float CLASS find_green (int bps, int bite, int off0, int off1)
{
  UINT64 bitbuf=0;
  int vbits, col, i, c;
  ushort img[2][2064];
  double sum[] = {0, 0};
  if(width > 2064) return 0.f; // too wide

  FORC(2) {
    fseek (ifp, c ? off1:off0, SEEK_SET);
    for (vbits=col=0; col < width; col++) {
      for (vbits -= bps; vbits < 0; vbits += bite) {
	bitbuf <<= bite;
	for (i=0; i < bite; i+=8)
	  bitbuf |= (unsigned) (fgetc(ifp) << i);
      }
      img[c][col] = bitbuf << (64-bps-vbits) >> (64-bps);
    }
  }
  FORC(width-1) {
    sum[ c & 1] += ABS(img[0][c]-img[1][c+1]);
    sum[~c & 1] += ABS(img[1][c]-img[0][c+1]);
  }
  return 100 * log(sum[0]/sum[1]);
}
float CLASS find_green (int bps, int bite, int off0, int off1)
{
  UINT64 bitbuf=0;
  int vbits, col, i, c;
  ushort img[2][2064];
  double sum[] = {0, 0};
  if(width > 2064) return 0.f;  

  FORC(2) {
    fseek (ifp, c ? off1:off0, SEEK_SET);
    for (vbits=col=0; col < width; col++) {
      for (vbits -= bps; vbits < 0; vbits += bite) {
	bitbuf <<= bite;
	for (i=0; i < bite; i+=8)
	  bitbuf |= (unsigned) (fgetc(ifp) << i);
      }
      img[c][col] = bitbuf << (64-bps-vbits) >> (64-bps);
    }
  }
  FORC(width-1) {
    sum[ c & 1] += ABS(img[0][c]-img[1][c+1]);
    sum[~c & 1] += ABS(img[1][c]-img[0][c+1]);
  }
  return 100 * log(sum[0]/sum[1]);
}