ref: 68ee126e7ad40ef2aa9e1039d81608d31211b7f5
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"
#include "define.h"
/* 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, tmp1, tmp2;
silk_float Atmp[ SILK_MAX_ORDER_LPC ];
silk_memcpy( Atmp, A, order * sizeof(silk_float) );
invGain = 1.0;
for( k = order - 1; k > 0; k-- ) {
rc = -Atmp[ k ];
rc_mult1 = 1.0f - rc * rc;
invGain *= rc_mult1;
if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
return 0.0f;
}
rc_mult2 = 1.0f / rc_mult1;
for( n = 0; n < (k + 1) >> 1; n++ ) {
tmp1 = Atmp[ n ];
tmp2 = Atmp[ k - n - 1 ];
Atmp[ n ] = (silk_float)( ( tmp1 - tmp2 * rc ) * rc_mult2 );
Atmp[ k - n - 1 ] = (silk_float)( ( tmp2 - tmp1 * rc ) * rc_mult2 );
}
}
rc = -Atmp[ 0 ];
rc_mult1 = 1.0f - rc * rc;
invGain *= rc_mult1;
if( invGain * MAX_PREDICTION_POWER_GAIN < 1.0f ) {
return 0.0f;
}
return (silk_float)invGain;
}