ref: 2852cb1486ca68fe418bdebcda7ecc9581127b4d
dir: /silk/silk_LPC_inv_pred_gain.c/
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#include "silk_SigProc_FIX.h"
#define QA 16
#define A_LIMIT SILK_FIX_CONST( 0.99975, QA )
/* Compute inverse of LPC prediction gain, and */
/* test if LPC coefficients are stable (all poles within unit circle) */
static opus_int LPC_inverse_pred_gain_QA( /* O: Returns 1 if unstable, otherwise 0 */
opus_int32 *invGain_Q30, /* O: Inverse prediction gain, Q30 energy domain */
opus_int32 A_QA[ 2 ][ SILK_MAX_ORDER_LPC ],
/* I: Prediction coefficients */
const opus_int order /* I: Prediction order */
)
{
opus_int k, n, headrm;
opus_int32 rc_Q31, rc_mult1_Q30, rc_mult2_Q16, tmp_QA;
opus_int32 *Aold_QA, *Anew_QA;
Anew_QA = A_QA[ order & 1 ];
*invGain_Q30 = ( 1 << 30 );
for( k = order - 1; k > 0; k-- ) {
/* Check for stability */
if( ( Anew_QA[ k ] > A_LIMIT ) || ( Anew_QA[ k ] < -A_LIMIT ) ) {
return 1;
}
/* Set RC equal to negated AR coef */
rc_Q31 = -SKP_LSHIFT( Anew_QA[ k ], 31 - QA );
/* rc_mult1_Q30 range: [ 1 : 2^30-1 ] */
rc_mult1_Q30 = ( SKP_int32_MAX >> 1 ) - SKP_SMMUL( rc_Q31, rc_Q31 );
SKP_assert( rc_mult1_Q30 > ( 1 << 15 ) ); /* reduce A_LIMIT if fails */
SKP_assert( rc_mult1_Q30 < ( 1 << 30 ) );
/* rc_mult2_Q16 range: [ 2^16 : SKP_int32_MAX ] */
rc_mult2_Q16 = silk_INVERSE32_varQ( rc_mult1_Q30, 46 ); /* 16 = 46 - 30 */
/* Update inverse gain */
/* invGain_Q30 range: [ 0 : 2^30 ] */
*invGain_Q30 = SKP_LSHIFT( SKP_SMMUL( *invGain_Q30, rc_mult1_Q30 ), 2 );
SKP_assert( *invGain_Q30 >= 0 );
SKP_assert( *invGain_Q30 <= ( 1 << 30 ) );
/* Swap pointers */
Aold_QA = Anew_QA;
Anew_QA = A_QA[ k & 1 ];
/* Update AR coefficient */
headrm = silk_CLZ32( rc_mult2_Q16 ) - 1;
rc_mult2_Q16 = SKP_LSHIFT( rc_mult2_Q16, headrm ); /* Q: 16 + headrm */
for( n = 0; n < k; n++ ) {
tmp_QA = Aold_QA[ n ] - SKP_LSHIFT( SKP_SMMUL( Aold_QA[ k - n - 1 ], rc_Q31 ), 1 );
Anew_QA[ n ] = SKP_LSHIFT( SKP_SMMUL( tmp_QA, rc_mult2_Q16 ), 16 - headrm );
}
}
/* Check for stability */
if( ( Anew_QA[ 0 ] > A_LIMIT ) || ( Anew_QA[ 0 ] < -A_LIMIT ) ) {
return 1;
}
/* Set RC equal to negated AR coef */
rc_Q31 = -SKP_LSHIFT( Anew_QA[ 0 ], 31 - QA );
/* Range: [ 1 : 2^30 ] */
rc_mult1_Q30 = ( SKP_int32_MAX >> 1 ) - SKP_SMMUL( rc_Q31, rc_Q31 );
/* Update inverse gain */
/* Range: [ 0 : 2^30 ] */
*invGain_Q30 = SKP_LSHIFT( SKP_SMMUL( *invGain_Q30, rc_mult1_Q30 ), 2 );
SKP_assert( *invGain_Q30 >= 0 );
SKP_assert( *invGain_Q30 <= 1<<30 );
return 0;
}
/* For input in Q12 domain */
opus_int silk_LPC_inverse_pred_gain( /* O: Returns 1 if unstable, otherwise 0 */
opus_int32 *invGain_Q30, /* O: Inverse prediction gain, Q30 energy domain */
const opus_int16 *A_Q12, /* I: Prediction coefficients, Q12 [order] */
const opus_int order /* I: Prediction order */
)
{
opus_int k;
opus_int32 Atmp_QA[ 2 ][ SILK_MAX_ORDER_LPC ];
opus_int32 *Anew_QA;
Anew_QA = Atmp_QA[ order & 1 ];
/* Increase Q domain of the AR coefficients */
for( k = 0; k < order; k++ ) {
Anew_QA[ k ] = SKP_LSHIFT( (opus_int32)A_Q12[ k ], QA - 12 );
}
return LPC_inverse_pred_gain_QA( invGain_Q30, Atmp_QA, order );
}
/* For input in Q24 domain */
opus_int silk_LPC_inverse_pred_gain_Q24( /* O: Returns 1 if unstable, otherwise 0 */
opus_int32 *invGain_Q30, /* O: Inverse prediction gain, Q30 energy domain */
const opus_int32 *A_Q24, /* I: Prediction coefficients, Q24 [order] */
const opus_int order /* I: Prediction order */
)
{
opus_int k;
opus_int32 Atmp_QA[ 2 ][ SILK_MAX_ORDER_LPC ];
opus_int32 *Anew_QA;
Anew_QA = Atmp_QA[ order & 1 ];
/* Increase Q domain of the AR coefficients */
for( k = 0; k < order; k++ ) {
Anew_QA[ k ] = SKP_RSHIFT_ROUND( A_Q24[ k ], 24 - QA );
}
return LPC_inverse_pred_gain_QA( invGain_Q30, Atmp_QA, order );
}