drivers/isdn/mISDN/dsp_biquad.h

   1 /*
   2  * SpanDSP - a series of DSP components for telephony
   3  *
   4  * biquad.h - General telephony bi-quad section routines (currently this just
   5  *            handles canonic/type 2 form)
   6  *
   7  * Written by Steve Underwood <steveu@coppice.org>
   8  *
   9  * Copyright (C) 2001 Steve Underwood
  10  *
  11  * All rights reserved.
  12  *
  13  * This program is free software; you can redistribute it and/or modify
  14  * it under the terms of the GNU General Public License as published by
  15  * the Free Software Foundation; either version 2 of the License, or
  16  * (at your option) any later version.
  17  *
  18  * This program is distributed in the hope that it will be useful,
  19  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  20  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21  * GNU General Public License for more details.
  22  *
  23  * You should have received a copy of the GNU General Public License
  24  * along with this program; if not, write to the Free Software
  25  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  26  *
  27  */
  28
  29 struct biquad2_state {
  30         int32_t gain;
  31         int32_t a1;
  32         int32_t a2;
  33         int32_t b1;
  34         int32_t b2;
  35
  36         int32_t z1;
  37         int32_t z2;
  38 };
  39
  40 static inline void biquad2_init(struct biquad2_state *bq,
  41     int32_t gain, int32_t a1, int32_t a2, int32_t b1, int32_t b2)
  42 {
  43         bq->gain = gain;
  44         bq->a1 = a1;
  45         bq->a2 = a2;
  46         bq->b1 = b1;
  47         bq->b2 = b2;
  48
  49         bq->z1 = 0;
  50         bq->z2 = 0;
  51 }
  52
  53 static inline int16_t biquad2(struct biquad2_state *bq, int16_t sample)
  54 {
  55         int32_t y;
  56         int32_t z0;
  57
  58         z0 = sample*bq->gain + bq->z1*bq->a1 + bq->z2*bq->a2;
  59         y = z0 + bq->z1*bq->b1 + bq->z2*bq->b2;
  60
  61         bq->z2 = bq->z1;
  62         bq->z1 = z0 >> 15;
  63         y >>= 15;
  64         return  y;
  65 }