
   /******************************************************************

       iLBC Speech Coder ANSI-C Source Code

       lsf.c

       Copyright (C) The Internet Society (2004).
       All Rights Reserved.

   ******************************************************************/

#include <string.h>





#include <math.h>

#include "iLBC_define.h"

   /*----------------------------------------------------------------*
    *  conversion from lpc coefficients to lsf coefficients
    *---------------------------------------------------------------*/

void a2lsf(float *freq,         /* (o) lsf coefficients */
  float *a                      /* (i) lpc coefficients */
  )
{
  float steps[LSF_NUMBER_OF_STEPS] =
    { (float) 0.00635, (float) 0.003175, (float) 0.0015875,
    (float) 0.00079375
  };
  float step;
  int step_idx;
  int lsp_index;
  float p[LPC_HALFORDER];
  float q[LPC_HALFORDER];
  float p_pre[LPC_HALFORDER];
  float q_pre[LPC_HALFORDER];
  float old_p, old_q, *old;
  float *pq_coef;
  float omega, old_omega;
  int i;
  float hlp, hlp1, hlp2, hlp3, hlp4, hlp5;

  for (i = 0; i < LPC_HALFORDER; i++) {
    p[i] = (float) -1.0 * (a[i + 1] + a[LPC_FILTERORDER - i]);
    q[i] = a[LPC_FILTERORDER - i] - a[i + 1];
  }

  p_pre[0] = (float) -1.0 - p[0];
  p_pre[1] = -p_pre[0] - p[1];
  p_pre[2] = -p_pre[1] - p[2];
  p_pre[3] = -p_pre[2] - p[3];
  p_pre[4] = -p_pre[3] - p[4];
  p_pre[4] = p_pre[4] / 2;

  q_pre[0] = (float) 1.0 - q[0];
  q_pre[1] = q_pre[0] - q[1];
  q_pre[2] = q_pre[1] - q[2];
  q_pre[3] = q_pre[2] - q[3];
  q_pre[4] = q_pre[3] - q[4];
  q_pre[4] = q_pre[4] / 2;

  omega = 0.0;





  old_omega = 0.0;

  old_p = FLOAT_MAX;
  old_q = FLOAT_MAX;

  /* Here we loop through lsp_index to find all the
     LPC_FILTERORDER roots for omega. */

  for (lsp_index = 0; lsp_index < LPC_FILTERORDER; lsp_index++) {

    /* Depending on lsp_index being even or odd, we
       alternatively solve the roots for the two LSP equations. */


    if ((lsp_index & 0x1) == 0) {
      pq_coef = p_pre;
      old = &old_p;
    } else {
      pq_coef = q_pre;
      old = &old_q;
    }

    /* Start with low resolution grid */

    for (step_idx = 0, step = steps[step_idx];
      step_idx < LSF_NUMBER_OF_STEPS;) {

      /*  cos(10piw) + pq(0)cos(8piw) + pq(1)cos(6piw) +
         pq(2)cos(4piw) + pq(3)cod(2piw) + pq(4) */

      hlp = (float) cos(omega * TWO_PI);
      hlp1 = (float) 2.0 *hlp + pq_coef[0];
      hlp2 = (float) 2.0 *hlp * hlp1 - (float) 1.0 + pq_coef[1];
      hlp3 = (float) 2.0 *hlp * hlp2 - hlp1 + pq_coef[2];
      hlp4 = (float) 2.0 *hlp * hlp3 - hlp2 + pq_coef[3];
      hlp5 = hlp * hlp4 - hlp3 + pq_coef[4];


      if (((hlp5 * (*old)) <= 0.0) || (omega >= 0.5)) {

        if (step_idx == (LSF_NUMBER_OF_STEPS - 1)) {

          if (fabs(hlp5) >= fabs(*old)) {
            freq[lsp_index] = omega - step;
          } else {
            freq[lsp_index] = omega;
          }







          if ((*old) >= 0.0) {
            *old = (float) -1.0 * FLOAT_MAX;
          } else {
            *old = FLOAT_MAX;
          }

          omega = old_omega;
          step_idx = 0;

          step_idx = LSF_NUMBER_OF_STEPS;
        } else {

          if (step_idx == 0) {
            old_omega = omega;
          }

          step_idx++;
          omega -= steps[step_idx];

