1/**
2 * LPC utility code
3 * Copyright (c) 2006  Justin Ruggles <justin.ruggles@gmail.com>
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#ifndef AVCODEC_LPC_H
23#define AVCODEC_LPC_H
24
25#include <stdint.h>
26#include "dsputil.h"
27
28#define ORDER_METHOD_EST     0
29#define ORDER_METHOD_2LEVEL  1
30#define ORDER_METHOD_4LEVEL  2
31#define ORDER_METHOD_8LEVEL  3
32#define ORDER_METHOD_SEARCH  4
33#define ORDER_METHOD_LOG     5
34
35#define MIN_LPC_ORDER        1
36#define MAX_LPC_ORDER       32
37
38
39/**
40 * Calculate LPC coefficients for multiple orders
41 */
42int ff_lpc_calc_coefs(DSPContext *s,
43                      const int32_t *samples, int blocksize, int min_order,
44                      int max_order, int precision,
45                      int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
46                      int omethod, int max_shift, int zero_shift);
47
48void ff_lpc_compute_autocorr(const int32_t *data, int len, int lag,
49                             double *autoc);
50
51#ifdef LPC_USE_DOUBLE
52#define LPC_TYPE double
53#else
54#define LPC_TYPE float
55#endif
56
57/**
58 * Levinson-Durbin recursion.
59 * Produces LPC coefficients from autocorrelation data.
60 */
61static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
62                                    LPC_TYPE *lpc, int lpc_stride, int fail,
63                                    int normalize)
64{
65    int i, j;
66    LPC_TYPE err;
67    LPC_TYPE *lpc_last = lpc;
68
69    if (normalize)
70        err = *autoc++;
71
72    if (fail && (autoc[max_order - 1] == 0 || err <= 0))
73        return -1;
74
75    for(i=0; i<max_order; i++) {
76        LPC_TYPE r = -autoc[i];
77
78        if (normalize) {
79            for(j=0; j<i; j++)
80                r -= lpc_last[j] * autoc[i-j-1];
81
82            r /= err;
83            err *= 1.0 - (r * r);
84        }
85
86        lpc[i] = r;
87
88        for(j=0; j < (i+1)>>1; j++) {
89            LPC_TYPE f = lpc_last[    j];
90            LPC_TYPE b = lpc_last[i-1-j];
91            lpc[    j] = f + r * b;
92            lpc[i-1-j] = b + r * f;
93        }
94
95        if (fail && err < 0)
96            return -1;
97
98        lpc_last = lpc;
99        lpc += lpc_stride;
100    }
101
102    return 0;
103}
104
105#endif /* AVCODEC_LPC_H */
106