FFmpeg/libavcodec/lpc.h

/*
 * 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>

#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_buffer;
    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 preceding 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);

int ff_lpc_calc_ref_coefs(LPCContext *s,
                          const int32_t *samples, int order, double *ref);

/**
 * 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

/**
 * Schur recursion.
 * Produces reflection coefficients from autocorrelation data.
 */
static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order,
                                     LPC_TYPE *ref, LPC_TYPE *error)
{
    int i, j;
    LPC_TYPE err;
    LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER];

    for (i = 0; i < max_order; i++)
        gen0[i] = gen1[i] = autoc[i + 1];

    err    = autoc[0];
    ref[0] = -gen1[0] / err;
    err   +=  gen1[0] * ref[0];
    if (error)
        error[0] = err;
    for (i = 1; i < max_order; i++) {
        for (j = 0; j < max_order - i; j++) {
            gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j];
            gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j];
        }
        ref[i] = -gen1[0] / err;
        err   +=  gen1[0] * ref[i];
        if (error)
            error[i] = err;
    }
}

/**
 * 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 = 0;
    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 */