flacenc.c

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/**
 * FLAC audio encoder
 * 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/crc.h"
#include "libavutil/lls.h"
#include "avcodec.h"
#include "bitstream.h"
#include "dsputil.h"
#include "golomb.h"

#define FLAC_MAX_CH  8
#define FLAC_MIN_BLOCKSIZE  16
#define FLAC_MAX_BLOCKSIZE  65535

#define FLAC_SUBFRAME_CONSTANT  0
#define FLAC_SUBFRAME_VERBATIM  1
#define FLAC_SUBFRAME_FIXED     8
#define FLAC_SUBFRAME_LPC      32

#define FLAC_CHMODE_NOT_STEREO      0
#define FLAC_CHMODE_LEFT_RIGHT      1
#define FLAC_CHMODE_LEFT_SIDE       8
#define FLAC_CHMODE_RIGHT_SIDE      9
#define FLAC_CHMODE_MID_SIDE       10

#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 FLAC_STREAMINFO_SIZE  34

#define MIN_LPC_ORDER       1
#define MAX_LPC_ORDER      32
#define MAX_FIXED_ORDER     4
#define MAX_PARTITION_ORDER 8
#define MAX_PARTITIONS     (1 << MAX_PARTITION_ORDER)
#define MAX_LPC_PRECISION  15
#define MAX_LPC_SHIFT      15
#define MAX_RICE_PARAM     14

typedef struct CompressionOptions {
    int compression_level;
    int block_time_ms;
    int use_lpc;
    int lpc_coeff_precision;
    int min_prediction_order;
    int max_prediction_order;
    int prediction_order_method;
    int min_partition_order;
    int max_partition_order;
} CompressionOptions;

typedef struct RiceContext {
    int porder;
    int params[MAX_PARTITIONS];
} RiceContext;

typedef struct FlacSubframe {
    int type;
    int type_code;
    int obits;
    int order;
    int32_t coefs[MAX_LPC_ORDER];
    int shift;
    RiceContext rc;
    int32_t samples[FLAC_MAX_BLOCKSIZE];
    int32_t residual[FLAC_MAX_BLOCKSIZE+1];
} FlacSubframe;

typedef struct FlacFrame {
    FlacSubframe subframes[FLAC_MAX_CH];
    int blocksize;
    int bs_code[2];
    uint8_t crc8;
    int ch_mode;
} FlacFrame;

typedef struct FlacEncodeContext {
    PutBitContext pb;
    int channels;
    int ch_code;
    int samplerate;
    int sr_code[2];
    int max_framesize;
    uint32_t frame_count;
    FlacFrame frame;
    CompressionOptions options;
    AVCodecContext *avctx;
    DSPContext dsp;
} FlacEncodeContext;

static const int flac_samplerates[16] = {
    0, 0, 0, 0,
    8000, 16000, 22050, 24000, 32000, 44100, 48000, 96000,
    0, 0, 0, 0
};

static const int flac_blocksizes[16] = {
    0,
    192,
    576, 1152, 2304, 4608,
    0, 0,
    256, 512, 1024, 2048, 4096, 8192, 16384, 32768
};

/**
 * Writes streaminfo metadata block to byte array
 */
static void write_streaminfo(FlacEncodeContext *s, uint8_t *header)
{
    PutBitContext pb;

    memset(header, 0, FLAC_STREAMINFO_SIZE);
    init_put_bits(&pb, header, FLAC_STREAMINFO_SIZE);

    /* streaminfo metadata block */
    put_bits(&pb, 16, s->avctx->frame_size);
    put_bits(&pb, 16, s->avctx->frame_size);
    put_bits(&pb, 24, 0);
    put_bits(&pb, 24, s->max_framesize);
    put_bits(&pb, 20, s->samplerate);
    put_bits(&pb, 3, s->channels-1);
    put_bits(&pb, 5, 15);       /* bits per sample - 1 */
    flush_put_bits(&pb);
    /* total samples = 0 */
    /* MD5 signature = 0 */
}

