PeerStreamer

/**

 * 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 "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

typedef struct LPCContext {

    int blocksize;

    int max_order;

    enum AVLPCType 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 AVLPCType 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 AVLPCType 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 */