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| |
| /* * |
| * silk_biquad_alt.c * |
| * * |
| * Second order ARMA filter * |
| * Can handle slowly varying filter coefficients * |
| * */ |
| |
| #ifdef HAVE_CONFIG_H |
| #include "config.h" |
| #endif |
| |
| #include "SigProc_FIX.h" |
| |
| /* Second order ARMA filter, alternative implementation */ |
| void silk_biquad_alt( |
| const opus_int16 *in, /* I input signal */ |
| const opus_int32 *B_Q28, /* I MA coefficients [3] */ |
| const opus_int32 *A_Q28, /* I AR coefficients [2] */ |
| opus_int32 *S, /* I/O State vector [2] */ |
| opus_int16 *out, /* O output signal */ |
| const opus_int32 len, /* I signal length (must be even) */ |
| opus_int stride /* I Operate on interleaved signal if > 1 */ |
| ) |
| { |
| /* DIRECT FORM II TRANSPOSED (uses 2 element state vector) */ |
| opus_int k; |
| opus_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 = silk_RSHIFT( -A_Q28[ 0 ], 14 ); /* upper part */ |
| A1_L_Q28 = ( -A_Q28[ 1 ] ) & 0x00003FFF; /* lower part */ |
| A1_U_Q28 = silk_RSHIFT( -A_Q28[ 1 ], 14 ); /* upper part */ |
| |
| for( k = 0; k < len; k++ ) { |
| /* S[ 0 ], S[ 1 ]: Q12 */ |
| inval = in[ k * stride ]; |
| out32_Q14 = silk_LSHIFT( silk_SMLAWB( S[ 0 ], B_Q28[ 0 ], inval ), 2 ); |
| |
| S[ 0 ] = S[1] + silk_RSHIFT_ROUND( silk_SMULWB( out32_Q14, A0_L_Q28 ), 14 ); |
| S[ 0 ] = silk_SMLAWB( S[ 0 ], out32_Q14, A0_U_Q28 ); |
| S[ 0 ] = silk_SMLAWB( S[ 0 ], B_Q28[ 1 ], inval); |
| |
| S[ 1 ] = silk_RSHIFT_ROUND( silk_SMULWB( out32_Q14, A1_L_Q28 ), 14 ); |
| S[ 1 ] = silk_SMLAWB( S[ 1 ], out32_Q14, A1_U_Q28 ); |
| S[ 1 ] = silk_SMLAWB( S[ 1 ], B_Q28[ 2 ], inval ); |
| |
| /* Scale back to Q0 and saturate */ |
| out[ k * stride ] = (opus_int16)silk_SAT16( silk_RSHIFT( out32_Q14 + (1<<14) - 1, 14 ) ); |
| } |
| } |