drivers/isdn/mISDN/dsp_biquad.h

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /*
   3  * SpanDSP - a series of DSP components for telephony
   4  *
   5  * biquad.h - General telephony bi-quad section routines (currently this just
   6  *            handles canonic/type 2 form)
   7  *
   8  * Written by Steve Underwood <steveu@coppice.org>
   9  *
  10  * Copyright (C) 2001 Steve Underwood
  11  *
  12  * All rights reserved.
  13  */
  14
  15 struct biquad2_state {
  16         int32_t gain;
  17         int32_t a1;
  18         int32_t a2;
  19         int32_t b1;
  20         int32_t b2;
  21
  22         int32_t z1;
  23         int32_t z2;
  24 };
  25
  26 static inline void biquad2_init(struct biquad2_state *bq,
  27                                 int32_t gain, int32_t a1, int32_t a2, int32_t b1, int32_t b2)
  28 {
  29         bq->gain = gain;
  30         bq->a1 = a1;
  31         bq->a2 = a2;
  32         bq->b1 = b1;
  33         bq->b2 = b2;
  34
  35         bq->z1 = 0;
  36         bq->z2 = 0;
  37 }
  38
  39 static inline int16_t biquad2(struct biquad2_state *bq, int16_t sample)
  40 {
  41         int32_t y;
  42         int32_t z0;
  43
  44         z0 = sample * bq->gain + bq->z1 * bq->a1 + bq->z2 * bq->a2;
  45         y = z0 + bq->z1 * bq->b1 + bq->z2 * bq->b2;
  46
  47         bq->z2 = bq->z1;
  48         bq->z1 = z0 >> 15;
  49         y >>= 15;
  50         return  y;
  51 }