/*

  * 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 "libavutil/avassert.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

 /**
  * LPC analysis type
  */
 enum FFLPCType {
     FF_LPC_TYPE_DEFAULT     = -1, ///< use the codec default LPC type
     FF_LPC_TYPE_NONE        =  0, ///< do not use LPC prediction or use all zero coefficients
     FF_LPC_TYPE_FIXED       =  1, ///< fixed LPC coefficients
     FF_LPC_TYPE_LEVINSON    =  2, ///< Levinson-Durbin recursion
     FF_LPC_TYPE_CHOLESKY    =  3, ///< Cholesky factorization
     FF_LPC_TYPE_NB              , ///< Not part of ABI
 };

 typedef struct LPCContext {

     int blocksize;
     int max_order;

     enum FFLPCType lpc_type;

     double *windowed_buffer;

     double *windowed_samples;
 
     /**
      * Apply a Welch window to an array of input samples.
      * The output samples have the same scale as the input, but are in double
      * sample format.
      * @param data    input samples
      * @param len     number of input samples
      * @param w_data  output samples
      */
     void (*lpc_apply_welch_window)(const int32_t *data, int len,
                                    double *w_data);

     /**
      * Perform autocorrelation on input samples with delay of 0 to lag.
      * @param data  input samples.

      *              constraints: no alignment needed, but must have at

      *              least lag*sizeof(double) valid bytes preceding it, and

      *              size must be at least (len+1)*sizeof(double) if data is
      *              16-byte aligned or (len+2)*sizeof(double) if data is
      *              unaligned.

      * @param len   number of input samples to process
      * @param lag   maximum delay to calculate
      * @param autoc output autocorrelation coefficients.
      *              constraints: array size must be at least lag+1.
      */

     void (*lpc_compute_autocorr)(const double *data, int len, int lag,

                                  double *autoc);
 } LPCContext;
 
 

 /**
  * Calculate LPC coefficients for multiple orders
  */

 int ff_lpc_calc_coefs(LPCContext *s,

                       const int32_t *samples, int blocksize, int min_order,
                       int max_order, int precision,

                       int32_t coefs[][MAX_LPC_ORDER], int *shift,

                       enum FFLPCType lpc_type, int lpc_passes,

                       int omethod, int max_shift, int zero_shift);

 int ff_lpc_calc_ref_coefs(LPCContext *s,
                           const int32_t *samples, int order, double *ref);
 

 /**
  * Initialize LPCContext.
  */

 int ff_lpc_init(LPCContext *s, int blocksize, int max_order,

                 enum FFLPCType lpc_type);

 void ff_lpc_init_x86(LPCContext *s);

 /**
  * Uninitialize LPCContext.
  */
 void ff_lpc_end(LPCContext *s);
 

 #ifdef LPC_USE_DOUBLE

 #define LPC_TYPE double

 #else

 #define LPC_TYPE float

 #endif
 
 /**

  * Schur recursion.
  * Produces reflection coefficients from autocorrelation data.
  */
 static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order,
                                      LPC_TYPE *ref, LPC_TYPE *error)
 {
     int i, j;
     LPC_TYPE err;
     LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER];
 
     for (i = 0; i < max_order; i++)
         gen0[i] = gen1[i] = autoc[i + 1];
 
     err    = autoc[0];
     ref[0] = -gen1[0] / err;
     err   +=  gen1[0] * ref[0];
     if (error)
         error[0] = err;
     for (i = 1; i < max_order; i++) {
         for (j = 0; j < max_order - i; j++) {
             gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j];
             gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j];
         }
         ref[i] = -gen1[0] / err;
         err   +=  gen1[0] * ref[i];
         if (error)
             error[i] = err;
     }
 }
 
 /**

  * Levinson-Durbin recursion.

  * Produce 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;

     av_assert2(normalize || !fail);
 

     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 */