/**
 * Sets blocksize based on samplerate
 * Chooses the closest predefined blocksize >= BLOCK_TIME_MS milliseconds
 */
static int select_blocksize(int samplerate, int block_time_ms)
{
    int i;
    int target;
    int blocksize;

    assert(samplerate > 0);
    blocksize = flac_blocksizes[1];
    target = (samplerate * block_time_ms) / 1000;
    for(i=0; i<16; i++) {
        if(target >= flac_blocksizes[i] && flac_blocksizes[i] > blocksize) {
            blocksize = flac_blocksizes[i];
        }
    }
    return blocksize;
}

static av_cold int flac_encode_init(AVCodecContext *avctx)
{
    int freq = avctx->sample_rate;
    int channels = avctx->channels;
    FlacEncodeContext *s = avctx->priv_data;
    int i, level;
    uint8_t *streaminfo;

    s->avctx = avctx;

    dsputil_init(&s->dsp, avctx);

    if(avctx->sample_fmt != SAMPLE_FMT_S16) {
        return -1;
    }

    if(channels < 1 || channels > FLAC_MAX_CH) {
        return -1;
    }
    s->channels = channels;
    s->ch_code = s->channels-1;

    /* find samplerate in table */
    if(freq < 1)
        return -1;
    for(i=4; i<12; i++) {
        if(freq == flac_samplerates[i]) {
            s->samplerate = flac_samplerates[i];
            s->sr_code[0] = i;
            s->sr_code[1] = 0;
            break;
        }
    }
    /* if not in table, samplerate is non-standard */
    if(i == 12) {
        if(freq % 1000 == 0 && freq < 255000) {
            s->sr_code[0] = 12;
            s->sr_code[1] = freq / 1000;
        } else if(freq % 10 == 0 && freq < 655350) {
            s->sr_code[0] = 14;
            s->sr_code[1] = freq / 10;
        } else if(freq < 65535) {
            s->sr_code[0] = 13;
            s->sr_code[1] = freq;
        } else {
            return -1;
        }
        s->samplerate = freq;
    }

    /* set compression option defaults based on avctx->compression_level */
    if(avctx->compression_level < 0) {
        s->options.compression_level = 5;
    } else {
        s->options.compression_level = avctx->compression_level;
    }
    av_log(avctx, AV_LOG_DEBUG, " compression: %d\n", s->options.compression_level);

    level= s->options.compression_level;
    if(level > 12) {
        av_log(avctx, AV_LOG_ERROR, "invalid compression level: %d\n",
               s->options.compression_level);
        return -1;
    }

    s->options.block_time_ms       = ((int[]){ 27, 27, 27,105,105,105,105,105,105,105,105,105,105})[level];
    s->options.use_lpc             = ((int[]){  0,  0,  0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1})[level];
    s->options.min_prediction_order= ((int[]){  2,  0,  0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1})[level];
    s->options.max_prediction_order= ((int[]){  3,  4,  4,  6,  8,  8,  8,  8, 12, 12, 12, 32, 32})[level];
    s->options.prediction_order_method = ((int[]){ ORDER_METHOD_EST,    ORDER_METHOD_EST,    ORDER_METHOD_EST,
                                                   ORDER_METHOD_EST,    ORDER_METHOD_EST,    ORDER_METHOD_EST,
                                                   ORDER_METHOD_4LEVEL, ORDER_METHOD_LOG,    ORDER_METHOD_4LEVEL,
                                                   ORDER_METHOD_LOG,    ORDER_METHOD_SEARCH, ORDER_METHOD_LOG,
                                                   ORDER_METHOD_SEARCH})[level];
    s->options.min_partition_order = ((int[]){  2,  2,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0})[level];
    s->options.max_partition_order = ((int[]){  2,  2,  3,  3,  3,  8,  8,  8,  8,  8,  8,  8,  8})[level];

