#define X0 0
#define Y0 1
#define X1 2
#define Y1 3
#define X2 4
#define Y2 5

#define X 0
#define Y 1
#define Z 2
#define W 3

#define MINAREA 1.0e-5

typedef float POINT[4];

static int CalcDeltas2 ( POINT *s, int i, float *d)
{
  float recip, temp, cc;

  d[X0] = s[0][X];
  d[Y0] = s[0][Y];
  d[X1] = s[i][X] - s[0][X];
  d[Y1] = s[i][Y] - s[0][Y];
  d[X2] = s[i+1][X] - s[0][X];
  d[Y2] = s[i+1][Y] - s[0][Y];
  cc = d[X1]*d[Y2] - d[Y1]*d[X2];
  temp = cc;
  if (cc < 0)
    temp = -cc;
  if (temp < MINAREA) return -1;                /* is polygon degenerate ? */
    recip = 1.0f/cc;
  d[X1] *= recip;
  d[Y1] *= recip;
  d[X2] *= recip;
  d[Y2] *= recip;
  return(0);
}

#define FitPlane(A, B, C, d,x0,x1,x2)   \
{                                       \
   dz1 = (x1) - (x0);                    \
  dz2 = (x2) - (x0);                    \
  A = d[Y2]*dz1 - d[Y1]*dz2;           \
  B = d[X1]*dz2 - d[X2]*dz1;           \
  C = (x0) - A * d[X0] - B * d[Y0];  \
}

static void test ( float *coeff )
{
  register float A, B, C, dz1, dz2;
  POINT tri[3];
  float deltas[6];

  CalcDeltas2 ( tri, 1, deltas );

  FitPlane ( A, B, C, deltas, tri[0][Z], tri[1][Z], tri[2][Z] );
  *coeff++=A;
  *coeff++=B;
  *coeff++=C;

  FitPlane ( A, B, C, deltas, tri[0][W], tri[1][W], tri[2][W] );
  *coeff++=A;
  *coeff++=B;
  *coeff++=C;


}