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 "libavutil/avassert.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_buffer;
55    double *windowed_samples;
56
57    /**
58     * Apply a Welch window to an array of input samples.
59     * The output samples have the same scale as the input, but are in double
60     * sample format.
61     * @param data    input samples
62     * @param len     number of input samples
63     * @param w_data  output samples
64     */
65    void (*lpc_apply_welch_window)(const int32_t *data, int len,
66                                   double *w_data);
67    /**
68     * Perform autocorrelation on input samples with delay of 0 to lag.
69     * @param data  input samples.
70     *              constraints: no alignment needed, but must have at
71     *              least lag*sizeof(double) valid bytes preceding it, and
72     *              size must be at least (len+1)*sizeof(double) if data is
73     *              16-byte aligned or (len+2)*sizeof(double) if data is
74     *              unaligned.
75     * @param len   number of input samples to process
76     * @param lag   maximum delay to calculate
77     * @param autoc output autocorrelation coefficients.
78     *              constraints: array size must be at least lag+1.
79     */
80    void (*lpc_compute_autocorr)(const double *data, int len, int lag,
81                                 double *autoc);
82} LPCContext;
83
84
85/**
86 * Calculate LPC coefficients for multiple orders
87 */
88int ff_lpc_calc_coefs(LPCContext *s,
89                      const int32_t *samples, int blocksize, int min_order,
90                      int max_order, int precision,
91                      int32_t coefs[][MAX_LPC_ORDER], int *shift,
92                      enum FFLPCType lpc_type, int lpc_passes,
93                      int omethod, int max_shift, int zero_shift);
94
95int ff_lpc_calc_ref_coefs(LPCContext *s,
96                          const int32_t *samples, int order, double *ref);
97
98/**
99 * Initialize LPCContext.
100 */
101int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
102                enum FFLPCType lpc_type);
103void ff_lpc_init_x86(LPCContext *s);
104
105/**
106 * Uninitialize LPCContext.
107 */
108void ff_lpc_end(LPCContext *s);
109
110#ifdef LPC_USE_DOUBLE
111#define LPC_TYPE double
112#else
113#define LPC_TYPE float
114#endif
115
116/**
117 * Schur recursion.
118 * Produces reflection coefficients from autocorrelation data.
119 */
120static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order,
121                                     LPC_TYPE *ref, LPC_TYPE *error)
122{
123    int i, j;
124    LPC_TYPE err;
125    LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER];
126
127    for (i = 0; i < max_order; i++)
128        gen0[i] = gen1[i] = autoc[i + 1];
129
130    err    = autoc[0];
131    ref[0] = -gen1[0] / err;
132    err   +=  gen1[0] * ref[0];
133    if (error)
134        error[0] = err;
135    for (i = 1; i < max_order; i++) {
136        for (j = 0; j < max_order - i; j++) {
137            gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j];
138            gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j];
139        }
140        ref[i] = -gen1[0] / err;
141        err   +=  gen1[0] * ref[i];
142        if (error)
143            error[i] = err;
144    }
145}
146
147/**
148 * Levinson-Durbin recursion.
149 * Produce LPC coefficients from autocorrelation data.
150 */
151static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
152                                    LPC_TYPE *lpc, int lpc_stride, int fail,
153                                    int normalize)
154{
155    int i, j;
156    LPC_TYPE err;
157    LPC_TYPE *lpc_last = lpc;
158
159    av_assert2(normalize || !fail);
160
161    if (normalize)
162        err = *autoc++;
163
164    if (fail && (autoc[max_order - 1] == 0 || err <= 0))
165        return -1;
166
167    for(i=0; i<max_order; i++) {
168        LPC_TYPE r = -autoc[i];
169
170        if (normalize) {
171            for(j=0; j<i; j++)
172                r -= lpc_last[j] * autoc[i-j-1];
173
174            r /= err;
175            err *= 1.0 - (r * r);
176        }
177
178        lpc[i] = r;
179
180        for(j=0; j < (i+1)>>1; j++) {
181            LPC_TYPE f = lpc_last[    j];
182            LPC_TYPE b = lpc_last[i-1-j];
183            lpc[    j] = f + r * b;
184            lpc[i-1-j] = b + r * f;
185        }
186
187        if (fail && err < 0)
188            return -1;
189
190        lpc_last = lpc;
191        lpc += lpc_stride;
192    }
193
194    return 0;
195}
196
197#endif /* AVCODEC_LPC_H */
198