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 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  */
  42 int 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
  48 #ifdef LPC_USE_DOUBLE
  49 #define LPC_TYPE double
  50 #else
  51 #define LPC_TYPE float
  52 #endif
  53
  54 /**
  55  * Levinson-Durbin recursion.
  56  * Produces LPC coefficients from autocorrelation data.
  57  */
  58 static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
  59                                     LPC_TYPE *lpc, int lpc_stride, int fail,
  60                                     int normalize)
  61 {
  62     int i, j;
  63     LPC_TYPE err;
  64     LPC_TYPE *lpc_last = lpc;
  65
  66     if (normalize)
  67         err = *autoc++;
  68
  69     if (fail && (autoc[max_order - 1] == 0 || err <= 0))
  70         return -1;
  71
  72     for(i=0; i<max_order; i++) {
  73         LPC_TYPE r = -autoc[i];
  74
  75         if (normalize) {
  76             for(j=0; j<i; j++)
  77                 r -= lpc_last[j] * autoc[i-j-1];
  78
  79             r /= err;
  80             err *= 1.0 - (r * r);
  81         }
  82
  83         lpc[i] = r;
  84
  85         for(j=0; j < (i+1)>>1; j++) {
  86             LPC_TYPE f = lpc_last[    j];
  87             LPC_TYPE b = lpc_last[i-1-j];
  88             lpc[    j] = f + r * b;
  89             lpc[i-1-j] = b + r * f;
  90         }
  91
  92         if (fail && err < 0)
  93             return -1;
  94
  95         lpc_last = lpc;
  96         lpc += lpc_stride;
  97     }
  98
  99     return 0;
 100 }
 101
 102 #endif /* AVCODEC_LPC_H */