1 /*********************************************************************** 2 Copyright (c) 2006-2011, Skype Limited. All rights reserved. 3 Redistribution and use in source and binary forms, with or without 4 modification, are permitted provided that the following conditions 5 are met: 6 - Redistributions of source code must retain the above copyright notice, 7 this list of conditions and the following disclaimer. 8 - Redistributions in binary form must reproduce the above copyright 9 notice, this list of conditions and the following disclaimer in the 10 documentation and/or other materials provided with the distribution. 11 - Neither the name of Internet Society, IETF or IETF Trust, nor the 12 names of specific contributors, may be used to endorse or promote 13 products derived from this software without specific prior written 14 permission. 15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 16 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 19 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 20 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 21 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 22 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 23 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25 POSSIBILITY OF SUCH DAMAGE. 26 ***********************************************************************/ 27 28 /* * 29 * silk_biquad_alt.c * 30 * * 31 * Second order ARMA filter * 32 * Can handle slowly varying filter coefficients * 33 * */ 34 35 #ifdef HAVE_CONFIG_H 36 #include "config.h" 37 #endif 38 39 #include "SigProc_FIX.h" 40 41 /* Second order ARMA filter, alternative implementation */ 42 void silk_biquad_alt( 43 const opus_int16 *in, /* I input signal */ 44 const opus_int32 *B_Q28, /* I MA coefficients [3] */ 45 const opus_int32 *A_Q28, /* I AR coefficients [2] */ 46 opus_int32 *S, /* I/O State vector [2] */ 47 opus_int16 *out, /* O output signal */ 48 const opus_int32 len, /* I signal length (must be even) */ 49 opus_int stride /* I Operate on interleaved signal if > 1 */ 50 ) 51 { 52 /* DIRECT FORM II TRANSPOSED (uses 2 element state vector) */ 53 opus_int k; 54 opus_int32 inval, A0_U_Q28, A0_L_Q28, A1_U_Q28, A1_L_Q28, out32_Q14; 55 56 /* Negate A_Q28 values and split in two parts */ 57 A0_L_Q28 = ( -A_Q28[ 0 ] ) & 0x00003FFF; /* lower part */ 58 A0_U_Q28 = silk_RSHIFT( -A_Q28[ 0 ], 14 ); /* upper part */ 59 A1_L_Q28 = ( -A_Q28[ 1 ] ) & 0x00003FFF; /* lower part */ 60 A1_U_Q28 = silk_RSHIFT( -A_Q28[ 1 ], 14 ); /* upper part */ 61 62 for( k = 0; k < len; k++ ) { 63 /* S[ 0 ], S[ 1 ]: Q12 */ 64 inval = in[ k * stride ]; 65 out32_Q14 = silk_LSHIFT( silk_SMLAWB( S[ 0 ], B_Q28[ 0 ], inval ), 2 ); 66 67 S[ 0 ] = S[1] + silk_RSHIFT_ROUND( silk_SMULWB( out32_Q14, A0_L_Q28 ), 14 ); 68 S[ 0 ] = silk_SMLAWB( S[ 0 ], out32_Q14, A0_U_Q28 ); 69 S[ 0 ] = silk_SMLAWB( S[ 0 ], B_Q28[ 1 ], inval); 70 71 S[ 1 ] = silk_RSHIFT_ROUND( silk_SMULWB( out32_Q14, A1_L_Q28 ), 14 ); 72 S[ 1 ] = silk_SMLAWB( S[ 1 ], out32_Q14, A1_U_Q28 ); 73 S[ 1 ] = silk_SMLAWB( S[ 1 ], B_Q28[ 2 ], inval ); 74 75 /* Scale back to Q0 and saturate */ 76 out[ k * stride ] = (opus_int16)silk_SAT16( silk_RSHIFT( out32_Q14 + (1<<14) - 1, 14 ) ); 77 } 78 } 79
