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ffmpeg / libavcodec / lpc.c @ 1be0fc29

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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 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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#include "libavutil/lls.h"
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#include "dsputil.h"
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#define LPC_USE_DOUBLE
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#include "lpc.h"
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/**
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 * Quantize LPC coefficients
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 */
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static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
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                               int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
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{
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    int i;
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    double cmax, error;
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    int32_t qmax;
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    int sh;
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    /* define maximum levels */
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    qmax = (1 << (precision - 1)) - 1;
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    /* find maximum coefficient value */
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    cmax = 0.0;
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    for(i=0; i<order; i++) {
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        cmax= FFMAX(cmax, fabs(lpc_in[i]));
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    }
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    /* if maximum value quantizes to zero, return all zeros */
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    if(cmax * (1 << max_shift) < 1.0) {
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        *shift = zero_shift;
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        memset(lpc_out, 0, sizeof(int32_t) * order);
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        return;
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    }
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    /* calculate level shift which scales max coeff to available bits */
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    sh = max_shift;
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    while((cmax * (1 << sh) > qmax) && (sh > 0)) {
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        sh--;
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    }
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    /* since negative shift values are unsupported in decoder, scale down
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       coefficients instead */
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    if(sh == 0 && cmax > qmax) {
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        double scale = ((double)qmax) / cmax;
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        for(i=0; i<order; i++) {
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            lpc_in[i] *= scale;
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        }
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    }
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    /* output quantized coefficients and level shift */
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    error=0;
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    for(i=0; i<order; i++) {
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        error -= lpc_in[i] * (1 << sh);
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        lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
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        error -= lpc_out[i];
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    }
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    *shift = sh;
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}
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static int estimate_best_order(double *ref, int min_order, int max_order)
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{
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    int i, est;
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    est = min_order;
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    for(i=max_order-1; i>=min_order-1; i--) {
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        if(ref[i] > 0.10) {
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            est = i+1;
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            break;
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        }
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    }
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    return est;
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}
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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(DSPContext *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, int use_lpc,
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                      int omethod, int max_shift, int zero_shift)
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{
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    double autoc[MAX_LPC_ORDER+1];
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    double ref[MAX_LPC_ORDER];
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    double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
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    int i, j, pass;
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    int opt_order;
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    assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);
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    if(use_lpc == 1){
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        s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
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        compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
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        for(i=0; i<max_order; i++)
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            ref[i] = fabs(lpc[i][i]);
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    }else{
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        LLSModel m[2];
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        double var[MAX_LPC_ORDER+1], weight;
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        for(pass=0; pass<use_lpc-1; pass++){
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            av_init_lls(&m[pass&1], max_order);
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            weight=0;
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            for(i=max_order; i<blocksize; i++){
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                for(j=0; j<=max_order; j++)
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                    var[j]= samples[i-j];
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                if(pass){
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                    double eval, inv, rinv;
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                    eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
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                    eval= (512>>pass) + fabs(eval - var[0]);
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                    inv = 1/eval;
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                    rinv = sqrt(inv);
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                    for(j=0; j<=max_order; j++)
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                        var[j] *= rinv;
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                    weight += inv;
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                }else
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                    weight++;
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                av_update_lls(&m[pass&1], var, 1.0);
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            }
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            av_solve_lls(&m[pass&1], 0.001, 0);
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        }
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        for(i=0; i<max_order; i++){
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            for(j=0; j<max_order; j++)
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                lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
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            ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
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        }
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        for(i=max_order-1; i>0; i--)
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            ref[i] = ref[i-1] - ref[i];
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    }
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    opt_order = max_order;
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    if(omethod == ORDER_METHOD_EST) {
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        opt_order = estimate_best_order(ref, min_order, max_order);
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        i = opt_order-1;
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        quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
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    } else {
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        for(i=min_order-1; i<max_order; i++) {
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            quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
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        }
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    }
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    return opt_order;
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}