ref: ccec752a384cf6ad110ec141f8bb035d14328eee
dir: /silk/float/LPC_inv_pred_gain_FLP.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "SigProc_FIX.h"
#include "SigProc_FLP.h"
#define RC_THRESHOLD 0.9999f
/* compute inverse of LPC prediction gain, and */
/* test if LPC coefficients are stable (all poles within unit circle) */
/* this code is based on silk_a2k_FLP() */
silk_float silk_LPC_inverse_pred_gain_FLP( /* O return inverse prediction gain, energy domain */
const silk_float *A, /* I prediction coefficients [order] */
opus_int32 order /* I prediction order */
)
{
opus_int k, n;
double invGain, rc, rc_mult1, rc_mult2;
silk_float Atmp[ 2 ][ SILK_MAX_ORDER_LPC ];
silk_float *Aold, *Anew;
Anew = Atmp[ order & 1 ];
silk_memcpy( Anew, A, order * sizeof(silk_float) );
invGain = 1.0;
for( k = order - 1; k > 0; k-- ) {
rc = -Anew[ k ];
if( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
return 0.0f;
}
rc_mult1 = 1.0f - rc * rc;
rc_mult2 = 1.0f / rc_mult1;
invGain *= rc_mult1;
/* swap pointers */
Aold = Anew;
Anew = Atmp[ k & 1 ];
for( n = 0; n < k; n++ ) {
Anew[ n ] = (silk_float)( ( Aold[ n ] - Aold[ k - n - 1 ] * rc ) * rc_mult2 );
}
}
rc = -Anew[ 0 ];
if( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
return 0.0f;
}
rc_mult1 = 1.0f - rc * rc;
invGain *= rc_mult1;
return (silk_float)invGain;
}