ref: fe741259c1050baa5c828444dd5a968ed658d1fb
dir: /silk/SKP_Silk_LPC_inv_pred_gain_FLP.c/
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/* *
* SKP_Silk_LPC_inverse_pred_gain.c *
* *
* compute inverse of LPC prediction gain, and *
* test if LPC coefficients are stable (all poles within unit circle) *
* *
* Copyright 2008 (c), Skype Limited *
* */
#include "SKP_Silk_SigProc_FIX.h"
#include "SKP_Silk_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 SKP_Silk_a2k_FLP() */
SKP_int SKP_Silk_LPC_inverse_pred_gain_FLP( /* O: returns 1 if unstable, otherwise 0 */
SKP_float *invGain, /* O: inverse prediction gain, energy domain */
const SKP_float *A, /* I: prediction coefficients [order] */
SKP_int32 order /* I: prediction order */
)
{
SKP_int k, n;
double rc, rc_mult1, rc_mult2;
SKP_float Atmp[ 2 ][ SKP_Silk_MAX_ORDER_LPC ];
SKP_float *Aold, *Anew;
Anew = Atmp[ order & 1 ];
SKP_memcpy( Anew, A, order * sizeof(SKP_float) );
*invGain = 1.0f;
for( k = order - 1; k > 0; k-- ) {
rc = -Anew[ k ];
if (rc > RC_THRESHOLD || rc < -RC_THRESHOLD) {
return 1;
}
rc_mult1 = 1.0f - rc * rc;
rc_mult2 = 1.0f / rc_mult1;
*invGain *= (SKP_float)rc_mult1;
/* swap pointers */
Aold = Anew;
Anew = Atmp[ k & 1 ];
for( n = 0; n < k; n++ ) {
Anew[ n ] = (SKP_float)( ( Aold[ n ] - Aold[ k - n - 1 ] * rc ) * rc_mult2 );
}
}
rc = -Anew[ 0 ];
if ( rc > RC_THRESHOLD || rc < -RC_THRESHOLD ) {
return 1;
}
rc_mult1 = 1.0f - rc * rc;
*invGain *= (SKP_float)rc_mult1;
return 0;
}