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26***********************************************************************/
27
28#ifdef HAVE_CONFIG_H
29#include "config.h"
30#endif
31
32#include "SigProc_FLP.h"
33#include "tuning_parameters.h"
34#include "define.h"
35
36#define MAX_FRAME_SIZE              384 /* subfr_length * nb_subfr = ( 0.005 * 16000 + 16 ) * 4 = 384*/
37
38/* Compute reflection coefficients from input signal */
39silk_float silk_burg_modified_FLP(          /* O    returns residual energy                                     */
40    silk_float          A[],                /* O    prediction coefficients (length order)                      */
41    const silk_float    x[],                /* I    input signal, length: nb_subfr*(D+L_sub)                    */
42    const silk_float    minInvGain,         /* I    minimum inverse prediction gain                             */
43    const opus_int      subfr_length,       /* I    input signal subframe length (incl. D preceding samples)    */
44    const opus_int      nb_subfr,           /* I    number of subframes stacked in x                            */
45    const opus_int      D                   /* I    order                                                       */
46)
47{
48    opus_int         k, n, s, reached_max_gain;
49    double           C0, invGain, num, nrg_f, nrg_b, rc, Atmp, tmp1, tmp2;
50    const silk_float *x_ptr;
51    double           C_first_row[ SILK_MAX_ORDER_LPC ], C_last_row[ SILK_MAX_ORDER_LPC ];
52    double           CAf[ SILK_MAX_ORDER_LPC + 1 ], CAb[ SILK_MAX_ORDER_LPC + 1 ];
53    double           Af[ SILK_MAX_ORDER_LPC ];
54
55    silk_assert( subfr_length * nb_subfr <= MAX_FRAME_SIZE );
56
57    /* Compute autocorrelations, added over subframes */
58    C0 = silk_energy_FLP( x, nb_subfr * subfr_length );
59    silk_memset( C_first_row, 0, SILK_MAX_ORDER_LPC * sizeof( double ) );
60    for( s = 0; s < nb_subfr; s++ ) {
61        x_ptr = x + s * subfr_length;
62        for( n = 1; n < D + 1; n++ ) {
63            C_first_row[ n - 1 ] += silk_inner_product_FLP( x_ptr, x_ptr + n, subfr_length - n );
64        }
65    }
66    silk_memcpy( C_last_row, C_first_row, SILK_MAX_ORDER_LPC * sizeof( double ) );
67
68    /* Initialize */
69    CAb[ 0 ] = CAf[ 0 ] = C0 + FIND_LPC_COND_FAC * C0 + 1e-9f;
70    invGain = 1.0f;
71    reached_max_gain = 0;
72    for( n = 0; n < D; n++ ) {
73        /* Update first row of correlation matrix (without first element) */
74        /* Update last row of correlation matrix (without last element, stored in reversed order) */
75        /* Update C * Af */
76        /* Update C * flipud(Af) (stored in reversed order) */
77        for( s = 0; s < nb_subfr; s++ ) {
78            x_ptr = x + s * subfr_length;
79            tmp1 = x_ptr[ n ];
80            tmp2 = x_ptr[ subfr_length - n - 1 ];
81            for( k = 0; k < n; k++ ) {
82                C_first_row[ k ] -= x_ptr[ n ] * x_ptr[ n - k - 1 ];
83                C_last_row[ k ]  -= x_ptr[ subfr_length - n - 1 ] * x_ptr[ subfr_length - n + k ];
84                Atmp = Af[ k ];
85                tmp1 += x_ptr[ n - k - 1 ] * Atmp;
86                tmp2 += x_ptr[ subfr_length - n + k ] * Atmp;
87            }
88            for( k = 0; k <= n; k++ ) {
89                CAf[ k ] -= tmp1 * x_ptr[ n - k ];
90                CAb[ k ] -= tmp2 * x_ptr[ subfr_length - n + k - 1 ];
