pprz_algebra_float.c

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/*
 * Copyright (C) 2008-2014 The Paparazzi Team
 *
 * This file is part of paparazzi.
 *
 * paparazzi is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * paparazzi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with paparazzi; see the file COPYING.  If not, see
 * <http://www.gnu.org/licenses/>.
 */

#include "pprz_algebra_float.h"

void float_vect3_integrate_fi(struct FloatVect3 *vec, struct FloatVect3 *dv, float dt)
{
  vec->x += dv->x * dt;
  vec->y += dv->y * dt;
  vec->z += dv->z * dt;
}

void float_rates_integrate_fi(struct FloatRates *r, struct FloatRates *dr, float dt)
{
  r->p += dr->p * dt;
  r->q += dr->q * dt;
  r->r += dr->r * dt;
}

void float_rates_of_euler_dot(struct FloatRates *r, struct FloatEulers *e, struct FloatEulers *edot)
{
  r->p = edot->phi                             -                sinf(e->theta) * edot->psi;
  r->q =            cosf(e->phi) * edot->theta + sinf(e->phi) * cosf(e->theta) * edot->psi;
  r->r =           -sinf(e->phi) * edot->theta + cosf(e->phi) * cosf(e->theta) * edot->psi;
}




void float_rmat_inv(struct FloatRMat *m_b2a, struct FloatRMat *m_a2b)
{
  RMAT_ELMT(*m_b2a, 0, 0) = RMAT_ELMT(*m_a2b, 0, 0);
  RMAT_ELMT(*m_b2a, 0, 1) = RMAT_ELMT(*m_a2b, 1, 0);
  RMAT_ELMT(*m_b2a, 0, 2) = RMAT_ELMT(*m_a2b, 2, 0);
  RMAT_ELMT(*m_b2a, 1, 0) = RMAT_ELMT(*m_a2b, 0, 1);
  RMAT_ELMT(*m_b2a, 1, 1) = RMAT_ELMT(*m_a2b, 1, 1);
  RMAT_ELMT(*m_b2a, 1, 2) = RMAT_ELMT(*m_a2b, 2, 1);
  RMAT_ELMT(*m_b2a, 2, 0) = RMAT_ELMT(*m_a2b, 0, 2);
  RMAT_ELMT(*m_b2a, 2, 1) = RMAT_ELMT(*m_a2b, 1, 2);
  RMAT_ELMT(*m_b2a, 2, 2) = RMAT_ELMT(*m_a2b, 2, 2);
}

float float_rmat_norm(struct FloatRMat *rm)
{
  return sqrtf(SQUARE(rm->m[0]) + SQUARE(rm->m[1]) + SQUARE(rm->m[2]) +
               SQUARE(rm->m[3]) + SQUARE(rm->m[4]) + SQUARE(rm->m[5]) +
               SQUARE(rm->m[6]) + SQUARE(rm->m[7]) + SQUARE(rm->m[8]));
}

void float_rmat_comp(struct FloatRMat *m_a2c, struct FloatRMat *m_a2b, struct FloatRMat *m_b2c)
{
  m_a2c->m[0] = m_b2c->m[0] * m_a2b->m[0] + m_b2c->m[1] * m_a2b->m[3] + m_b2c->m[2] * m_a2b->m[6];
  m_a2c->m[1] = m_b2c->m[0] * m_a2b->m[1] + m_b2c->m[1] * m_a2b->m[4] + m_b2c->m[2] * m_a2b->m[7];
  m_a2c->m[2] = m_b2c->m[0] * m_a2b->m[2] + m_b2c->m[1] * m_a2b->m[5] + m_b2c->m[2] * m_a2b->m[8];
  m_a2c->m[3] = m_b2c->m[3] * m_a2b->m[0] + m_b2c->m[4] * m_a2b->m[3] + m_b2c->m[5] * m_a2b->m[6];
  m_a2c->m[4] = m_b2c->m[3] * m_a2b->m[1] + m_b2c->m[4] * m_a2b->m[4] + m_b2c->m[5] * m_a2b->m[7];
  m_a2c->m[5] = m_b2c->m[3] * m_a2b->m[2] + m_b2c->m[4] * m_a2b->m[5] + m_b2c->m[5] * m_a2b->m[8];
  m_a2c->m[6] = m_b2c->m[6] * m_a2b->m[0] + m_b2c->m[7] * m_a2b->m[3] + m_b2c->m[8] * m_a2b->m[6];
  m_a2c->m[7] = m_b2c->m[6] * m_a2b->m[1] + m_b2c->m[7] * m_a2b->m[4] + m_b2c->m[8] * m_a2b->m[7];
  m_a2c->m[8] = m_b2c->m[6] * m_a2b->m[2] + m_b2c->m[7] * m_a2b->m[5] + m_b2c->m[8] * m_a2b->m[8];
}