          /* Go back one grid step */

          step = steps[step_idx];
        }
      } else {

        /* increment omega until they are of different sign,
           and we know there is at least one root between omega
           and old_omega */
        *old = hlp5;
        omega += step;
      }
    }
  }

  for (i = 0; i < LPC_FILTERORDER; i++) {
    freq[i] = freq[i] * TWO_PI;
  }
}

   /*----------------------------------------------------------------*
    *  conversion from lsf coefficients to lpc coefficients
    *---------------------------------------------------------------*/

void lsf2a(float *a_coef,       /* (o) lpc coefficients */
  float *freq                   /* (i) lsf coefficients */
  )
{
  int i, j;
  float hlp;
  float p[LPC_HALFORDER], q[LPC_HALFORDER];
  float a[LPC_HALFORDER + 1], a1[LPC_HALFORDER], a2[LPC_HALFORDER];
  float b[LPC_HALFORDER + 1], b1[LPC_HALFORDER], b2[LPC_HALFORDER];

  for (i = 0; i < LPC_FILTERORDER; i++) {
    freq[i] = freq[i] * PI2;
  }

  /* Check input for ill-conditioned cases.  This part is not
     found in the TIA standard.  It involves the following 2 IF
     blocks.  If "freq" is judged ill-conditioned, then we first
     modify freq[0] and freq[LPC_HALFORDER-1] (normally
     LPC_HALFORDER = 10 for LPC applications), then we adjust
     the other "freq" values slightly */


  if ((freq[0] <= 0.0) || (freq[LPC_FILTERORDER - 1] >= 0.5)) {


    if (freq[0] <= 0.0) {
      freq[0] = (float) 0.022;
    }


    if (freq[LPC_FILTERORDER - 1] >= 0.5) {
      freq[LPC_FILTERORDER - 1] = (float) 0.499;
    }

    hlp = (freq[LPC_FILTERORDER - 1] - freq[0]) /
      (float) (LPC_FILTERORDER - 1);

    for (i = 1; i < LPC_FILTERORDER; i++) {
      freq[i] = freq[i - 1] + hlp;
    }
  }

  memset(a1, 0, LPC_HALFORDER * sizeof(float));
  memset(a2, 0, LPC_HALFORDER * sizeof(float));
  memset(b1, 0, LPC_HALFORDER * sizeof(float));
  memset(b2, 0, LPC_HALFORDER * sizeof(float));
  memset(a, 0, (LPC_HALFORDER + 1) * sizeof(float));
  memset(b, 0, (LPC_HALFORDER + 1) * sizeof(float));






  /* p[i] and q[i] compute cos(2*pi*omega_{2j}) and
     cos(2*pi*omega_{2j-1} in eqs. 4.2.2.2-1 and 4.2.2.2-2.
     Note that for this code p[i] specifies the coefficients
     used in .Q_A(z) while q[i] specifies the coefficients used
     in .P_A(z) */

  for (i = 0; i < LPC_HALFORDER; i++) {
    p[i] = (float) cos(TWO_PI * freq[2 * i]);
    q[i] = (float) cos(TWO_PI * freq[2 * i + 1]);
  }

  a[0] = 0.25;
  b[0] = 0.25;

  for (i = 0; i < LPC_HALFORDER; i++) {
    a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
    b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
    a2[i] = a1[i];
    a1[i] = a[i];
    b2[i] = b1[i];
    b1[i] = b[i];
  }

  for (j = 0; j < LPC_FILTERORDER; j++) {

    if (j == 0) {
      a[0] = 0.25;
      b[0] = -0.25;
    } else {
      a[0] = b[0] = 0.0;
    }

    for (i = 0; i < LPC_HALFORDER; i++) {
      a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
      b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
      a2[i] = a1[i];
      a1[i] = a[i];
      b2[i] = b1[i];
      b1[i] = b[i];
    }

    a_coef[j + 1] = 2 * (a[LPC_HALFORDER] + b[LPC_HALFORDER]);
  }

  a_coef[0] = 1.0;
}
