lsf.c

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

 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;
 }