ref: 105d751c940c3c6741b5796ba440400b85525b81
dir: /silk/SKP_Silk_LPC_stabilize.c/
/***********************************************************************
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***********************************************************************/
#include "SKP_Silk_typedef.h"
#include "SKP_Silk_SigProc_FIX.h"
#define LPC_STABILIZE_LPC_MAX_ABS_VALUE_Q16 ( ( (SKP_int32)SKP_int16_MAX ) << 4 )
/* LPC stabilizer, for a single input data vector */
void SKP_Silk_LPC_stabilize(
SKP_int16 *a_Q12, /* O stabilized LPC vector [L] */
SKP_int32 *a_Q16, /* I LPC vector [L] */
const SKP_int32 bwe_Q16, /* I Bandwidth expansion factor */
const SKP_int L /* I Number of LPC parameters in the input vector */
)
{
SKP_int32 maxabs, absval, sc_Q16;
SKP_int i, idx = 0;
SKP_int32 invGain_Q30;
SKP_Silk_bwexpander_32( a_Q16, L, bwe_Q16 );
/***************************/
/* Limit range of the LPCs */
/***************************/
/* Limit the maximum absolute value of the prediction coefficients */
while( SKP_TRUE ) {
/* Find maximum absolute value and its index */
maxabs = SKP_int32_MIN;
for( i = 0; i < L; i++ ) {
absval = SKP_abs( a_Q16[ i ] );
if( absval > maxabs ) {
maxabs = absval;
idx = i;
}
}
if( maxabs >= LPC_STABILIZE_LPC_MAX_ABS_VALUE_Q16 ) {
/* Reduce magnitude of prediction coefficients */
sc_Q16 = SKP_DIV32( SKP_int32_MAX, SKP_RSHIFT( maxabs, 4 ) );
sc_Q16 = 65536 - sc_Q16;
sc_Q16 = SKP_DIV32( sc_Q16, idx + 1 );
sc_Q16 = 65536 - sc_Q16;
sc_Q16 = SKP_LSHIFT( SKP_SMULWB( sc_Q16, 32604 ), 1 ); // 0.995 in Q16
SKP_Silk_bwexpander_32( a_Q16, L, sc_Q16 );
} else {
break;
}
}
/* Convert to 16 bit Q12 */
for( i = 0; i < L; i++ ) {
a_Q12[ i ] = (SKP_int16)SKP_RSHIFT_ROUND( a_Q16[ i ], 4 );
}
/**********************/
/* Ensure stable LPCs */
/**********************/
while( SKP_Silk_LPC_inverse_pred_gain( &invGain_Q30, a_Q12, L ) == 1 ) {
SKP_Silk_bwexpander( a_Q12, L, 65339 ); // 0.997 in Q16
}
}
void SKP_Silk_LPC_fit(
SKP_int16 *a_QQ, /* O Stabilized LPC vector, Q(24-rshift) [L] */
SKP_int32 *a_Q24, /* I LPC vector [L] */
const SKP_int QQ, /* I Q domain of output LPC vector */
const SKP_int L /* I Number of LPC parameters in the input vector */
)
{
SKP_int i, rshift, idx = 0;
SKP_int32 maxabs, absval, sc_Q16;
rshift = 24 - QQ;
/***************************/
/* Limit range of the LPCs */
/***************************/
/* Limit the maximum absolute value of the prediction coefficients */
while( SKP_TRUE ) {
/* Find maximum absolute value and its index; assumes stable coefficients */
/* so that only the first half need to be tested */
maxabs = SKP_int32_MIN;
for( i = 1; i < L / 2; i++ ) {
absval = SKP_abs( a_Q24[ i ] );
if( absval > maxabs ) {
maxabs = absval;
idx = i;
}
}
maxabs = SKP_RSHIFT( maxabs, rshift );
if( maxabs >= SKP_int16_MAX ) {
/* Reduce magnitude of prediction coefficients */
maxabs = SKP_min( maxabs, 98369 ); // ( SKP_int32_MAX / ( 65470 >> 2 ) ) + SKP_int16_MAX = 98369
sc_Q16 = 65470 - SKP_DIV32( SKP_MUL( 65470 >> 2, maxabs - SKP_int16_MAX ),
SKP_RSHIFT32( SKP_MUL( maxabs, idx + 1), 2 ) );
SKP_Silk_bwexpander_32( a_Q24, L, sc_Q16 );
} else {
break;
}
}
/* Convert to 16 bit Q(24-rshift) */
SKP_assert( rshift > 0 );
SKP_assert( rshift < 31 );
for( i = 0; i < L; i++ ) {
a_QQ[ i ] = (SKP_int16)SKP_RSHIFT_ROUND( a_Q24[ i ], rshift );
}
}