michael@0: /***********************************************************************
michael@0: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
michael@0: Redistribution and use in source and binary forms, with or without
michael@0: modification, are permitted provided that the following conditions
michael@0: are met:
michael@0: - Redistributions of source code must retain the above copyright notice,
michael@0: this list of conditions and the following disclaimer.
michael@0: - Redistributions in binary form must reproduce the above copyright
michael@0: notice, this list of conditions and the following disclaimer in the
michael@0: documentation and/or other materials provided with the distribution.
michael@0: - Neither the name of Internet Society, IETF or IETF Trust, nor the
michael@0: names of specific contributors, may be used to endorse or promote
michael@0: products derived from this software without specific prior written
michael@0: permission.
michael@0: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
michael@0: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
michael@0: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
michael@0: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
michael@0: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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michael@0: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
michael@0: POSSIBILITY OF SUCH DAMAGE.
michael@0: ***********************************************************************/
michael@0: 
michael@0: /*                                                                      *
michael@0:  * silk_biquad_alt.c                                              *
michael@0:  *                                                                      *
michael@0:  * Second order ARMA filter                                             *
michael@0:  * Can handle slowly varying filter coefficients                        *
michael@0:  *                                                                      */
michael@0: 
michael@0: #ifdef HAVE_CONFIG_H
michael@0: #include "config.h"
michael@0: #endif
michael@0: 
michael@0: #include "SigProc_FIX.h"
michael@0: 
michael@0: /* Second order ARMA filter, alternative implementation */
michael@0: void silk_biquad_alt(
michael@0:     const opus_int16            *in,                /* I     input signal                                               */
michael@0:     const opus_int32            *B_Q28,             /* I     MA coefficients [3]                                        */
michael@0:     const opus_int32            *A_Q28,             /* I     AR coefficients [2]                                        */
michael@0:     opus_int32                  *S,                 /* I/O   State vector [2]                                           */
michael@0:     opus_int16                  *out,               /* O     output signal                                              */
michael@0:     const opus_int32            len,                /* I     signal length (must be even)                               */
michael@0:     opus_int                    stride              /* I     Operate on interleaved signal if > 1                       */
michael@0: )
michael@0: {
michael@0:     /* DIRECT FORM II TRANSPOSED (uses 2 element state vector) */
michael@0:     opus_int   k;
michael@0:     opus_int32 inval, A0_U_Q28, A0_L_Q28, A1_U_Q28, A1_L_Q28, out32_Q14;
michael@0: 
michael@0:     /* Negate A_Q28 values and split in two parts */
michael@0:     A0_L_Q28 = ( -A_Q28[ 0 ] ) & 0x00003FFF;        /* lower part */
michael@0:     A0_U_Q28 = silk_RSHIFT( -A_Q28[ 0 ], 14 );      /* upper part */
michael@0:     A1_L_Q28 = ( -A_Q28[ 1 ] ) & 0x00003FFF;        /* lower part */
michael@0:     A1_U_Q28 = silk_RSHIFT( -A_Q28[ 1 ], 14 );      /* upper part */
michael@0: 
michael@0:     for( k = 0; k < len; k++ ) {
michael@0:         /* S[ 0 ], S[ 1 ]: Q12 */
michael@0:         inval = in[ k * stride ];
michael@0:         out32_Q14 = silk_LSHIFT( silk_SMLAWB( S[ 0 ], B_Q28[ 0 ], inval ), 2 );
michael@0: 
michael@0:         S[ 0 ] = S[1] + silk_RSHIFT_ROUND( silk_SMULWB( out32_Q14, A0_L_Q28 ), 14 );
michael@0:         S[ 0 ] = silk_SMLAWB( S[ 0 ], out32_Q14, A0_U_Q28 );
michael@0:         S[ 0 ] = silk_SMLAWB( S[ 0 ], B_Q28[ 1 ], inval);
michael@0: 
michael@0:         S[ 1 ] = silk_RSHIFT_ROUND( silk_SMULWB( out32_Q14, A1_L_Q28 ), 14 );
michael@0:         S[ 1 ] = silk_SMLAWB( S[ 1 ], out32_Q14, A1_U_Q28 );
michael@0:         S[ 1 ] = silk_SMLAWB( S[ 1 ], B_Q28[ 2 ], inval );
michael@0: 
michael@0:         /* Scale back to Q0 and saturate */
michael@0:         out[ k * stride ] = (opus_int16)silk_SAT16( silk_RSHIFT( out32_Q14 + (1<<14) - 1, 14 ) );
michael@0:     }
michael@0: }