1/**
2 * LPC utility code
3 * Copyright (c) 2006  Justin Ruggles <justin.ruggles@gmail.com>
4 *
5 * This file is part of Libav.
6 *
7 * Libav 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 * Libav 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 Libav; 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 * LPC analysis type
40 */
41enum FFLPCType {
42    FF_LPC_TYPE_DEFAULT     = -1, ///< use the codec default LPC type
43    FF_LPC_TYPE_NONE        =  0, ///< do not use LPC prediction or use all zero coefficients
44    FF_LPC_TYPE_FIXED       =  1, ///< fixed LPC coefficients
45    FF_LPC_TYPE_LEVINSON    =  2, ///< Levinson-Durbin recursion
46    FF_LPC_TYPE_CHOLESKY    =  3, ///< Cholesky factorization
47    FF_LPC_TYPE_NB              , ///< Not part of ABI
48};
49
50typedef struct LPCContext {
51    int blocksize;
52    int max_order;
53    enum FFLPCType lpc_type;
54    double *windowed_samples;
55
56    /**
57     * Apply a Welch window to an array of input samples.
58     * The output samples have the same scale as the input, but are in double
59     * sample format.
60     * @param data    input samples
61     * @param len     number of input samples
62     * @param w_data  output samples
63     */
64    void (*lpc_apply_welch_window)(const int32_t *data, int len,
65                                   double *w_data);
66    /**
67     * Perform autocorrelation on input samples with delay of 0 to lag.
68     * @param data  input samples.
69     *              constraints: no alignment needed, but must have have at
70     *              least lag*sizeof(double) valid bytes preceding it, and
71     *              size must be at least (len+1)*sizeof(double) if data is
72     *              16-byte aligned or (len+2)*sizeof(double) if data is
73     *              unaligned.
74     * @param len   number of input samples to process
75     * @param lag   maximum delay to calculate
76     * @param autoc output autocorrelation coefficients.
77     *              constraints: array size must be at least lag+1.
78     */
79    void (*lpc_compute_autocorr)(const double *data, int len, int lag,
80                                 double *autoc);
81} LPCContext;
82
83
84/**
85 * Calculate LPC coefficients for multiple orders
86 */
87int ff_lpc_calc_coefs(LPCContext *s,
88                      const int32_t *samples, int blocksize, int min_order,
89                      int max_order, int precision,
90                      int32_t coefs[][MAX_LPC_ORDER], int *shift,
91                      enum FFLPCType lpc_type, int lpc_passes,
92                      int omethod, int max_shift, int zero_shift);
93
94/**
95 * Initialize LPCContext.
96 */
97int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
98                enum FFLPCType lpc_type);
99void ff_lpc_init_x86(LPCContext *s);
100
101/**
102 * Uninitialize LPCContext.
103 */
104void ff_lpc_end(LPCContext *s);
105
106#ifdef LPC_USE_DOUBLE
107#define LPC_TYPE double
108#else
109#define LPC_TYPE float
110#endif
111
112/**
113 * Levinson-Durbin recursion.
114 * Produce LPC coefficients from autocorrelation data.
115 */
116static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
117                                    LPC_TYPE *lpc, int lpc_stride, int fail,
118                                    int normalize)
119{
120    int i, j;
121    LPC_TYPE err;
122    LPC_TYPE *lpc_last = lpc;
123
124    if (normalize)
125        err = *autoc++;
126
127    if (fail && (autoc[max_order - 1] == 0 || err <= 0))
128        return -1;
129
130    for(i=0; i<max_order; i++) {
131        LPC_TYPE r = -autoc[i];
132
133        if (normalize) {
134            for(j=0; j<i; j++)
135                r -= lpc_last[j] * autoc[i-j-1];
136
137            r /= err;
138            err *= 1.0 - (r * r);
139        }
140
141        lpc[i] = r;
142
143        for(j=0; j < (i+1)>>1; j++) {
144            LPC_TYPE f = lpc_last[    j];
145            LPC_TYPE b = lpc_last[i-1-j];
146            lpc[    j] = f + r * b;
147            lpc[i-1-j] = b + r * f;
148        }
149
150        if (fail && err < 0)
151            return -1;
152
153        lpc_last = lpc;
154        lpc += lpc_stride;
155    }
156
157    return 0;
158}
159
160#endif /* AVCODEC_LPC_H */
161