    /* set compression option overrides from AVCodecContext */
    if(avctx->use_lpc >= 0) {
        s->options.use_lpc = av_clip(avctx->use_lpc, 0, 11);
    }
    if(s->options.use_lpc == 1)
        av_log(avctx, AV_LOG_DEBUG, " use lpc: Levinson-Durbin recursion with Welch window\n");
    else if(s->options.use_lpc > 1)
        av_log(avctx, AV_LOG_DEBUG, " use lpc: Cholesky factorization\n");

    if(avctx->min_prediction_order >= 0) {
        if(s->options.use_lpc) {
            if(avctx->min_prediction_order < MIN_LPC_ORDER ||
                    avctx->min_prediction_order > MAX_LPC_ORDER) {
                av_log(avctx, AV_LOG_ERROR, "invalid min prediction order: %d\n",
                       avctx->min_prediction_order);
                return -1;
            }
        } else {
            if(avctx->min_prediction_order > MAX_FIXED_ORDER) {
                av_log(avctx, AV_LOG_ERROR, "invalid min prediction order: %d\n",
                       avctx->min_prediction_order);
                return -1;
            }
        }
        s->options.min_prediction_order = avctx->min_prediction_order;
    }
    if(avctx->max_prediction_order >= 0) {
        if(s->options.use_lpc) {
            if(avctx->max_prediction_order < MIN_LPC_ORDER ||
                    avctx->max_prediction_order > MAX_LPC_ORDER) {
                av_log(avctx, AV_LOG_ERROR, "invalid max prediction order: %d\n",
                       avctx->max_prediction_order);
                return -1;
            }
        } else {
            if(avctx->max_prediction_order > MAX_FIXED_ORDER) {
                av_log(avctx, AV_LOG_ERROR, "invalid max prediction order: %d\n",
                       avctx->max_prediction_order);
                return -1;
            }
        }
        s->options.max_prediction_order = avctx->max_prediction_order;
    }
    if(s->options.max_prediction_order < s->options.min_prediction_order) {
        av_log(avctx, AV_LOG_ERROR, "invalid prediction orders: min=%d max=%d\n",
               s->options.min_prediction_order, s->options.max_prediction_order);
        return -1;
    }
    av_log(avctx, AV_LOG_DEBUG, " prediction order: %d, %d\n",
           s->options.min_prediction_order, s->options.max_prediction_order);

    if(avctx->prediction_order_method >= 0) {
        if(avctx->prediction_order_method > ORDER_METHOD_LOG) {
            av_log(avctx, AV_LOG_ERROR, "invalid prediction order method: %d\n",
                   avctx->prediction_order_method);
            return -1;
        }
        s->options.prediction_order_method = avctx->prediction_order_method;
    }
    switch(s->options.prediction_order_method) {
        case ORDER_METHOD_EST:    av_log(avctx, AV_LOG_DEBUG, " order method: %s\n",
                                         "estimate"); break;
        case ORDER_METHOD_2LEVEL: av_log(avctx, AV_LOG_DEBUG, " order method: %s\n",
                                         "2-level"); break;
        case ORDER_METHOD_4LEVEL: av_log(avctx, AV_LOG_DEBUG, " order method: %s\n",
                                         "4-level"); break;
        case ORDER_METHOD_8LEVEL: av_log(avctx, AV_LOG_DEBUG, " order method: %s\n",
                                         "8-level"); break;
        case ORDER_METHOD_SEARCH: av_log(avctx, AV_LOG_DEBUG, " order method: %s\n",
                                         "full search"); break;
        case ORDER_METHOD_LOG:    av_log(avctx, AV_LOG_DEBUG, " order method: %s\n",
                                         "log search"); break;
    }

    if(avctx->min_partition_order >= 0) {
        if(avctx->min_partition_order > MAX_PARTITION_ORDER) {
            av_log(avctx, AV_LOG_ERROR, "invalid min partition order: %d\n",
                   avctx->min_partition_order);
            return -1;
        }
        s->options.min_partition_order = avctx->min_partition_order;
    }
    if(avctx->max_partition_order >= 0) {
        if(avctx->max_partition_order > MAX_PARTITION_ORDER) {
            av_log(avctx, AV_LOG_ERROR, "invalid max partition order: %d\n",
                   avctx->max_partition_order);
            return -1;
        }
        s->options.max_partition_order = avctx->max_partition_order;
    }
    if(s->options.max_partition_order < s->options.min_partition_order) {
        av_log(avctx, AV_LOG_ERROR, "invalid partition orders: min=%d max=%d\n",
               s->options.min_partition_order, s->options.max_partition_order);
        return -1;
    }
    av_log(avctx, AV_LOG_DEBUG, " partition order: %d, %d\n",
           s->options.min_partition_order, s->options.max_partition_order);

