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/**
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 * LPC utility code
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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 Libav.
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 *
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 * Libav 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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 * Libav 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 Libav; 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_H
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#define AVCODEC_LPC_H
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#include <stdint.h>
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#include "dsputil.h"
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#define ORDER_METHOD_EST     0
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#define ORDER_METHOD_2LEVEL  1
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#define ORDER_METHOD_4LEVEL  2
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#define ORDER_METHOD_8LEVEL  3
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#define ORDER_METHOD_SEARCH  4
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#define ORDER_METHOD_LOG     5
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#define MIN_LPC_ORDER        1
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#define MAX_LPC_ORDER       32
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typedef struct LPCContext {
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    int blocksize;
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    int max_order;
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    enum AVLPCType lpc_type;
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    double *windowed_samples;
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    /**
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     * Apply a Welch window to an array of input samples.
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     * The output samples have the same scale as the input, but are in double
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     * sample format.
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     * @param data    input samples
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     * @param len     number of input samples
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     * @param w_data  output samples
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     */
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    void (*lpc_apply_welch_window)(const int32_t *data, int len,
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                                   double *w_data);
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    /**
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     * Perform autocorrelation on input samples with delay of 0 to lag.
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     * @param data  input samples.
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     *              constraints: no alignment needed, but must have have at
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     *              least lag*sizeof(double) valid bytes preceeding it, and
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     *              size must be at least (len+1)*sizeof(double) if data is
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     *              16-byte aligned or (len+2)*sizeof(double) if data is
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     *              unaligned.
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     * @param len   number of input samples to process
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     * @param lag   maximum delay to calculate
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     * @param autoc output autocorrelation coefficients.
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     *              constraints: array size must be at least lag+1.
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     */
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    void (*lpc_compute_autocorr)(const double *data, int len, int lag,
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                                 double *autoc);
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} LPCContext;
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/**
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 * Calculate LPC coefficients for multiple orders
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 */
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int ff_lpc_calc_coefs(LPCContext *s,
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                      const int32_t *samples, int blocksize, int min_order,
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                      int max_order, int precision,
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                      int32_t coefs[][MAX_LPC_ORDER], int *shift,
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                      enum AVLPCType lpc_type, int lpc_passes,
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                      int omethod, int max_shift, int zero_shift);
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/**
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 * Initialize LPCContext.
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 */
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int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
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                enum AVLPCType lpc_type);
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void ff_lpc_init_x86(LPCContext *s);
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/**
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 * Uninitialize LPCContext.
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 */
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void ff_lpc_end(LPCContext *s);
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#ifdef LPC_USE_DOUBLE
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#define LPC_TYPE double
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#else
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#define LPC_TYPE float
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#endif
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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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    int i, j;
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    LPC_TYPE err;
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    LPC_TYPE *lpc_last = lpc;
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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(i=0; i<max_order; i++) {
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        LPC_TYPE r = -autoc[i];
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        if (normalize) {
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            for(j=0; j<i; j++)
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                r -= lpc_last[j] * autoc[i-j-1];
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            r /= err;
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            err *= 1.0 - (r * r);
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        }
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        lpc[i] = r;
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        for(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 + r * b;
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            lpc[i-1-j] = b + 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_H */