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/**
* LPC utility code
* Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; 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
/**
* 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_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 have at
* least lag*sizeof(double) valid bytes preceeding 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);
/**
* 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
/**
* 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;
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 */
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