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lpc.h
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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 #include "libavutil/lls.h"
28 
29 #define ORDER_METHOD_EST 0
30 #define ORDER_METHOD_2LEVEL 1
31 #define ORDER_METHOD_4LEVEL 2
32 #define ORDER_METHOD_8LEVEL 3
33 #define ORDER_METHOD_SEARCH 4
34 #define ORDER_METHOD_LOG 5
35 
36 #define MIN_LPC_ORDER 1
37 #define MAX_LPC_ORDER 32
38 
39 /**
40  * LPC analysis type
41  */
42 enum FFLPCType {
43  FF_LPC_TYPE_DEFAULT = -1, ///< use the codec default LPC type
44  FF_LPC_TYPE_NONE = 0, ///< do not use LPC prediction or use all zero coefficients
45  FF_LPC_TYPE_FIXED = 1, ///< fixed LPC coefficients
46  FF_LPC_TYPE_LEVINSON = 2, ///< Levinson-Durbin recursion
47  FF_LPC_TYPE_CHOLESKY = 3, ///< Cholesky factorization
48  FF_LPC_TYPE_NB , ///< Not part of ABI
49 };
50 
51 typedef struct LPCContext {
52  int blocksize;
53  int max_order;
55  double *windowed_buffer;
57 
58  /**
59  * Apply a Welch window to an array of input samples.
60  * The output samples have the same scale as the input, but are in double
61  * sample format.
62  * @param data input samples
63  * @param len number of input samples
64  * @param w_data output samples
65  */
67  double *w_data);
68  /**
69  * Perform autocorrelation on input samples with delay of 0 to lag.
70  * @param data input samples.
71  * constraints: no alignment needed, but must have at
72  * least lag*sizeof(double) valid bytes preceding it, and
73  * size must be at least (len+1)*sizeof(double) if data is
74  * 16-byte aligned or (len+2)*sizeof(double) if data is
75  * unaligned.
76  * @param len number of input samples to process
77  * @param lag maximum delay to calculate
78  * @param autoc output autocorrelation coefficients.
79  * constraints: array size must be at least lag+1.
80  */
81  void (*lpc_compute_autocorr)(const double *data, int len, int lag,
82  double *autoc);
83 
84  // TODO: these should be allocated to reduce ABI compatibility issues
86 } LPCContext;
87 
88 
89 /**
90  * Calculate LPC coefficients for multiple orders
91  */
93  const int32_t *samples, int blocksize, int min_order,
94  int max_order, int precision,
95  int32_t coefs[][MAX_LPC_ORDER], int *shift,
96  enum FFLPCType lpc_type, int lpc_passes,
97  int omethod, int max_shift, int zero_shift);
98 
100  const int32_t *samples, int order, double *ref);
101 
102 /**
103  * Initialize LPCContext.
104  */
105 int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
106  enum FFLPCType lpc_type);
108 
109 /**
110  * Uninitialize LPCContext.
111  */
112 void ff_lpc_end(LPCContext *s);
113 
114 #ifdef LPC_USE_DOUBLE
115 #define LPC_TYPE double
116 #else
117 #define LPC_TYPE float
118 #endif
119 
120 /**
121  * Schur recursion.
122  * Produces reflection coefficients from autocorrelation data.
123  */
124 static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order,
125  LPC_TYPE *ref, LPC_TYPE *error)
126 {
127  int i, j;
128  LPC_TYPE err;
129  LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER];
130 
131  for (i = 0; i < max_order; i++)
132  gen0[i] = gen1[i] = autoc[i + 1];
133 
134  err = autoc[0];
135  ref[0] = -gen1[0] / err;
136  err += gen1[0] * ref[0];
137  if (error)
138  error[0] = err;
139  for (i = 1; i < max_order; i++) {
140  for (j = 0; j < max_order - i; j++) {
141  gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j];
142  gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j];
143  }
144  ref[i] = -gen1[0] / err;
145  err += gen1[0] * ref[i];
146  if (error)
147  error[i] = err;
148  }
149 }
150 
151 /**
152  * Levinson-Durbin recursion.
153  * Produce LPC coefficients from autocorrelation data.
154  */
155 static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
156  LPC_TYPE *lpc, int lpc_stride, int fail,
157  int normalize)
158 {
159  int i, j;
160  LPC_TYPE err = 0;
161  LPC_TYPE *lpc_last = lpc;
162 
163  av_assert2(normalize || !fail);
164 
165  if (normalize)
166  err = *autoc++;
167 
168  if (fail && (autoc[max_order - 1] == 0 || err <= 0))
169  return -1;
170 
171  for(i=0; i<max_order; i++) {
172  LPC_TYPE r = -autoc[i];
173 
174  if (normalize) {
175  for(j=0; j<i; j++)
176  r -= lpc_last[j] * autoc[i-j-1];
177 
178  r /= err;
179  err *= 1.0 - (r * r);
180  }
181 
182  lpc[i] = r;
183 
184  for(j=0; j < (i+1)>>1; j++) {
185  LPC_TYPE f = lpc_last[ j];
186  LPC_TYPE b = lpc_last[i-1-j];
187  lpc[ j] = f + r * b;
188  lpc[i-1-j] = b + r * f;
189  }
190 
191  if (fail && err < 0)
192  return -1;
193 
194  lpc_last = lpc;
195  lpc += lpc_stride;
196  }
197 
198  return 0;
199 }
200 
201 #endif /* AVCODEC_LPC_H */