    if(avctx->frame_size > 0) {
        if(avctx->frame_size < FLAC_MIN_BLOCKSIZE ||
                avctx->frame_size > FLAC_MAX_BLOCKSIZE) {
            av_log(avctx, AV_LOG_ERROR, "invalid block size: %d\n",
                   avctx->frame_size);
            return -1;
        }
    } else {
        s->avctx->frame_size = select_blocksize(s->samplerate, s->options.block_time_ms);
    }
    av_log(avctx, AV_LOG_DEBUG, " block size: %d\n", s->avctx->frame_size);

    /* set LPC precision */
    if(avctx->lpc_coeff_precision > 0) {
        if(avctx->lpc_coeff_precision > MAX_LPC_PRECISION) {
            av_log(avctx, AV_LOG_ERROR, "invalid lpc coeff precision: %d\n",
                   avctx->lpc_coeff_precision);
            return -1;
        }
        s->options.lpc_coeff_precision = avctx->lpc_coeff_precision;
    } else {
        /* default LPC precision */
        s->options.lpc_coeff_precision = 15;
    }
    av_log(avctx, AV_LOG_DEBUG, " lpc precision: %d\n",
           s->options.lpc_coeff_precision);

    /* set maximum encoded frame size in verbatim mode */
    if(s->channels == 2) {
        s->max_framesize = 14 + ((s->avctx->frame_size * 33 + 7) >> 3);
    } else {
        s->max_framesize = 14 + (s->avctx->frame_size * s->channels * 2);
    }

    streaminfo = av_malloc(FLAC_STREAMINFO_SIZE);
    write_streaminfo(s, streaminfo);
    avctx->extradata = streaminfo;
    avctx->extradata_size = FLAC_STREAMINFO_SIZE;

    s->frame_count = 0;

    avctx->coded_frame = avcodec_alloc_frame();
    avctx->coded_frame->key_frame = 1;

    return 0;
}

static void init_frame(FlacEncodeContext *s)
{
    int i, ch;
    FlacFrame *frame;

    frame = &s->frame;

    for(i=0; i<16; i++) {
        if(s->avctx->frame_size == flac_blocksizes[i]) {
            frame->blocksize = flac_blocksizes[i];
            frame->bs_code[0] = i;
            frame->bs_code[1] = 0;
            break;
        }
    }
    if(i == 16) {
        frame->blocksize = s->avctx->frame_size;
        if(frame->blocksize <= 256) {
            frame->bs_code[0] = 6;
            frame->bs_code[1] = frame->blocksize-1;
        } else {
            frame->bs_code[0] = 7;
            frame->bs_code[1] = frame->blocksize-1;
        }
    }

    for(ch=0; ch<s->channels; ch++) {
        frame->subframes[ch].obits = 16;
    }
}

/**
 * Copy channel-interleaved input samples into separate subframes
 */
static void copy_samples(FlacEncodeContext *s, int16_t *samples)
{
    int i, j, ch;
    FlacFrame *frame;

    frame = &s->frame;
    for(i=0,j=0; i<frame->blocksize; i++) {
        for(ch=0; ch<s->channels; ch++,j++) {
            frame->subframes[ch].samples[i] = samples[j];
        }
    }
}


#define rice_encode_count(sum, n, k) (((n)*((k)+1))+((sum-(n>>1))>>(k)))

/**
 * Solve for d/dk(rice_encode_count) = n-((sum-(n>>1))>>(k+1)) = 0
 */
static int find_optimal_param(uint32_t sum, int n)
{
    int k;
    uint32_t sum2;

    if(sum <= n>>1)
        return 0;
    sum2 = sum-(n>>1);
    k = av_log2(n<256 ? FASTDIV(sum2,n) : sum2/n);
    return FFMIN(k, MAX_RICE_PARAM);
}

static uint32_t calc_optimal_rice_params(RiceContext *rc, int porder,
                                         uint32_t *sums, int n, int pred_order)
{
    int i;
    int k, cnt, part;
    uint32_t all_bits;

    part = (1 << porder);
    all_bits = 4 * part;

    cnt = (n >> porder) - pred_order;
    for(i=0; i<part; i++) {
        k = find_optimal_param(sums[i], cnt);
        rc->params[i] = k;
        all_bits += rice_encode_count(sums[i], cnt, k);
        cnt = n >> porder;
    }

    rc->porder = porder;

    return all_bits;
}

static void calc_sums(int pmin, int pmax, uint32_t *data, int n, int pred_order,
                      uint32_t sums[][MAX_PARTITIONS])
{
    int i, j;
    int parts;
    uint32_t *res, *res_end;