91            }
92        }
93        tmp1 = C_first_row[ n ];
94        tmp2 = C_last_row[ n ];
95        for( k = 0; k < n; k++ ) {
96            Atmp = Af[ k ];
97            tmp1 += C_last_row[  n - k - 1 ] * Atmp;
98            tmp2 += C_first_row[ n - k - 1 ] * Atmp;
99        }
100        CAf[ n + 1 ] = tmp1;
101        CAb[ n + 1 ] = tmp2;
102
103        /* Calculate nominator and denominator for the next order reflection (parcor) coefficient */
104        num = CAb[ n + 1 ];
105        nrg_b = CAb[ 0 ];
106        nrg_f = CAf[ 0 ];
107        for( k = 0; k < n; k++ ) {
108            Atmp = Af[ k ];
109            num   += CAb[ n - k ] * Atmp;
110            nrg_b += CAb[ k + 1 ] * Atmp;
111            nrg_f += CAf[ k + 1 ] * Atmp;
112        }
113        silk_assert( nrg_f > 0.0 );
114        silk_assert( nrg_b > 0.0 );
115
116        /* Calculate the next order reflection (parcor) coefficient */
117        rc = -2.0 * num / ( nrg_f + nrg_b );
118        silk_assert( rc > -1.0 && rc < 1.0 );
119
120        /* Update inverse prediction gain */
121        tmp1 = invGain * ( 1.0 - rc * rc );
122        if( tmp1 <= minInvGain ) {
123            /* Max prediction gain exceeded; set reflection coefficient such that max prediction gain is exactly hit */
124            rc = sqrt( 1.0 - minInvGain / invGain );
125            if( num > 0 ) {
126                /* Ensure adjusted reflection coefficients has the original sign */
127                rc = -rc;
128            }
129            invGain = minInvGain;
130            reached_max_gain = 1;
131        } else {
132            invGain = tmp1;
133        }
134
135        /* Update the AR coefficients */
136        for( k = 0; k < (n + 1) >> 1; k++ ) {
137            tmp1 = Af[ k ];
138            tmp2 = Af[ n - k - 1 ];
139            Af[ k ]         = tmp1 + rc * tmp2;
140            Af[ n - k - 1 ] = tmp2 + rc * tmp1;
141        }
142        Af[ n ] = rc;
143
144        if( reached_max_gain ) {
145            /* Reached max prediction gain; set remaining coefficients to zero and exit loop */
146            for( k = n + 1; k < D; k++ ) {
147                Af[ k ] = 0.0;
148            }
149            break;
150        }
151
152        /* Update C * Af and C * Ab */
153        for( k = 0; k <= n + 1; k++ ) {
154            tmp1 = CAf[ k ];
155            CAf[ k ]          += rc * CAb[ n - k + 1 ];
156            CAb[ n - k + 1  ] += rc * tmp1;
157        }
158    }
159
160    if( reached_max_gain ) {
161        /* Convert to silk_float */
162        for( k = 0; k < D; k++ ) {
163            A[ k ] = (silk_float)( -Af[ k ] );
164        }
165        /* Subtract energy of preceding samples from C0 */
166        for( s = 0; s < nb_subfr; s++ ) {
167            C0 -= silk_energy_FLP( x + s * subfr_length, D );
168        }
169        /* Approximate residual energy */
170        nrg_f = C0 * invGain;
171    } else {
172        /* Compute residual energy and store coefficients as silk_float */
173        nrg_f = CAf[ 0 ];
174        tmp1 = 1.0;
175        for( k = 0; k < D; k++ ) {
176            Atmp = Af[ k ];
177            nrg_f += CAf[ k + 1 ] * Atmp;
178            tmp1  += Atmp * Atmp;
179            A[ k ] = (silk_float)(-Atmp);
180        }
181        nrg_f -= FIND_LPC_COND_FAC * C0 * tmp1;
182    }
183
184    /* Return residual energy */
185    return (silk_float)nrg_f;
186}
187