drivers/misc/echo/fir.h

   1 /*
   2  * SpanDSP - a series of DSP components for telephony
   3  *
   4  * fir.h - General telephony FIR routines
   5  *
   6  * Written by Steve Underwood <steveu@coppice.org>
   7  *
   8  * Copyright (C) 2002 Steve Underwood
   9  *
  10  * All rights reserved.
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License version 2, as
  14  * published by the Free Software Foundation.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  24  */
  25
  26 #if !defined(_FIR_H_)
  27 #define _FIR_H_
  28
  29 /*
  30    Ideas for improvement:
  31
  32    1/ Rewrite filter for dual MAC inner loop.  The issue here is handling
  33    history sample offsets that are 16 bit aligned - the dual MAC needs
  34    32 bit aligmnent.  There are some good examples in libbfdsp.
  35
  36    2/ Use the hardware circular buffer facility tohalve memory usage.
  37
  38    3/ Consider using internal memory.
  39
  40    Using less memory might also improve speed as cache misses will be
  41    reduced. A drop in MIPs and memory approaching 50% should be
  42    possible.
  43
  44    The foreground and background filters currenlty use a total of
  45    about 10 MIPs/ch as measured with speedtest.c on a 256 TAP echo
  46    can.
  47 */
  48
  49 /*
  50  * 16 bit integer FIR descriptor. This defines the working state for a single
  51  * instance of an FIR filter using 16 bit integer coefficients.
  52  */
  53 struct fir16_state_t {
  54         int taps;
  55         int curr_pos;
  56         const int16_t *coeffs;
  57         int16_t *history;
  58 };
  59
  60 /*
  61  * 32 bit integer FIR descriptor. This defines the working state for a single
  62  * instance of an FIR filter using 32 bit integer coefficients, and filtering
  63  * 16 bit integer data.
  64  */
  65 struct fir32_state_t {
  66         int taps;
  67         int curr_pos;
  68         const int32_t *coeffs;
  69         int16_t *history;
  70 };
  71
  72 /*
  73  * Floating point FIR descriptor. This defines the working state for a single
  74  * instance of an FIR filter using floating point coefficients and data.
  75  */
  76 struct fir_float_state_t {
  77         int taps;
  78         int curr_pos;
  79         const float *coeffs;
  80         float *history;
  81 };
  82
  83 static inline const int16_t *fir16_create(struct fir16_state_t *fir,
  84                                               const int16_t *coeffs, int taps)
  85 {
  86         fir->taps = taps;
  87         fir->curr_pos = taps - 1;
  88         fir->coeffs = coeffs;
  89         fir->history = kcalloc(taps, sizeof(int16_t), GFP_KERNEL);
  90         return fir->history;
  91 }
  92
  93 static inline void fir16_flush(struct fir16_state_t *fir)
  94 {
  95         memset(fir->history, 0, fir->taps * sizeof(int16_t));
  96 }
  97
  98 static inline void fir16_free(struct fir16_state_t *fir)
  99 {
 100         kfree(fir->history);
 101 }
 102
 103 static inline int16_t fir16(struct fir16_state_t *fir, int16_t sample)
 104 {
 105         int32_t y;
 106         int i;
 107         int offset1;
 108         int offset2;
 109
 110         fir->history[fir->curr_pos] = sample;
 111
 112         offset2 = fir->curr_pos;
 113         offset1 = fir->taps - offset2;
 114         y = 0;
 115         for (i = fir->taps - 1; i >= offset1; i--)
 116                 y += fir->coeffs[i] * fir->history[i - offset1];
 117         for (; i >= 0; i--)
 118                 y += fir->coeffs[i] * fir->history[i + offset2];
 119         if (fir->curr_pos <= 0)
 120                 fir->curr_pos = fir->taps;
 121         fir->curr_pos--;
 122         return (int16_t) (y >> 15);
 123 }
 124
 125 static inline const int16_t *fir32_create(struct fir32_state_t *fir,
 126                                               const int32_t *coeffs, int taps)
 127 {
 128         fir->taps = taps;
 129         fir->curr_pos = taps - 1;
 130         fir->coeffs = coeffs;
 131         fir->history = kcalloc(taps, sizeof(int16_t), GFP_KERNEL);
 132         return fir->history;
 133 }
 134
 135 static inline void fir32_flush(struct fir32_state_t *fir)
 136 {
 137         memset(fir->history, 0, fir->taps * sizeof(int16_t));
 138 }
 139
 140 static inline void fir32_free(struct fir32_state_t *fir)
 141 {
 142         kfree(fir->history);
 143 }
 144
 145 static inline int16_t fir32(struct fir32_state_t *fir, int16_t sample)
 146 {
 147         int i;
 148         int32_t y;
 149         int offset1;
 150         int offset2;
 151
 152         fir->history[fir->curr_pos] = sample;
 153         offset2 = fir->curr_pos;
 154         offset1 = fir->taps - offset2;
 155         y = 0;
 156         for (i = fir->taps - 1; i >= offset1; i--)
 157                 y += fir->coeffs[i] * fir->history[i - offset1];
 158         for (; i >= 0; i--)
 159                 y += fir->coeffs[i] * fir->history[i + offset2];
 160         if (fir->curr_pos <= 0)
 161                 fir->curr_pos = fir->taps;
 162         fir->curr_pos--;
 163         return (int16_t) (y >> 15);
 164 }
 165
 166 #endif