PeerStreamer

/**

 * LPC utility code

 * Copyright (c) 2006  Justin Ruggles <jruggle@earthlink.net>

 *

 * 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

 */

#include "libavutil/lls.h"

#include "dsputil.h"

#include "lpc.h"

/**

 * Levinson-Durbin recursion.

 * Produces LPC coefficients from autocorrelation data.

 */

static void compute_lpc_coefs(const double *autoc, int max_order,

                              double lpc[][MAX_LPC_ORDER], double *ref)

{

   int i, j, i2;

   double r, err, tmp;

   double lpc_tmp[MAX_LPC_ORDER];

   for(i=0; i<max_order; i++) lpc_tmp[i] = 0;

   err = autoc[0];

   for(i=0; i<max_order; i++) {

      r = -autoc[i+1];

      for(j=0; j<i; j++) {

          r -= lpc_tmp[j] * autoc[i-j];

      }

      r /= err;

      ref[i] = fabs(r);

      err *= 1.0 - (r * r);

      i2 = (i >> 1);

      lpc_tmp[i] = r;

      for(j=0; j<i2; j++) {

         tmp = lpc_tmp[j];

         lpc_tmp[j] += r * lpc_tmp[i-1-j];

         lpc_tmp[i-1-j] += r * tmp;

      }

      if(i & 1) {

          lpc_tmp[j] += lpc_tmp[j] * r;

      }

      for(j=0; j<=i; j++) {

          lpc[i][j] = -lpc_tmp[j];

      }

   }

}

/**

 * Quantize LPC coefficients

 */

static void quantize_lpc_coefs(double *lpc_in, int order, int precision,

                               int32_t *lpc_out, int *shift, int max_shift, int zero_shift)

{

    int i;

    double cmax, error;

    int32_t qmax;

    int sh;

    /* define maximum levels */

    qmax = (1 << (precision - 1)) - 1;

    /* find maximum coefficient value */

    cmax = 0.0;

    for(i=0; i<order; i++) {

        cmax= FFMAX(cmax, fabs(lpc_in[i]));

    }

    /* if maximum value quantizes to zero, return all zeros */

    if(cmax * (1 << max_shift) < 1.0) {

        *shift = zero_shift;

        memset(lpc_out, 0, sizeof(int32_t) * order);

        return;

    }

    /* calculate level shift which scales max coeff to available bits */

    sh = max_shift;

    while((cmax * (1 << sh) > qmax) && (sh > 0)) {

        sh--;

    }

    /* since negative shift values are unsupported in decoder, scale down

       coefficients instead */

    if(sh == 0 && cmax > qmax) {

        double scale = ((double)qmax) / cmax;

        for(i=0; i<order; i++) {

            lpc_in[i] *= scale;

        }

    }

    /* output quantized coefficients and level shift */

    error=0;

    for(i=0; i<order; i++) {

        error += lpc_in[i] * (1 << sh);

        lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);

        error -= lpc_out[i];

    }

    *shift = sh;

}

static int estimate_best_order(double *ref, int max_order)

{

    int i, est;

    est = 1;

    for(i=max_order-1; i>=0; i--) {

        if(ref[i] > 0.10) {

            est = i+1;

            break;

        }

    }

    return est;

}

/**

 * Calculate LPC coefficients for multiple orders

 */

int ff_lpc_calc_coefs(DSPContext *s,

                      const int32_t *samples, int blocksize, int max_order,

                      int precision, int32_t coefs[][MAX_LPC_ORDER],

                      int *shift, int use_lpc, int omethod, int max_shift, int zero_shift)

{

    double autoc[MAX_LPC_ORDER+1];

    double ref[MAX_LPC_ORDER];

    double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];

    int i, j, pass;

    int opt_order;

    assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);

    if(use_lpc == 1){

        s->flac_compute_autocorr(samples, blocksize, max_order, autoc);

        compute_lpc_coefs(autoc, max_order, lpc, ref);

    }else{

        LLSModel m[2];

        double var[MAX_LPC_ORDER+1], weight;

        for(pass=0; pass<use_lpc-1; pass++){

            av_init_lls(&m[pass&1], max_order);

            weight=0;

            for(i=max_order; i<blocksize; i++){

                for(j=0; j<=max_order; j++)

                    var[j]= samples[i-j];

                if(pass){

                    double eval, inv, rinv;

                    eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);

                    eval= (512>>pass) + fabs(eval - var[0]);

                    inv = 1/eval;

                    rinv = sqrt(inv);

                    for(j=0; j<=max_order; j++)

                        var[j] *= rinv;

                    weight += inv;

                }else

                    weight++;

                av_update_lls(&m[pass&1], var, 1.0);

            }

            av_solve_lls(&m[pass&1], 0.001, 0);

        }

        for(i=0; i<max_order; i++){

            for(j=0; j<max_order; j++)

                lpc[i][j]= m[(pass-1)&1].coeff[i][j];

            ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;

        }

        for(i=max_order-1; i>0; i--)

            ref[i] = ref[i-1] - ref[i];

    }

    opt_order = max_order;

    if(omethod == ORDER_METHOD_EST) {

        opt_order = estimate_best_order(ref, max_order);

        i = opt_order-1;

        quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);

    } else {

        for(i=0; i<max_order; i++) {

            quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);

        }

    }

    return opt_order;

}