ref: c77b96333b471c7b8a89852ee941e6a8987751b4
dir: /silk/SKP_Silk_resampler_private_ARMA4.c/
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/* *
* SKP_Silk_resampler_private_ARMA4.c *
* *
* Fourth order ARMA filter, applies 64x gain *
* *
* Copyright 2010 (c), Skype Limited *
* */
#include "SKP_Silk_SigProc_FIX.h"
#include "SKP_Silk_resampler_private.h"
/* Fourth order ARMA filter */
/* Internally operates as two biquad filters in sequence. */
/* Coeffients are stored in a packed format: */
/* { B1_Q14[1], B2_Q14[1], -A1_Q14[1], -A1_Q14[2], -A2_Q14[1], -A2_Q14[2], gain_Q16 } */
/* where it is assumed that B*_Q14[0], B*_Q14[2], A*_Q14[0] are all 16384 */
void SKP_Silk_resampler_private_ARMA4(
SKP_int32 S[], /* I/O: State vector [ 4 ] */
SKP_int16 out[], /* O: Output signal */
const SKP_int16 in[], /* I: Input signal */
const SKP_int16 Coef[], /* I: ARMA coefficients [ 7 ] */
SKP_int32 len /* I: Signal length */
)
{
SKP_int32 k;
SKP_int32 in_Q8, out1_Q8, out2_Q8, X;
for( k = 0; k < len; k++ ) {
in_Q8 = SKP_LSHIFT32( (SKP_int32)in[ k ], 8 );
/* Outputs of first and second biquad */
out1_Q8 = SKP_ADD_LSHIFT32( in_Q8, S[ 0 ], 2 );
out2_Q8 = SKP_ADD_LSHIFT32( out1_Q8, S[ 2 ], 2 );
/* Update states, which are stored in Q6. Coefficients are in Q14 here */
X = SKP_SMLAWB( S[ 1 ], in_Q8, Coef[ 0 ] );
S[ 0 ] = SKP_SMLAWB( X, out1_Q8, Coef[ 2 ] );
X = SKP_SMLAWB( S[ 3 ], out1_Q8, Coef[ 1 ] );
S[ 2 ] = SKP_SMLAWB( X, out2_Q8, Coef[ 4 ] );
S[ 1 ] = SKP_SMLAWB( SKP_RSHIFT32( in_Q8, 2 ), out1_Q8, Coef[ 3 ] );
S[ 3 ] = SKP_SMLAWB( SKP_RSHIFT32( out1_Q8, 2 ), out2_Q8, Coef[ 5 ] );
/* Apply gain and store to output. The coefficient is in Q16 */
out[ k ] = (SKP_int16)SKP_SAT16( SKP_RSHIFT32( SKP_SMLAWB( 128, out2_Q8, Coef[ 6 ] ), 8 ) );
}
}