void float_rmat_comp_inv(struct FloatRMat *m_a2b, struct FloatRMat *m_a2c, struct FloatRMat *m_b2c)
{
  m_a2b->m[0] = m_b2c->m[0] * m_a2c->m[0] + m_b2c->m[3] * m_a2c->m[3] + m_b2c->m[6] * m_a2c->m[6];
  m_a2b->m[1] = m_b2c->m[0] * m_a2c->m[1] + m_b2c->m[3] * m_a2c->m[4] + m_b2c->m[6] * m_a2c->m[7];
  m_a2b->m[2] = m_b2c->m[0] * m_a2c->m[2] + m_b2c->m[3] * m_a2c->m[5] + m_b2c->m[6] * m_a2c->m[8];
  m_a2b->m[3] = m_b2c->m[1] * m_a2c->m[0] + m_b2c->m[4] * m_a2c->m[3] + m_b2c->m[7] * m_a2c->m[6];
  m_a2b->m[4] = m_b2c->m[1] * m_a2c->m[1] + m_b2c->m[4] * m_a2c->m[4] + m_b2c->m[7] * m_a2c->m[7];
  m_a2b->m[5] = m_b2c->m[1] * m_a2c->m[2] + m_b2c->m[4] * m_a2c->m[5] + m_b2c->m[7] * m_a2c->m[8];
  m_a2b->m[6] = m_b2c->m[2] * m_a2c->m[0] + m_b2c->m[5] * m_a2c->m[3] + m_b2c->m[8] * m_a2c->m[6];
  m_a2b->m[7] = m_b2c->m[2] * m_a2c->m[1] + m_b2c->m[5] * m_a2c->m[4] + m_b2c->m[8] * m_a2c->m[7];
  m_a2b->m[8] = m_b2c->m[2] * m_a2c->m[2] + m_b2c->m[5] * m_a2c->m[5] + m_b2c->m[8] * m_a2c->m[8];
}

void float_rmat_vmult(struct FloatVect3 *vb, struct FloatRMat *m_a2b, struct FloatVect3 *va)
{
  vb->x = m_a2b->m[0] * va->x + m_a2b->m[1] * va->y + m_a2b->m[2] * va->z;
  vb->y = m_a2b->m[3] * va->x + m_a2b->m[4] * va->y + m_a2b->m[5] * va->z;
  vb->z = m_a2b->m[6] * va->x + m_a2b->m[7] * va->y + m_a2b->m[8] * va->z;
}

void float_rmat_transp_vmult(struct FloatVect3 *vb, struct FloatRMat *m_b2a, struct FloatVect3 *va)
{
  vb->x = m_b2a->m[0] * va->x + m_b2a->m[3] * va->y + m_b2a->m[6] * va->z;
  vb->y = m_b2a->m[1] * va->x + m_b2a->m[4] * va->y + m_b2a->m[7] * va->z;
  vb->z = m_b2a->m[2] * va->x + m_b2a->m[5] * va->y + m_b2a->m[8] * va->z;
}

void float_rmat_mult(struct FloatEulers *rb, struct FloatRMat *m_a2b, struct FloatEulers *ra)
{
  rb->phi = m_a2b->m[0] * ra->phi + m_a2b->m[1] * ra->theta + m_a2b->m[2] * ra->psi;
  rb->theta = m_a2b->m[3] * ra->phi + m_a2b->m[4] * ra->theta + m_a2b->m[5] * ra->psi;
  rb->psi = m_a2b->m[6] * ra->phi + m_a2b->m[7] * ra->theta + m_a2b->m[8] * ra->psi;
}

void float_rmat_transp_mult(struct FloatEulers *rb, struct FloatRMat *m_b2a, struct FloatEulers *ra)
{
  rb->phi = m_b2a->m[0] * ra->phi + m_b2a->m[3] * ra->theta + m_b2a->m[6] * ra->psi;
  rb->theta = m_b2a->m[1] * ra->phi + m_b2a->m[4] * ra->theta + m_b2a->m[7] * ra->psi;
  rb->psi = m_b2a->m[2] * ra->phi + m_b2a->m[5] * ra->theta + m_b2a->m[8] * ra->psi;
}