    /* sums for highest level */
    parts = (1 << pmax);
    res = &data[pred_order];
    res_end = &data[n >> pmax];
    for(i=0; i<parts; i++) {
        uint32_t sum = 0;
        while(res < res_end){
            sum += *(res++);
        }
        sums[pmax][i] = sum;
        res_end+= n >> pmax;
    }
    /* sums for lower levels */
    for(i=pmax-1; i>=pmin; i--) {
        parts = (1 << i);
        for(j=0; j<parts; j++) {
            sums[i][j] = sums[i+1][2*j] + sums[i+1][2*j+1];
        }
    }
}

static uint32_t calc_rice_params(RiceContext *rc, int pmin, int pmax,
                                 int32_t *data, int n, int pred_order)
{
    int i;
    uint32_t bits[MAX_PARTITION_ORDER+1];
    int opt_porder;
    RiceContext tmp_rc;
    uint32_t *udata;
    uint32_t sums[MAX_PARTITION_ORDER+1][MAX_PARTITIONS];

    assert(pmin >= 0 && pmin <= MAX_PARTITION_ORDER);
    assert(pmax >= 0 && pmax <= MAX_PARTITION_ORDER);
    assert(pmin <= pmax);

    udata = av_malloc(n * sizeof(uint32_t));
    for(i=0; i<n; i++) {
        udata[i] = (2*data[i]) ^ (data[i]>>31);
    }

    calc_sums(pmin, pmax, udata, n, pred_order, sums);

    opt_porder = pmin;
    bits[pmin] = UINT32_MAX;
    for(i=pmin; i<=pmax; i++) {
        bits[i] = calc_optimal_rice_params(&tmp_rc, i, sums[i], n, pred_order);
        if(bits[i] <= bits[opt_porder]) {
            opt_porder = i;
            *rc= tmp_rc;
        }
    }

    av_freep(&udata);
    return bits[opt_porder];
}

static int get_max_p_order(int max_porder, int n, int order)
{
    int porder = FFMIN(max_porder, av_log2(n^(n-1)));
    if(order > 0)
        porder = FFMIN(porder, av_log2(n/order));
    return porder;
}

static uint32_t calc_rice_params_fixed(RiceContext *rc, int pmin, int pmax,
                                       int32_t *data, int n, int pred_order,
                                       int bps)
{
    uint32_t bits;
    pmin = get_max_p_order(pmin, n, pred_order);
    pmax = get_max_p_order(pmax, n, pred_order);
    bits = pred_order*bps + 6;
    bits += calc_rice_params(rc, pmin, pmax, data, n, pred_order);
    return bits;
}

static uint32_t calc_rice_params_lpc(RiceContext *rc, int pmin, int pmax,
                                     int32_t *data, int n, int pred_order,
                                     int bps, int precision)
{
    uint32_t bits;
    pmin = get_max_p_order(pmin, n, pred_order);
    pmax = get_max_p_order(pmax, n, pred_order);
    bits = pred_order*bps + 4 + 5 + pred_order*precision + 6;
    bits += calc_rice_params(rc, pmin, pmax, data, n, pred_order);
    return bits;
}

/**
 * Apply Welch window function to audio block
 */
static void apply_welch_window(const int32_t *data, int len, double *w_data)
{
    int i, n2;
    double w;
    double c;

    assert(!(len&1)); //the optimization in r11881 does not support odd len
                      //if someone wants odd len extend the change in r11881

    n2 = (len >> 1);
    c = 2.0 / (len - 1.0);

    w_data+=n2;
      data+=n2;
    for(i=0; i<n2; i++) {
        w = c - n2 + i;
        w = 1.0 - (w * w);
        w_data[-i-1] = data[-i-1] * w;
        w_data[+i  ] = data[+i  ] * w;
    }
}

