asterisk/codecs/ilbc/lsf.c

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

    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"
#include "lsf.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;


}