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 */
 53struct 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 */
 65struct 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 */
 76struct fir_float_state_t {
 77	int taps;
 78	int curr_pos;
 79	const float *coeffs;
 80	float *history;
 81};
 82
 83static 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
 93static inline void fir16_flush(struct fir16_state_t *fir)
 94{
 95	memset(fir->history, 0, fir->taps * sizeof(int16_t));
 96}
 97
 98static inline void fir16_free(struct fir16_state_t *fir)
 99{
100	kfree(fir->history);
101}
102
103static 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
125static 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
135static inline void fir32_flush(struct fir32_state_t *fir)
136{
137	memset(fir->history, 0, fir->taps * sizeof(int16_t));
138}
139
140static inline void fir32_free(struct fir32_state_t *fir)
141{
142	kfree(fir->history);
143}
144
145static 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