/**
 * Calculates autocorrelation data from audio samples
 * A Welch window function is applied before calculation.
 */
void ff_flac_compute_autocorr(const int32_t *data, int len, int lag,
                              double *autoc)
{
    int i, j;
    double tmp[len + lag + 1];
    double *data1= tmp + lag;

    apply_welch_window(data, len, data1);

    for(j=0; j<lag; j++)
        data1[j-lag]= 0.0;
    data1[len] = 0.0;

    for(j=0; j<lag; j+=2){
        double sum0 = 1.0, sum1 = 1.0;
        for(i=0; i<len; i++){
            sum0 += data1[i] * data1[i-j];
            sum1 += data1[i] * data1[i-j-1];
        }
        autoc[j  ] = sum0;
        autoc[j+1] = sum1;
    }

    if(j==lag){
        double sum = 1.0;
        for(i=0; i<len; i+=2){
            sum += data1[i  ] * data1[i-j  ]
                 + data1[i+1] * data1[i-j+1];
        }
        autoc[j] = sum;
    }
}

/**
 * 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 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_LPC_SHIFT) < 1.0) {
        *shift = 0;
        memset(lpc_out, 0, sizeof(int32_t) * order);
        return;
    }

    /* calculate level shift which scales max coeff to available bits */
    sh = MAX_LPC_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
 */
static int lpc_calc_coefs(FlacEncodeContext *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)
{
    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->dsp.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]);
    } else {
        for(i=0; i<max_order; i++) {
            quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i]);
        }
    }

    return opt_order;
}


static void encode_residual_verbatim(int32_t *res, int32_t *smp, int n)
{
    assert(n > 0);
    memcpy(res, smp, n * sizeof(int32_t));
}

static void encode_residual_fixed(int32_t *res, const int32_t *smp, int n,
                                  int order)
{
    int i;

    for(i=0; i<order; i++) {
        res[i] = smp[i];
    }

    if(order==0){
        for(i=order; i<n; i++)
            res[i]= smp[i];
    }else if(order==1){
        for(i=order; i<n; i++)
            res[i]= smp[i] - smp[i-1];
    }else if(order==2){
        int a = smp[order-1] - smp[order-2];
        for(i=order; i<n; i+=2) {
            int b = smp[i] - smp[i-1];
            res[i]= b - a;
            a = smp[i+1] - smp[i];
            res[i+1]= a - b;
        }
    }else if(order==3){
        int a = smp[order-1] - smp[order-2];
        int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
        for(i=order; i<n; i+=2) {
            int b = smp[i] - smp[i-1];
            int d = b - a;
            res[i]= d - c;
            a = smp[i+1] - smp[i];
            c = a - b;
            res[i+1]= c - d;
        }
    }else{
        int a = smp[order-1] - smp[order-2];
        int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
        int e = smp[order-1] - 3*smp[order-2] + 3*smp[order-3] - smp[order-4];
        for(i=order; i<n; i+=2) {
            int b = smp[i] - smp[i-1];
            int d = b - a;
            int f = d - c;
            res[i]= f - e;
            a = smp[i+1] - smp[i];
            c = a - b;
            e = c - d;
            res[i+1]= e - f;
        }
    }
}

#define LPC1(x) {\
    int c = coefs[(x)-1];\
    p0 += c*s;\
    s = smp[i-(x)+1];\
    p1 += c*s;\
}