void float_rmat_ratemult(struct FloatRates *rb, struct FloatRMat *m_a2b, struct FloatRates *ra)
{
  rb->p = m_a2b->m[0] * ra->p + m_a2b->m[1] * ra->q + m_a2b->m[2] * ra->r;
  rb->q = m_a2b->m[3] * ra->p + m_a2b->m[4] * ra->q + m_a2b->m[5] * ra->r;
  rb->r = m_a2b->m[6] * ra->p + m_a2b->m[7] * ra->q + m_a2b->m[8] * ra->r;
}

void float_rmat_transp_ratemult(struct FloatRates *rb, struct FloatRMat *m_b2a, struct FloatRates *ra)
{
  rb->p = m_b2a->m[0] * ra->p + m_b2a->m[3] * ra->q + m_b2a->m[6] * ra->r;
  rb->q = m_b2a->m[1] * ra->p + m_b2a->m[4] * ra->q + m_b2a->m[7] * ra->r;
  rb->r = m_b2a->m[2] * ra->p + m_b2a->m[5] * ra->q + m_b2a->m[8] * ra->r;
}


void float_rmat_of_axis_angle(struct FloatRMat *rm, struct FloatVect3 *uv, float angle)
{
  const float ux2  = uv->x * uv->x;
  const float uy2  = uv->y * uv->y;
  const float uz2  = uv->z * uv->z;
  const float uxuy = uv->x * uv->y;
  const float uyuz = uv->y * uv->z;
  const float uxuz = uv->x * uv->z;
  const float can  = cosf(angle);
  const float san  = sinf(angle);
  const float one_m_can = (1. - can);

  RMAT_ELMT(*rm, 0, 0) = ux2 + (1. - ux2) * can;
  RMAT_ELMT(*rm, 0, 1) = uxuy * one_m_can + uv->z * san;
  RMAT_ELMT(*rm, 0, 2) = uxuz * one_m_can - uv->y * san;
  RMAT_ELMT(*rm, 1, 0) = RMAT_ELMT(*rm, 0, 1);
  RMAT_ELMT(*rm, 1, 1) = uy2 + (1. - uy2) * can;
  RMAT_ELMT(*rm, 1, 2) = uyuz * one_m_can + uv->x * san;
  RMAT_ELMT(*rm, 2, 0) = RMAT_ELMT(*rm, 0, 2);
  RMAT_ELMT(*rm, 2, 1) = RMAT_ELMT(*rm, 1, 2);
  RMAT_ELMT(*rm, 2, 2) = uz2 + (1. - uz2) * can;
}


/* C n->b rotation matrix */
void float_rmat_of_eulers_321(struct FloatRMat *rm, struct FloatEulers *e)
{
  const float sphi   = sinf(e->phi);
  const float cphi   = cosf(e->phi);
  const float stheta = sinf(e->theta);
  const float ctheta = cosf(e->theta);
  const float spsi   = sinf(e->psi);
  const float cpsi   = cosf(e->psi);

  RMAT_ELMT(*rm, 0, 0) = ctheta * cpsi;
  RMAT_ELMT(*rm, 0, 1) = ctheta * spsi;
  RMAT_ELMT(*rm, 0, 2) = -stheta;
  RMAT_ELMT(*rm, 1, 0) = sphi * stheta * cpsi - cphi * spsi;
  RMAT_ELMT(*rm, 1, 1) = sphi * stheta * spsi + cphi * cpsi;
  RMAT_ELMT(*rm, 1, 2) = sphi * ctheta;
  RMAT_ELMT(*rm, 2, 0) = cphi * stheta * cpsi + sphi * spsi;
  RMAT_ELMT(*rm, 2, 1) = cphi * stheta * spsi - sphi * cpsi;
  RMAT_ELMT(*rm, 2, 2) = cphi * ctheta;
}

void float_rmat_of_eulers_312(struct FloatRMat *rm, struct FloatEulers *e)
{
  const float sphi   = sinf(e->phi);
  const float cphi   = cosf(e->phi);
  const float stheta = sinf(e->theta);
  const float ctheta = cosf(e->theta);
  const float spsi   = sinf(e->psi);
  const float cpsi   = cosf(e->psi);

