ref: 8a8b76efeeccaccf402b0b2b4e469980d0a48311
dir: /src_SigProc_FIX/SKP_Silk_biquad_alt.c/
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/* *
* SKP_Silk_biquad_alt.c *
* *
* Second order ARMA filter *
* Can handle slowly varying filter coefficients *
* */
#include "SKP_Silk_SigProc_FIX.h"
/* Second order ARMA filter, alternative implementation */
void SKP_Silk_biquad_alt(
const SKP_int16 *in, /* I: Input signal */
const SKP_int32 *B_Q28, /* I: MA coefficients [3] */
const SKP_int32 *A_Q28, /* I: AR coefficients [2] */
SKP_int32 *S, /* I/O: State vector [2] */
SKP_int16 *out, /* O: Output signal */
const SKP_int32 len /* I: Signal length (must be even) */
)
{
/* DIRECT FORM II TRANSPOSED (uses 2 element state vector) */
SKP_int k;
SKP_int32 inval, A0_U_Q28, A0_L_Q28, A1_U_Q28, A1_L_Q28, out32_Q14;
/* Negate A_Q28 values and split in two parts */
A0_L_Q28 = ( -A_Q28[ 0 ] ) & 0x00003FFF; /* lower part */
A0_U_Q28 = SKP_RSHIFT( -A_Q28[ 0 ], 14 ); /* upper part */
A1_L_Q28 = ( -A_Q28[ 1 ] ) & 0x00003FFF; /* lower part */
A1_U_Q28 = SKP_RSHIFT( -A_Q28[ 1 ], 14 ); /* upper part */
for( k = 0; k < len; k++ ) {
/* S[ 0 ], S[ 1 ]: Q12 */
inval = in[ k ];
out32_Q14 = SKP_LSHIFT( SKP_SMLAWB( S[ 0 ], B_Q28[ 0 ], inval ), 2 );
S[ 0 ] = S[1] + SKP_RSHIFT_ROUND( SKP_SMULWB( out32_Q14, A0_L_Q28 ), 14 );
S[ 0 ] = SKP_SMLAWB( S[ 0 ], out32_Q14, A0_U_Q28 );
S[ 0 ] = SKP_SMLAWB( S[ 0 ], B_Q28[ 1 ], inval);
S[ 1 ] = SKP_RSHIFT_ROUND( SKP_SMULWB( out32_Q14, A1_L_Q28 ), 14 );
S[ 1 ] = SKP_SMLAWB( S[ 1 ], out32_Q14, A1_U_Q28 );
S[ 1 ] = SKP_SMLAWB( S[ 1 ], B_Q28[ 2 ], inval );
/* Scale back to Q0 and saturate */
out[ k ] = (SKP_int16)SKP_SAT16( SKP_RSHIFT( out32_Q14 + (1<<14) - 1, 14 ) );
}
}