desc: FFT splitter

slider1:2<0,4,1{1024,2048,4096,8192}>FFT size
slider2:5000<0,20000,1>split freq
slider3:0<0,4,1{1/2,3/4,5/6,7/8}>low band dest
slider4:1<0,4,1{1/2,3/4,5/6,7/8}>high band dest
// slider5:0<0,1,0.1>debug

@init 

  fftsize = -1;
  pdc_bot_ch = 0;
  pdc_top_ch = 8;

  // array pointers
  window=0;
  buf1 = 16384;
  buf2 = 32768;
  splitLo1 = 49152;
  splitLo2 = 65536;
  splitHi1 = 81920;
  splitHi2 = 98304;

@slider

  pos = 0;
  memset(buf1, 0, 2*fftsize);
  memset(buf2, 0, 2*fftsize);
  memset(splitLo1, 0, 2*fftsize);
  memset(splitLo2, 0, 2*fftsize);
  memset(splitHi1, 0, 2*fftsize);
  memset(splitHi2, 0, 2*fftsize);

  sliderfft = (2^(slider1+10))|0;
  fftsize != sliderfft ? (
    memset(window, 0, fftsize); 
    fftsize = sliderfft;
    w = 2.0*3.14159/fftsize;
    i = 0;
    loop(fftsize/2,
      window[i] = 0.42-0.50*cos(i*w)+0.08*cos(2.0*i*w);
      i += 1;
    ); 
    pdc_delay = fftsize;
  );  

  splitfreq = 2*((fftsize * slider2 / srate)|0);
  wLo_01 = (slider3 == 0 ? 1.0 : 0.0);
  wLo_23 = (slider3 == 1 ? 1.0 : 0.0);
  wLo_45 = (slider3 == 2 ? 1.0 : 0.0);
  wLo_67 = (slider3 == 3 ? 1.0 : 0.0);
  wHi_01 = (slider4 == 0 ? 1.0 : 0.0);
  wHi_23 = (slider4 == 1 ? 1.0 : 0.0);
  wHi_45 = (slider4 == 2 ? 1.0 : 0.0);
  wHi_67 = (slider4 == 3 ? 1.0 : 0.0);

@sample

  pos >= fftsize ? (
    //memcpy(buf1, buf2+fftsize, fftsize);
    tmp = buf1;
    buf1 = buf2;
    buf2 = tmp;
 
    tmp = splitLo1;
    splitLo1 = splitLo2;
    splitLo2 = tmp;

    tmp = splitHi1;
    splitHi1 = splitHi2;
    splitHi2 = tmp;    
    
    fft(buf1, fftsize);
    fft_permute(buf1, fftsize);
 
    memcpy(splitLo1+2, buf1+2, splitfreq);
    memset(splitLo1+splitfreq+2, 0, 2*(fftsize-splitfreq-1));
    memcpy(splitLo1+2*fftsize-splitfreq, buf1+2*fftsize-splitfreq, splitfreq);

    i = 0;
    sumRe = sumIm = 0.0;
    loop(splitfreq/2,
      sumRe += splitLo1[i+2] + splitLo1[2*fftsize-i-2];
      sumIm += splitLo1[i+3] + splitLo1[2*fftsize-i-1];
      i += 2;
    );
    splitLo1[0] = -sumRe;
    splitLo1[1] = -sumIm;

    memset(splitHi1, 0, splitfreq+2);
    memcpy(splitHi1+splitfreq+2, buf1+splitfreq+2, 2*(fftsize-splitfreq-1));
    memset(splitHi1+2*fftsize-splitfreq, 0, splitfreq);  

    i = splitfreq+2;
    sumRe = sumIm = 0.0;
    loop(fftsize-splitfreq-1,
      sumRe += splitHi1[i];
      sumIm += splitHi1[i+1];
      i += 2;
    );
    splitHi1[0] = -sumRe;
    splitHi1[1] = -sumIm;

    fft_ipermute(splitLo1, fftsize);
    fft_ipermute(splitHi1, fftsize);
    ifft(splitLo1, fftsize);
    ifft(splitHi1, fftsize);

    pos=0;
  );

  w1 = window[pos/2];
  w2 = window[(fftsize-pos)/2-1];
  sw = (w1+w2)*fftsize;

  buf1[pos] = w1*spl0;
  buf1[pos+1] = w1*spl1;
  buf2[fftsize+pos] = w2*spl0;
  buf2[fftsize+pos+1] = w2*spl1;

  spl0Lo = (splitLo1[pos]+splitLo2[fftsize+pos])/sw;
  spl1Lo = (splitLo1[pos+1]+splitLo2[fftsize+pos+1])/sw;
  
  spl0Hi = (splitHi1[pos]+splitHi2[fftsize+pos])/sw;
  spl1Hi = (splitHi1[pos+1]+splitHi2[fftsize+pos+1])/sw;
  
  spl0 = wLo_01*spl0Lo + wHi_01*spl0Hi;
  spl1 = wLo_01*spl1Lo + wHi_01*spl1Hi;
  spl2 = wLo_23*spl0Lo + wHi_23*spl0Hi;
  spl3 = wLo_23*spl1Lo + wHi_23*spl1Hi;
  spl4 = wLo_45*spl0Lo + wHi_45*spl0Hi;
  spl5 = wLo_45*spl1Lo + wHi_45*spl1Hi;
  spl6 = wLo_67*spl0Lo + wHi_67*spl0Hi;
  spl7 = wLo_67*spl1Lo + wHi_67*spl1Hi;

  pos += 2;