  RMAT_ELMT(*rm, 0, 0) =  ctheta * cpsi - sphi * stheta * spsi;
  RMAT_ELMT(*rm, 0, 1) =  ctheta * spsi + sphi * stheta * cpsi;
  RMAT_ELMT(*rm, 0, 2) = -cphi * stheta;
  RMAT_ELMT(*rm, 1, 0) = -cphi * spsi;
  RMAT_ELMT(*rm, 1, 1) =  cphi * cpsi;
  RMAT_ELMT(*rm, 1, 2) =  sphi;
  RMAT_ELMT(*rm, 2, 0) =  stheta * cpsi + sphi * ctheta * spsi;
  RMAT_ELMT(*rm, 2, 1) =  stheta * spsi - sphi * ctheta * cpsi;
  RMAT_ELMT(*rm, 2, 2) =  cphi * ctheta;
}


/* C n->b rotation matrix */
void float_rmat_of_quat(struct FloatRMat *rm, struct FloatQuat *q)
{
  const float _a = M_SQRT2 * q->qi;
  const float _b = M_SQRT2 * q->qx;
  const float _c = M_SQRT2 * q->qy;
  const float _d = M_SQRT2 * q->qz;
  const float a2_1 = _a * _a - 1;
  const float ab = _a * _b;
  const float ac = _a * _c;
  const float ad = _a * _d;
  const float bc = _b * _c;
  const float bd = _b * _d;
  const float cd = _c * _d;
  RMAT_ELMT(*rm, 0, 0) = a2_1 + _b * _b;
  RMAT_ELMT(*rm, 0, 1) = bc + ad;
  RMAT_ELMT(*rm, 0, 2) = bd - ac;
  RMAT_ELMT(*rm, 1, 0) = bc - ad;
  RMAT_ELMT(*rm, 1, 1) = a2_1 + _c * _c;
  RMAT_ELMT(*rm, 1, 2) = cd + ab;
  RMAT_ELMT(*rm, 2, 0) = bd + ac;
  RMAT_ELMT(*rm, 2, 1) = cd - ab;
  RMAT_ELMT(*rm, 2, 2) = a2_1 + _d * _d;
}

void float_rmat_integrate_fi(struct FloatRMat *rm, struct FloatRates *omega, float dt)
{
  struct FloatRMat exp_omega_dt = {
    {
      1.        ,  dt *omega->r, -dt *omega->q,
      -dt *omega->r,  1.        ,  dt *omega->p,
      dt *omega->q, -dt *omega->p,  1.
    }
  };
  struct FloatRMat R_tdt;
  float_rmat_comp(&R_tdt, rm, &exp_omega_dt);
  memcpy(rm, &R_tdt, sizeof(R_tdt));
}

static inline float renorm_factor(float n)
{
  if (n < 1.5625f && n > 0.64f) {
    return .5 * (3 - n);
  } else if (n < 100.0f && n > 0.01f) {
    return  1. / sqrtf(n);
  } else {
    return 0.;
  }
}

float float_rmat_reorthogonalize(struct FloatRMat *rm)
{
  const struct FloatVect3 r0 = {RMAT_ELMT(*rm, 0, 0),
          RMAT_ELMT(*rm, 0, 1),
          RMAT_ELMT(*rm, 0, 2)
  };
  const struct FloatVect3 r1 = {RMAT_ELMT(*rm, 1, 0),
          RMAT_ELMT(*rm, 1, 1),
          RMAT_ELMT(*rm, 1, 2)
  };
  float _err = -0.5 * VECT3_DOT_PRODUCT(r0, r1);
  struct FloatVect3 r0_t;
  VECT3_SUM_SCALED(r0_t, r0, r1, _err);
  struct FloatVect3 r1_t;
  VECT3_SUM_SCALED(r1_t,  r1, r0, _err);
  struct FloatVect3 r2_t;
  VECT3_CROSS_PRODUCT(r2_t, r0_t, r1_t);
  float s = renorm_factor(VECT3_NORM2(r0_t));
  MAT33_ROW_VECT3_SMUL(*rm, 0, r0_t, s);
  s = renorm_factor(VECT3_NORM2(r1_t));
  MAT33_ROW_VECT3_SMUL(*rm, 1, r1_t, s);
  s = renorm_factor(VECT3_NORM2(r2_t));
  MAT33_ROW_VECT3_SMUL(*rm, 2, r2_t, s);

  return _err;
}


/*
 *
 * Quaternion functions.
 *
 */

void float_quat_comp(struct FloatQuat *a2c, struct FloatQuat *a2b, struct FloatQuat *b2c)
{
  a2c->qi = a2b->qi * b2c->qi - a2b->qx * b2c->qx - a2b->qy * b2c->qy - a2b->qz * b2c->qz;
  a2c->qx = a2b->qi * b2c->qx + a2b->qx * b2c->qi + a2b->qy * b2c->qz - a2b->qz * b2c->qy;
  a2c->qy = a2b->qi * b2c->qy - a2b->qx * b2c->qz + a2b->qy * b2c->qi + a2b->qz * b2c->qx;
  a2c->qz = a2b->qi * b2c->qz + a2b->qx * b2c->qy - a2b->qy * b2c->qx + a2b->qz * b2c->qi;
}

