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 */
41 struct 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 */
53 struct 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 */
64 struct fir_float_state_t {
65 int taps;
66 int curr_pos;
67 const float *coeffs;
68 float *history;
69 };
70
fir16_create(struct fir16_state_t * fir,const int16_t * coeffs,int taps)71 static 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
fir16_flush(struct fir16_state_t * fir)81 static inline void fir16_flush(struct fir16_state_t *fir)
82 {
83 memset(fir->history, 0, fir->taps * sizeof(int16_t));
84 }
85
fir16_free(struct fir16_state_t * fir)86 static inline void fir16_free(struct fir16_state_t *fir)
87 {
88 kfree(fir->history);
89 }
90
fir16(struct fir16_state_t * fir,int16_t sample)91 static 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
fir32_create(struct fir32_state_t * fir,const int32_t * coeffs,int taps)113 static 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
fir32_flush(struct fir32_state_t * fir)123 static inline void fir32_flush(struct fir32_state_t *fir)
124 {
125 memset(fir->history, 0, fir->taps * sizeof(int16_t));
126 }
127
fir32_free(struct fir32_state_t * fir)128 static inline void fir32_free(struct fir32_state_t *fir)
129 {
130 kfree(fir->history);
131 }
132
fir32(struct fir32_state_t * fir,int16_t sample)133 static 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