/**
  * LPC utility code

  * Copyright (c) 2006  Justin Ruggles <justin.ruggles@gmail.com>

  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 

 #ifndef AVCODEC_LPC_H
 #define AVCODEC_LPC_H

 #include <stdint.h>
 #include "dsputil.h"

 
 #define ORDER_METHOD_EST     0
 #define ORDER_METHOD_2LEVEL  1
 #define ORDER_METHOD_4LEVEL  2
 #define ORDER_METHOD_8LEVEL  3
 #define ORDER_METHOD_SEARCH  4
 #define ORDER_METHOD_LOG     5
 

 #define MIN_LPC_ORDER        1
 #define MAX_LPC_ORDER       32

 
 
 /**
  * Calculate LPC coefficients for multiple orders
  */
 int ff_lpc_calc_coefs(DSPContext *s,

                       const int32_t *samples, int blocksize, int min_order,
                       int max_order, int precision,
                       int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
                       int omethod, int max_shift, int zero_shift);

 #ifdef LPC_USE_DOUBLE

 #define LPC_TYPE double

 #else

 #define LPC_TYPE float

 #endif
 
 /**
  * Levinson-Durbin recursion.
  * Produces LPC coefficients from autocorrelation data.
  */

 static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
                                     LPC_TYPE *lpc, int lpc_stride, int fail,

                                     int normalize)
 {
     int i, j;

     LPC_TYPE err;
     LPC_TYPE *lpc_last = lpc;

 
     if (normalize)
         err = *autoc++;
 
     if (fail && (autoc[max_order - 1] == 0 || err <= 0))
         return -1;
 
     for(i=0; i<max_order; i++) {

         LPC_TYPE r = -autoc[i];

 
         if (normalize) {
             for(j=0; j<i; j++)
                 r -= lpc_last[j] * autoc[i-j-1];
 
             r /= err;
             err *= 1.0 - (r * r);
         }
 
         lpc[i] = r;
 
         for(j=0; j < (i+1)>>1; j++) {

             LPC_TYPE f = lpc_last[    j];
             LPC_TYPE b = lpc_last[i-1-j];

             lpc[    j] = f + r * b;
             lpc[i-1-j] = b + r * f;
         }
 
         if (fail && err < 0)
             return -1;
 
         lpc_last = lpc;
         lpc += lpc_stride;
     }
 
     return 0;
 }
 

 #endif /* AVCODEC_LPC_H */