void float_quat_comp_inv(struct FloatQuat *a2b, struct FloatQuat *a2c, struct FloatQuat *b2c)
{
  a2b->qi =  a2c->qi * b2c->qi + a2c->qx * b2c->qx + a2c->qy * b2c->qy + a2c->qz * b2c->qz;
  a2b->qx = -a2c->qi * b2c->qx + a2c->qx * b2c->qi - a2c->qy * b2c->qz + a2c->qz * b2c->qy;
  a2b->qy = -a2c->qi * b2c->qy + a2c->qx * b2c->qz + a2c->qy * b2c->qi - a2c->qz * b2c->qx;
  a2b->qz = -a2c->qi * b2c->qz - a2c->qx * b2c->qy + a2c->qy * b2c->qx + a2c->qz * b2c->qi;
}

void float_quat_inv_comp(struct FloatQuat *b2c, struct FloatQuat *a2b, struct FloatQuat *a2c)
{
  b2c->qi = a2b->qi * a2c->qi + a2b->qx * a2c->qx + a2b->qy * a2c->qy + a2b->qz * a2c->qz;
  b2c->qx = a2b->qi * a2c->qx - a2b->qx * a2c->qi - a2b->qy * a2c->qz + a2b->qz * a2c->qy;
  b2c->qy = a2b->qi * a2c->qy + a2b->qx * a2c->qz - a2b->qy * a2c->qi - a2b->qz * a2c->qx;
  b2c->qz = a2b->qi * a2c->qz - a2b->qx * a2c->qy + a2b->qy * a2c->qx - a2b->qz * a2c->qi;
}

void float_quat_comp_norm_shortest(struct FloatQuat *a2c, struct FloatQuat *a2b, struct FloatQuat *b2c)
{
  float_quat_comp(a2c, a2b, b2c);
  float_quat_wrap_shortest(a2c);
  float_quat_normalize(a2c);
}

void float_quat_comp_inv_norm_shortest(struct FloatQuat *a2b, struct FloatQuat *a2c, struct FloatQuat *b2c)
{
  float_quat_comp_inv(a2b, a2c, b2c);
  float_quat_wrap_shortest(a2b);
  float_quat_normalize(a2b);
}

void float_quat_inv_comp_norm_shortest(struct FloatQuat *b2c, struct FloatQuat *a2b, struct FloatQuat *a2c)
{
  float_quat_inv_comp(b2c, a2b, a2c);
  float_quat_wrap_shortest(b2c);
  float_quat_normalize(b2c);
}

void float_quat_differential(struct FloatQuat *q_out, struct FloatRates *w, float dt)
{
  const float v_norm = sqrtf(w->p * w->p + w->q * w->q + w->r * w->r);
  const float c2 = cos(dt * v_norm / 2.0);
  const float s2 = sin(dt * v_norm / 2.0);
  if (v_norm < 1e-8) {
    q_out->qi = 1;
    q_out->qx = 0;
    q_out->qy = 0;
    q_out->qz = 0;
  } else {
    q_out->qi = c2;
    q_out->qx = w->p / v_norm * s2;
    q_out->qy = w->q / v_norm * s2;
    q_out->qz = w->r / v_norm * s2;
  }
}

void float_quat_integrate_fi(struct FloatQuat *q, struct FloatRates *omega, float dt)
{
  const float qi = q->qi;
  const float qx = q->qx;
  const float qy = q->qy;
  const float qz = q->qz;
  const float dp = 0.5 * dt * omega->p;
  const float dq = 0.5 * dt * omega->q;
  const float dr = 0.5 * dt * omega->r;
  q->qi = qi    - dp * qx - dq * qy - dr * qz;
  q->qx = dp * qi +    qx + dr * qy - dq * qz;
  q->qy = dq * qi - dr * qx +    qy + dp * qz;
  q->qz = dr * qi + dq * qx - dp * qy +    qz;
}