static av_always_inline void encode_residual_lpc_unrolled(
    int32_t *res, const int32_t *smp, int n,
    int order, const int32_t *coefs, int shift, int big)
{
    int i;
    for(i=order; i<n; i+=2) {
        int s = smp[i-order];
        int p0 = 0, p1 = 0;
        if(big) {
            switch(order) {
                case 32: LPC1(32)
                case 31: LPC1(31)
                case 30: LPC1(30)
                case 29: LPC1(29)
                case 28: LPC1(28)
                case 27: LPC1(27)
                case 26: LPC1(26)
                case 25: LPC1(25)
                case 24: LPC1(24)
                case 23: LPC1(23)
                case 22: LPC1(22)
                case 21: LPC1(21)
                case 20: LPC1(20)
                case 19: LPC1(19)
                case 18: LPC1(18)
                case 17: LPC1(17)
                case 16: LPC1(16)
                case 15: LPC1(15)
                case 14: LPC1(14)
                case 13: LPC1(13)
                case 12: LPC1(12)
                case 11: LPC1(11)
                case 10: LPC1(10)
                case  9: LPC1( 9)
                         LPC1( 8)
                         LPC1( 7)
                         LPC1( 6)
                         LPC1( 5)
                         LPC1( 4)
                         LPC1( 3)
                         LPC1( 2)
                         LPC1( 1)
            }
        } else {
            switch(order) {
                case  8: LPC1( 8)
                case  7: LPC1( 7)
                case  6: LPC1( 6)
                case  5: LPC1( 5)
                case  4: LPC1( 4)
                case  3: LPC1( 3)
                case  2: LPC1( 2)
                case  1: LPC1( 1)
            }
        }
        res[i  ] = smp[i  ] - (p0 >> shift);
        res[i+1] = smp[i+1] - (p1 >> shift);
    }
}

static void encode_residual_lpc(int32_t *res, const int32_t *smp, int n,
                                int order, const int32_t *coefs, int shift)
{
    int i;
    for(i=0; i<order; i++) {
        res[i] = smp[i];
    }
#ifdef CONFIG_SMALL
    for(i=order; i<n; i+=2) {
        int j;
        int s = smp[i];
        int p0 = 0, p1 = 0;
        for(j=0; j<order; j++) {
            int c = coefs[j];
            p1 += c*s;
            s = smp[i-j-1];
            p0 += c*s;
        }
        res[i  ] = smp[i  ] - (p0 >> shift);
        res[i+1] = smp[i+1] - (p1 >> shift);
    }
#else
    switch(order) {
        case  1: encode_residual_lpc_unrolled(res, smp, n, 1, coefs, shift, 0); break;
        case  2: encode_residual_lpc_unrolled(res, smp, n, 2, coefs, shift, 0); break;
        case  3: encode_residual_lpc_unrolled(res, smp, n, 3, coefs, shift, 0); break;
        case  4: encode_residual_lpc_unrolled(res, smp, n, 4, coefs, shift, 0); break;
        case  5: encode_residual_lpc_unrolled(res, smp, n, 5, coefs, shift, 0); break;
        case  6: encode_residual_lpc_unrolled(res, smp, n, 6, coefs, shift, 0); break;
        case  7: encode_residual_lpc_unrolled(res, smp, n, 7, coefs, shift, 0); break;
        case  8: encode_residual_lpc_unrolled(res, smp, n, 8, coefs, shift, 0); break;
        default: encode_residual_lpc_unrolled(res, smp, n, order, coefs, shift, 1); break;
    }
#endif
}

static int encode_residual(FlacEncodeContext *ctx, int ch)
{
    int i, n;
    int min_order, max_order, opt_order, precision, omethod;
    int min_porder, max_porder;
    FlacFrame *frame;
    FlacSubframe *sub;
    int32_t coefs[MAX_LPC_ORDER][MAX_LPC_ORDER];
    int shift[MAX_LPC_ORDER];
    int32_t *res, *smp;

    frame = &ctx->frame;
    sub = &frame->subframes[ch];
    res = sub->residual;
    smp = sub->samples;
    n = frame->blocksize;

    /* CONSTANT */
    for(i=1; i<n; i++) {
        if(smp[i] != smp[0]) break;
    }
    if(i == n) {
        sub->type = sub->type_code = FLAC_SUBFRAME_CONSTANT;
        res[0] = smp[0];
        return sub->obits;
    }

    /* VERBATIM */
    if(n < 5) {
        sub->type = sub->type_code = FLAC_SUBFRAME_VERBATIM;
        encode_residual_verbatim(res, smp, n);
        return sub->obits * n;
    }

    min_order = ctx->options.min_prediction_order;
    max_order = ctx->options.max_prediction_order;
    min_porder = ctx->options.min_partition_order;
    max_porder = ctx->options.max_partition_order;
    precision = ctx->options.lpc_coeff_precision;
    omethod = ctx->options.prediction_order_method;

