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/*
* LPC utility functions
* 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_FUNCTIONS_H
#define AVCODEC_LPC_FUNCTIONS_H
#include "libavutil/avassert.h"
#ifndef LPC_USE_FIXED
#define LPC_USE_FIXED 0
#endif
#if LPC_USE_FIXED
typedef int LPC_TYPE;
typedef unsigned LPC_TYPE_U;
#else
#ifndef LPC_SRA_R
#define LPC_SRA_R(x, y) (x)
#define LPC_MUL26(x, y) ((x) * (y))
#define LPC_FIXR(x) ((float)(x))
#endif
#ifdef LPC_USE_DOUBLE
typedef double LPC_TYPE;
typedef double LPC_TYPE_U;
#else
typedef float LPC_TYPE;
typedef float LPC_TYPE_U;
#endif
#endif // USE_FIXED
/**
* 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)
{
LPC_TYPE err = 0;
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(int i = 0; i < max_order; i++) {
LPC_TYPE r = LPC_SRA_R(-autoc[i], 5);
if (normalize) {
for(int j = 0; j < i; j++)
r -= lpc_last[j] * autoc[i-j-1];
if (err)
r /= err;
err *= LPC_FIXR(1.0) - (r * r);
}
lpc[i] = r;
for(int j = 0; j < (i + 1) >> 1; j++) {
LPC_TYPE f = lpc_last[ j];
LPC_TYPE b = lpc_last[i-1-j];
lpc[ j] = f + (LPC_TYPE_U)LPC_MUL26(r, b);
lpc[i-1-j] = b + (LPC_TYPE_U)LPC_MUL26(r, f);
}
if (fail && err < 0)
return -1;
lpc_last = lpc;
lpc += lpc_stride;
}
return 0;
}
#endif /* AVCODEC_LPC_FUNCTIONS_H */
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