = 0.0;
            int fptr = filterIndex;
            int iptr = inBufferIndex;
            int i = filtsz / 2;
            while (i-- != 0)
            {
                sum += filter[fptr] * inBuffer[iptr];
                sum2 += filter[fptr] * inBuffer[iptr + 1];
                sumb += filter[fptr + 1] * inBuffer[iptr];
                sum2b += filter[fptr + 1] * inBuffer[iptr + 1];
                sum += filter[fptr + oversize] * inBuffer[iptr + 2];
                sum2 += filter[fptr + oversize] * inBuffer[iptr + 3];
                sumb += filter[fptr + oversize + 1] * inBuffer[iptr + 2];
                sum2b += filter[fptr + oversize + 1] * inBuffer[iptr + 3];
                iptr += 4;
                fptr += oversize * 2;
            }
            outptr[outBufferIndex + 0] = (WDL_ResampleSample)(sum * fracpos + sumb * (1.0 - fracpos));
            outptr[outBufferIndex + 1] = (WDL_ResampleSample)(sum2 * fracpos + sum2b * (1.0 - fracpos));
        }

        private double m_sratein; // WDL_FIXALIGN
        private double m_srateout;
        private double m_fracpos;
        private double m_ratio;
        private double m_filter_ratio;
        private float m_filterq, m_filterpos;
        private WDL_ResampleSample[] m_rsinbuf; // WDL_TypedBuf<WDL_ResampleSample>
        private WDL_SincFilterSample[] m_filter_coeffs; // WDL_TypedBuf<WDL_SincFilterSample>

        private WDL_Resampler_IIRFilter m_iirfilter; // WDL_Resampler_IIRFilter *

        private int m_filter_coeffs_size;
        private int m_last_requested;
        private int m_filtlatency;
        private int m_samples_in_rsinbuf;
        private int m_lp_oversize;

        private int m_sincsize;
        private int m_filtercnt;
        private int m_sincoversize;
        private bool m_interp;
        private bool m_feedmode;



        class WDL_Resampler_IIRFilter
        {
            public WDL_Resampler_IIRFilter()
            {
                m_fpos = -1;
                Reset();
            }

            public void Reset()
            {
                m_hist = new double[WDL_RESAMPLE_MAX_FILTERS * WDL_RESAMPLE_MAX_NCH, 4];
            }

            public void setParms(double fpos, double Q)
            {
                if (Math.Abs(fpos - m_fpos) < 0.000001) return;
                m_fpos = fpos;

                double pos = fpos * PI;
                double cpos = Math.Cos(pos);
                double spos = Math.Sin(pos);

                double alpha = spos / (2.0 * Q);

                double sc = 1.0 / (1 + alpha);
                m_b1 = (1 - cpos) * sc;
                m_b2 = m_b0 = m_b1 * 0.5;
                m_a1 = -2 * cpos * sc;
                m_a2 = (1 - alpha) * sc;

            }

            public void Apply(WDL_ResampleSample[] inBuffer, int inIndex, WDL_ResampleSample[] outBuffer, int outIndex, int ns, int span, int w)
            {
                double b0 = m_b0, b1 = m_b1, b2 = m_b2, a1 = m_a1, a2 = m_a2;

                while (ns-- != 0)
                {
                    double inx = inBuffer[inIndex];
                    inIndex += span;
                    double outx = (double)(inx * b0 + m_hist[w, 0] * b1 + m_hist[w, 1] * b2 - m_hist[w, 2] * a1 - m_hist[w, 3] * a2);
                    m_hist[w, 1] = m_hist[w, 0];
                    m_hist[w, 0] = inx;
                    m_hist[w, 3] = m_hist[w, 2];
                    m_hist[w, 2] = denormal_filter(outx);
                    outBuffer[outIndex] = (WDL_ResampleSample)m_hist[w, 2];

                    outIndex += span;
                }
            }

            double denormal_filter(float x)
            {
                // TODO: implement denormalisation
                return x;
            }
            double denormal_filter(double x)
            {
                // TODO: implement denormalisation
                return x;
            }

            private double m_fpos;
            private double m_a1, m_a2;
            private double m_b0, m_b1, m_b2;
            private double[,] m_hist;
        }

    }
}
