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101 lines
2.6 KiB
C
101 lines
2.6 KiB
C
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/*
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* LPC utility functions
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* Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef AVCODEC_LPC_FUNCTIONS_H
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#define AVCODEC_LPC_FUNCTIONS_H
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#include "libavutil/avassert.h"
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#ifndef LPC_USE_FIXED
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#define LPC_USE_FIXED 0
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#endif
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#if LPC_USE_FIXED
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typedef int LPC_TYPE;
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typedef unsigned LPC_TYPE_U;
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#else
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#ifndef LPC_SRA_R
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#define LPC_SRA_R(x, y) (x)
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#define LPC_MUL26(x, y) ((x) * (y))
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#define LPC_FIXR(x) ((float)(x))
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#endif
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#ifdef LPC_USE_DOUBLE
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typedef double LPC_TYPE;
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typedef double LPC_TYPE_U;
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#else
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typedef float LPC_TYPE;
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typedef float LPC_TYPE_U;
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#endif
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#endif // USE_FIXED
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/**
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* Levinson-Durbin recursion.
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* Produce LPC coefficients from autocorrelation data.
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*/
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static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
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LPC_TYPE *lpc, int lpc_stride, int fail,
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int normalize)
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{
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LPC_TYPE err = 0;
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LPC_TYPE *lpc_last = lpc;
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av_assert2(normalize || !fail);
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if (normalize)
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err = *autoc++;
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if (fail && (autoc[max_order - 1] == 0 || err <= 0))
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return -1;
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for(int i = 0; i < max_order; i++) {
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LPC_TYPE r = LPC_SRA_R(-autoc[i], 5);
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if (normalize) {
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for(int j = 0; j < i; j++)
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r -= lpc_last[j] * autoc[i-j-1];
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if (err)
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r /= err;
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err *= LPC_FIXR(1.0) - (r * r);
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}
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lpc[i] = r;
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for(int j = 0; j < (i + 1) >> 1; j++) {
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LPC_TYPE f = lpc_last[ j];
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LPC_TYPE b = lpc_last[i-1-j];
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lpc[ j] = f + (LPC_TYPE_U)LPC_MUL26(r, b);
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lpc[i-1-j] = b + (LPC_TYPE_U)LPC_MUL26(r, f);
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}
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if (fail && err < 0)
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return -1;
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lpc_last = lpc;
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lpc += lpc_stride;
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}
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return 0;
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}
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#endif /* AVCODEC_LPC_FUNCTIONS_H */
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