1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * SpanDSP - a series of DSP components for telephony
4 *
5 * fir.h - General telephony FIR routines
6 *
7 * Written by Steve Underwood <steveu@coppice.org>
8 *
9 * Copyright (C) 2002 Steve Underwood
10 *
11 * All rights reserved.
12 */
13
14#if !defined(_FIR_H_)
15#define _FIR_H_
16
17/*
18   Ideas for improvement:
19
20   1/ Rewrite filter for dual MAC inner loop.  The issue here is handling
21   history sample offsets that are 16 bit aligned - the dual MAC needs
22   32 bit aligmnent.  There are some good examples in libbfdsp.
23
24   2/ Use the hardware circular buffer facility tohalve memory usage.
25
26   3/ Consider using internal memory.
27
28   Using less memory might also improve speed as cache misses will be
29   reduced. A drop in MIPs and memory approaching 50% should be
30   possible.
31
32   The foreground and background filters currenlty use a total of
33   about 10 MIPs/ch as measured with speedtest.c on a 256 TAP echo
34   can.
35*/
36
37/*
38 * 16 bit integer FIR descriptor. This defines the working state for a single
39 * instance of an FIR filter using 16 bit integer coefficients.
40 */
41struct fir16_state_t {
42	int taps;
43	int curr_pos;
44	const int16_t *coeffs;
45	int16_t *history;
46};
47
48/*
49 * 32 bit integer FIR descriptor. This defines the working state for a single
50 * instance of an FIR filter using 32 bit integer coefficients, and filtering
51 * 16 bit integer data.
52 */
53struct fir32_state_t {
54	int taps;
55	int curr_pos;
56	const int32_t *coeffs;
57	int16_t *history;
58};
59
60/*
61 * Floating point FIR descriptor. This defines the working state for a single
62 * instance of an FIR filter using floating point coefficients and data.
63 */
64struct fir_float_state_t {
65	int taps;
66	int curr_pos;
67	const float *coeffs;
68	float *history;
69};
70
71static inline const int16_t *fir16_create(struct fir16_state_t *fir,
72					      const int16_t *coeffs, int taps)
73{
74	fir->taps = taps;
75	fir->curr_pos = taps - 1;
76	fir->coeffs = coeffs;
77	fir->history = kcalloc(taps, sizeof(int16_t), GFP_KERNEL);
78	return fir->history;
79}
80
81static inline void fir16_flush(struct fir16_state_t *fir)
82{
83	memset(fir->history, 0, fir->taps * sizeof(int16_t));
84}
85
86static inline void fir16_free(struct fir16_state_t *fir)
87{
88	kfree(fir->history);
89}
90
91static inline int16_t fir16(struct fir16_state_t *fir, int16_t sample)
92{
93	int32_t y;
94	int i;
95	int offset1;
96	int offset2;
97
98	fir->history[fir->curr_pos] = sample;
99
100	offset2 = fir->curr_pos;
101	offset1 = fir->taps - offset2;
102	y = 0;
103	for (i = fir->taps - 1; i >= offset1; i--)
104		y += fir->coeffs[i] * fir->history[i - offset1];
105	for (; i >= 0; i--)
106		y += fir->coeffs[i] * fir->history[i + offset2];
107	if (fir->curr_pos <= 0)
108		fir->curr_pos = fir->taps;
109	fir->curr_pos--;
110	return (int16_t) (y >> 15);
111}
112
113static inline const int16_t *fir32_create(struct fir32_state_t *fir,
114					      const int32_t *coeffs, int taps)
115{
116	fir->taps = taps;
117	fir->curr_pos = taps - 1;
118	fir->coeffs = coeffs;
119	fir->history = kcalloc(taps, sizeof(int16_t), GFP_KERNEL);
120	return fir->history;
121}
122
123static inline void fir32_flush(struct fir32_state_t *fir)
124{
125	memset(fir->history, 0, fir->taps * sizeof(int16_t));
126}
127
128static inline void fir32_free(struct fir32_state_t *fir)
129{
130	kfree(fir->history);
131}
132
133static inline int16_t fir32(struct fir32_state_t *fir, int16_t sample)
134{
135	int i;
136	int32_t y;
137	int offset1;
138	int offset2;
139
140	fir->history[fir->curr_pos] = sample;
141	offset2 = fir->curr_pos;
142	offset1 = fir->taps - offset2;
143	y = 0;
144	for (i = fir->taps - 1; i >= offset1; i--)
145		y += fir->coeffs[i] * fir->history[i - offset1];
146	for (; i >= 0; i--)
147		y += fir->coeffs[i] * fir->history[i + offset2];
148	if (fir->curr_pos <= 0)
149		fir->curr_pos = fir->taps;
150	fir->curr_pos--;
151	return (int16_t) (y >> 15);
152}
153
154#endif
155