asterisk/codecs/ilbc/lsf.c

 
/****************************************************************** 
 
    iLBC Speech Coder ANSI-C Source Code 
 
    lsf.c  
 
    Copyright (c) 2001, 
    Global IP Sound AB. 
    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; 
}