    /* FIXED */
    if(!ctx->options.use_lpc || max_order == 0 || (n <= max_order)) {
        uint32_t bits[MAX_FIXED_ORDER+1];
        if(max_order > MAX_FIXED_ORDER) max_order = MAX_FIXED_ORDER;
        opt_order = 0;
        bits[0] = UINT32_MAX;
        for(i=min_order; i<=max_order; i++) {
            encode_residual_fixed(res, smp, n, i);
            bits[i] = calc_rice_params_fixed(&sub->rc, min_porder, max_porder, res,
                                             n, i, sub->obits);
            if(bits[i] < bits[opt_order]) {
                opt_order = i;
            }
        }
        sub->order = opt_order;
        sub->type = FLAC_SUBFRAME_FIXED;
        sub->type_code = sub->type | sub->order;
        if(sub->order != max_order) {
            encode_residual_fixed(res, smp, n, sub->order);
            return calc_rice_params_fixed(&sub->rc, min_porder, max_porder, res, n,
                                          sub->order, sub->obits);
        }
        return bits[sub->order];
    }

    /* LPC */
    opt_order = lpc_calc_coefs(ctx, smp, n, max_order, precision, coefs, shift, ctx->options.use_lpc, omethod);

    if(omethod == ORDER_METHOD_2LEVEL ||
       omethod == ORDER_METHOD_4LEVEL ||
       omethod == ORDER_METHOD_8LEVEL) {
        int levels = 1 << omethod;
        uint32_t bits[levels];
        int order;
        int opt_index = levels-1;
        opt_order = max_order-1;
        bits[opt_index] = UINT32_MAX;
        for(i=levels-1; i>=0; i--) {
            order = min_order + (((max_order-min_order+1) * (i+1)) / levels)-1;
            if(order < 0) order = 0;
            encode_residual_lpc(res, smp, n, order+1, coefs[order], shift[order]);
            bits[i] = calc_rice_params_lpc(&sub->rc, min_porder, max_porder,
                                           res, n, order+1, sub->obits, precision);
            if(bits[i] < bits[opt_index]) {
                opt_index = i;
                opt_order = order;
            }
        }
        opt_order++;
    } else if(omethod == ORDER_METHOD_SEARCH) {
        // brute-force optimal order search
        uint32_t bits[MAX_LPC_ORDER];
        opt_order = 0;
        bits[0] = UINT32_MAX;
        for(i=min_order-1; i<max_order; i++) {
            encode_residual_lpc(res, smp, n, i+1, coefs[i], shift[i]);
            bits[i] = calc_rice_params_lpc(&sub->rc, min_porder, max_porder,
                                           res, n, i+1, sub->obits, precision);
            if(bits[i] < bits[opt_order]) {
                opt_order = i;
            }
        }
        opt_order++;
    } else if(omethod == ORDER_METHOD_LOG) {
        uint32_t bits[MAX_LPC_ORDER];
        int step;

        opt_order= min_order - 1 + (max_order-min_order)/3;
        memset(bits, -1, sizeof(bits));

        for(step=16 ;step; step>>=1){
            int last= opt_order;
            for(i=last-step; i<=last+step; i+= step){
                if(i<min_order-1 || i>=max_order || bits[i] < UINT32_MAX)
                    continue;
                encode_residual_lpc(res, smp, n, i+1, coefs[i], shift[i]);
                bits[i] = calc_rice_params_lpc(&sub->rc, min_porder, max_porder,
                                            res, n, i+1, sub->obits, precision);
                if(bits[i] < bits[opt_order])
                    opt_order= i;
            }
        }
        opt_order++;
    }

    sub->order = opt_order;
    sub->type = FLAC_SUBFRAME_LPC;
    sub->type_code = sub->type | (sub->order-1);
    sub->shift = shift[sub->order-1];
    for(i=0; i<sub->order; i++) {
        sub->coefs[i] = coefs[sub->order-1][i];
    }
    encode_residual_lpc(res, smp, n, sub->order, sub->coefs, sub->shift);
    return calc_rice_params_lpc(&sub->rc, min_porder, max_porder, res, n, sub->order,