void float_quat_integrate(struct FloatQuat *q, struct FloatRates *omega, float dt)
{
  const float no = FLOAT_RATES_NORM(*omega);
  if (no > FLT_MIN) {
    const float a  = 0.5 * no * dt;
    const float ca = cosf(a);
    const float sa_ov_no = sinf(a) / no;
    const float dp = sa_ov_no * omega->p;
    const float dq = sa_ov_no * omega->q;
    const float dr = sa_ov_no * omega->r;
    const float qi = q->qi;
    const float qx = q->qx;
    const float qy = q->qy;
    const float qz = q->qz;
    q->qi = ca * qi - dp * qx - dq * qy - dr * qz;
    q->qx = dp * qi + ca * qx + dr * qy - dq * qz;
    q->qy = dq * qi - dr * qx + ca * qy + dp * qz;
    q->qz = dr * qi + dq * qx - dp * qy + ca * qz;
  }
}

void float_quat_vmult(struct FloatVect3 *v_out, struct FloatQuat *q, const struct FloatVect3 *v_in)
{
  const float qi2_M1_2  = q->qi * q->qi - 0.5;
  const float qiqx = q->qi * q->qx;
  const float qiqy = q->qi * q->qy;
  const float qiqz = q->qi * q->qz;
  float m01  = q->qx * q->qy; /* aka qxqy */
  float m02  = q->qx * q->qz; /* aka qxqz */
  float m12  = q->qy * q->qz; /* aka qyqz */

  const float m00  = qi2_M1_2 + q->qx * q->qx;
  const float m10  = m01 - qiqz;
  const float m20  = m02 + qiqy;
  const float m21  = m12 - qiqx;
  m01 += qiqz;
  m02 -= qiqy;
  m12 += qiqx;
  const float m11  = qi2_M1_2 + q->qy * q->qy;
  const float m22  = qi2_M1_2 + q->qz * q->qz;
  v_out->x = 2 * (m00 * v_in->x + m01 * v_in->y + m02 * v_in->z);
  v_out->y = 2 * (m10 * v_in->x + m11 * v_in->y + m12 * v_in->z);
  v_out->z = 2 * (m20 * v_in->x + m21 * v_in->y + m22 * v_in->z);
}

void float_quat_derivative(struct FloatQuat *qd, struct FloatRates *r, struct FloatQuat *q)
{
  qd->qi = -0.5 * (r->p * q->qx + r->q * q->qy + r->r * q->qz);
  qd->qx = -0.5 * (-r->p * q->qi - r->r * q->qy + r->q * q->qz);
  qd->qy = -0.5 * (-r->q * q->qi + r->r * q->qx - r->p * q->qz);
  qd->qz = -0.5 * (-r->r * q->qi - r->q * q->qx + r->p * q->qy);
}

void float_quat_derivative_lagrange(struct FloatQuat *qd, struct FloatRates *r, struct FloatQuat *q)
{
  const float K_LAGRANGE = 1.;
  const float c = K_LAGRANGE * (1 - float_quat_norm(q)) / -0.5;
  qd->qi = -0.5 * (c * q->qi + r->p * q->qx + r->q * q->qy + r->r * q->qz);
  qd->qx = -0.5 * (-r->p * q->qi +      c * q->qx - r->r * q->qy + r->q * q->qz);
  qd->qy = -0.5 * (-r->q * q->qi + r->r * q->qx +      c * q->qy - r->p * q->qz);
  qd->qz = -0.5 * (-r->r * q->qi - r->q * q->qx + r->p * q->qy +      c * q->qz);
}

void float_quat_of_eulers(struct FloatQuat *q, struct FloatEulers *e)
{

  const float phi2   = e->phi / 2.0;
  const float theta2 = e->theta / 2.0;
  const float psi2   = e->psi / 2.0;

  const float s_phi2   = sinf(phi2);
  const float c_phi2   = cosf(phi2);
  const float s_theta2 = sinf(theta2);
  const float c_theta2 = cosf(theta2);
  const float s_psi2   = sinf(psi2);
  const float c_psi2   = cosf(psi2);

  q->qi =  c_phi2 * c_theta2 * c_psi2 + s_phi2 * s_theta2 * s_psi2;
  q->qx = -c_phi2 * s_theta2 * s_psi2 + s_phi2 * c_theta2 * c_psi2;
  q->qy =  c_phi2 * s_theta2 * c_psi2 + s_phi2 * c_theta2 * s_psi2;
  q->qz =  c_phi2 * c_theta2 * s_psi2 - s_phi2 * s_theta2 * c_psi2;
}

void float_quat_of_axis_angle(struct FloatQuat *q, const struct FloatVect3 *uv, float angle)
{
  const float san = sinf(angle / 2.);
  q->qi = cosf(angle / 2.);
  q->qx = san * uv->x;
  q->qy = san * uv->y;
  q->qz = san * uv->z;
}

