libavcodec/lpc.h

   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  */
  41 enum 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
  50 typedef 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  */
  87 int 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  */
  97 int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
  98                 enum FFLPCType lpc_type);
  99 void ff_lpc_init_x86(LPCContext *s);
 100
 101 /**
 102  * Uninitialize LPCContext.
 103  */
 104 void 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  */
 116 static 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 */