void float_quat_of_orientation_vect(struct FloatQuat *q, const struct FloatVect3 *ov)
{
  const float ov_norm = sqrtf(ov->x * ov->x + ov->y * ov->y + ov->z * ov->z);
  if (ov_norm < 1e-8) {
    q->qi = 1;
    q->qx = 0;
    q->qy = 0;
    q->qz = 0;
  } else {
    const float s2_normalized = sinf(ov_norm / 2.0) / ov_norm;
    q->qi = cosf(ov_norm / 2.0);
    q->qx = ov->x * s2_normalized;
    q->qy = ov->y * s2_normalized;
    q->qz = ov->z * s2_normalized;
  }
}

void float_quat_of_rmat(struct FloatQuat *q, struct FloatRMat *rm)
{
  const float tr = RMAT_TRACE(*rm);
  if (tr > 0) {
    const float two_qi = sqrtf(1. + tr);
    const float four_qi = 2. * two_qi;
    q->qi = 0.5 * two_qi;
    q->qx = (RMAT_ELMT(*rm, 1, 2) - RMAT_ELMT(*rm, 2, 1)) / four_qi;
    q->qy = (RMAT_ELMT(*rm, 2, 0) - RMAT_ELMT(*rm, 0, 2)) / four_qi;
    q->qz = (RMAT_ELMT(*rm, 0, 1) - RMAT_ELMT(*rm, 1, 0)) / four_qi;
    /*printf("tr > 0\n");*/
  } else {
    if (RMAT_ELMT(*rm, 0, 0) > RMAT_ELMT(*rm, 1, 1) &&
        RMAT_ELMT(*rm, 0, 0) > RMAT_ELMT(*rm, 2, 2)) {
      const float two_qx = sqrtf(RMAT_ELMT(*rm, 0, 0) - RMAT_ELMT(*rm, 1, 1)
                                 - RMAT_ELMT(*rm, 2, 2) + 1);
      const float four_qx = 2. * two_qx;
      q->qi = (RMAT_ELMT(*rm, 1, 2) - RMAT_ELMT(*rm, 2, 1)) / four_qx;
      q->qx = 0.5 * two_qx;
      q->qy = (RMAT_ELMT(*rm, 0, 1) + RMAT_ELMT(*rm, 1, 0)) / four_qx;
      q->qz = (RMAT_ELMT(*rm, 2, 0) + RMAT_ELMT(*rm, 0, 2)) / four_qx;
      /*printf("m00 largest\n");*/
    } else if (RMAT_ELMT(*rm, 1, 1) > RMAT_ELMT(*rm, 2, 2)) {
      const float two_qy =
        sqrtf(RMAT_ELMT(*rm, 1, 1) - RMAT_ELMT(*rm, 0, 0) - RMAT_ELMT(*rm, 2, 2) + 1);
      const float four_qy = 2. * two_qy;
      q->qi = (RMAT_ELMT(*rm, 2, 0) - RMAT_ELMT(*rm, 0, 2)) / four_qy;
      q->qx = (RMAT_ELMT(*rm, 0, 1) + RMAT_ELMT(*rm, 1, 0)) / four_qy;
      q->qy = 0.5 * two_qy;
      q->qz = (RMAT_ELMT(*rm, 1, 2) + RMAT_ELMT(*rm, 2, 1)) / four_qy;
      /*printf("m11 largest\n");*/
    } else {
      const float two_qz =
        sqrtf(RMAT_ELMT(*rm, 2, 2) - RMAT_ELMT(*rm, 0, 0) - RMAT_ELMT(*rm, 1, 1) + 1);
      const float four_qz = 2. * two_qz;
      q->qi = (RMAT_ELMT(*rm, 0, 1) - RMAT_ELMT(*rm, 1, 0)) / four_qz;
      q->qx = (RMAT_ELMT(*rm, 2, 0) + RMAT_ELMT(*rm, 0, 2)) / four_qz;
      q->qy = (RMAT_ELMT(*rm, 1, 2) + RMAT_ELMT(*rm, 2, 1)) / four_qz;
      q->qz = 0.5 * two_qz;
      /*printf("m22 largest\n");*/
    }
  }
}


/*
 *
 * Euler angle functions.
 *
 */

void float_eulers_of_rmat(struct FloatEulers *e, struct FloatRMat *rm)
{
  const float dcm00 = rm->m[0];
  const float dcm01 = rm->m[1];
  const float dcm02 = rm->m[2];
  const float dcm12 = rm->m[5];
  const float dcm22 = rm->m[8];
  e->phi   = atan2f(dcm12, dcm22);
  e->theta = -asinf(dcm02);
  e->psi   = atan2f(dcm01, dcm00);
}

void float_eulers_of_quat(struct FloatEulers *e, struct FloatQuat *q)
{
  const float qx2  = q->qx * q->qx;
  const float qy2  = q->qy * q->qy;
  const float qz2  = q->qz * q->qz;
  const float qiqx = q->qi * q->qx;
  const float qiqy = q->qi * q->qy;
  const float qiqz = q->qi * q->qz;
  const float qxqy = q->qx * q->qy;
  const float qxqz = q->qx * q->qz;
  const float qyqz = q->qy * q->qz;
  const float dcm00 = 1.0 - 2.*(qy2 +  qz2);
  const float dcm01 =       2.*(qxqy + qiqz);
  const float dcm02 =       2.*(qxqz - qiqy);
  const float dcm12 =       2.*(qyqz + qiqx);
  const float dcm22 = 1.0 - 2.*(qx2 +  qy2);

  e->phi = atan2f(dcm12, dcm22);
  e->theta = -asinf(dcm02);
  e->psi = atan2f(dcm01, dcm00);
}

/*
 * 4x4 Matrix inverse.
 * obtained from: http://rodolphe-vaillant.fr/?e=7
 */
float float_mat_minor_4d(float m[16], int r0, int r1, int r2, int c0, int c1, int c2);
void float_mat_adjoint_4d(float m[16], float adjOut[16]);
float float_mat_det_4d(float m[16]);

float float_mat_minor_4d(float m[16], int r0, int r1, int r2, int c0, int c1, int c2)
{
    return m[4*r0+c0] * (m[4*r1+c1] * m[4*r2+c2] - m[4*r2+c1] * m[4*r1+c2]) -
           m[4*r0+c1] * (m[4*r1+c0] * m[4*r2+c2] - m[4*r2+c0] * m[4*r1+c2]) +
           m[4*r0+c2] * (m[4*r1+c0] * m[4*r2+c1] - m[4*r2+c0] * m[4*r1+c1]);
}


void float_mat_adjoint_4d(float m[16], float adjOut[16])
{
  adjOut[ 0] =  float_mat_minor_4d(m,1,2,3,1,2,3);
  adjOut[ 1] = -float_mat_minor_4d(m,0,2,3,1,2,3);
  adjOut[ 2] =  float_mat_minor_4d(m,0,1,3,1,2,3);
  adjOut[ 3] = -float_mat_minor_4d(m,0,1,2,1,2,3);
  adjOut[ 4] = -float_mat_minor_4d(m,1,2,3,0,2,3);
  adjOut[ 5] =  float_mat_minor_4d(m,0,2,3,0,2,3);
  adjOut[ 6] = -float_mat_minor_4d(m,0,1,3,0,2,3);
  adjOut[ 7] =  float_mat_minor_4d(m,0,1,2,0,2,3);
  adjOut[ 8] =  float_mat_minor_4d(m,1,2,3,0,1,3);
  adjOut[ 9] = -float_mat_minor_4d(m,0,2,3,0,1,3);
  adjOut[10] =  float_mat_minor_4d(m,0,1,3,0,1,3);
  adjOut[11] = -float_mat_minor_4d(m,0,1,2,0,1,3);
  adjOut[12] = -float_mat_minor_4d(m,1,2,3,0,1,2);
  adjOut[13] =  float_mat_minor_4d(m,0,2,3,0,1,2);
  adjOut[14] = -float_mat_minor_4d(m,0,1,3,0,1,2);
  adjOut[15] =  float_mat_minor_4d(m,0,1,2,0,1,2);
}

float float_mat_det_4d(float m[16])
{
    return m[0] * float_mat_minor_4d(m, 1, 2, 3, 1, 2, 3) -
           m[1] * float_mat_minor_4d(m, 1, 2, 3, 0, 2, 3) +
           m[2] * float_mat_minor_4d(m, 1, 2, 3, 0, 1, 3) -
           m[3] * float_mat_minor_4d(m, 1, 2, 3, 0, 1, 2);
}

void float_mat_inv_4d(float invOut[16], float mat_in[16])
{
    float_mat_adjoint_4d(mat_in, invOut);

    float inv_det = 1.0f / float_mat_det_4d(mat_in);
    int i;
    for(i = 0; i < 16; ++i)
        invOut[i] = invOut[i] * inv_det;
}