ac3enc.c

/*
 * The simplest AC-3 encoder
 * Copyright (c) 2000 Fabrice Bellard
 * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
 * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
 *
 * 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
 */

/**
 * @file
 * The simplest AC-3 encoder.
 */

//#define ASSERT_LEVEL 2

#include <stdint.h>

#include "libavutil/audioconvert.h"
#include "libavutil/avassert.h"
#include "libavutil/avstring.h"
#include "libavutil/crc.h"
#include "libavutil/opt.h"
#include "avcodec.h"
#include "put_bits.h"
#include "dsputil.h"
#include "ac3dsp.h"
#include "ac3.h"
#include "audioconvert.h"
#include "fft.h"
#include "ac3enc.h"
#include "eac3enc.h"

typedef struct AC3Mant {
    int16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr; ///< mantissa pointers for bap=1,2,4
    int mant1_cnt, mant2_cnt, mant4_cnt;    ///< mantissa counts for bap=1,2,4
} AC3Mant;

#define CMIXLEV_NUM_OPTIONS 3
static const float cmixlev_options[CMIXLEV_NUM_OPTIONS] = {
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB
};

#define SURMIXLEV_NUM_OPTIONS 3
static const float surmixlev_options[SURMIXLEV_NUM_OPTIONS] = {
    LEVEL_MINUS_3DB, LEVEL_MINUS_6DB, LEVEL_ZERO
};

#define EXTMIXLEV_NUM_OPTIONS 8
static const float extmixlev_options[EXTMIXLEV_NUM_OPTIONS] = {
    LEVEL_PLUS_3DB,  LEVEL_PLUS_1POINT5DB,  LEVEL_ONE,       LEVEL_MINUS_4POINT5DB,
    LEVEL_MINUS_3DB, LEVEL_MINUS_4POINT5DB, LEVEL_MINUS_6DB, LEVEL_ZERO
};


/**
 * LUT for number of exponent groups.
 * exponent_group_tab[coupling][exponent strategy-1][number of coefficients]
 */
static uint8_t exponent_group_tab[2][3][256];


/**
 * List of supported channel layouts.
 */
const int64_t ff_ac3_channel_layouts[19] = {
     AV_CH_LAYOUT_MONO,
     AV_CH_LAYOUT_STEREO,
     AV_CH_LAYOUT_2_1,
     AV_CH_LAYOUT_SURROUND,
     AV_CH_LAYOUT_2_2,
     AV_CH_LAYOUT_QUAD,
     AV_CH_LAYOUT_4POINT0,
     AV_CH_LAYOUT_5POINT0,
     AV_CH_LAYOUT_5POINT0_BACK,
    (AV_CH_LAYOUT_MONO     | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_STEREO   | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_2_1      | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_2_2      | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_QUAD     | AV_CH_LOW_FREQUENCY),
    (AV_CH_LAYOUT_4POINT0  | AV_CH_LOW_FREQUENCY),
     AV_CH_LAYOUT_5POINT1,
     AV_CH_LAYOUT_5POINT1_BACK,
     0
};


/**
 * LUT to select the bandwidth code based on the bit rate, sample rate, and
 * number of full-bandwidth channels.
 * bandwidth_tab[fbw_channels-1][sample rate code][bit rate code]
 */
static const uint8_t ac3_bandwidth_tab[5][3][19] = {
//      32  40  48  56  64  80  96 112 128 160 192 224 256 320 384 448 512 576 640

    { {  0,  0,  0, 12, 16, 32, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0, 16, 20, 36, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0, 32, 40, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0, 20, 24, 32, 48, 48, 48, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  4, 24, 28, 36, 56, 56, 56, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0, 20, 44, 52, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 24, 32, 40, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  4, 20, 28, 36, 44, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0, 20, 40, 48, 60, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 12, 24, 32, 48, 48, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 16, 28, 36, 56, 56, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 32, 48, 60, 60, 60, 60, 60, 60, 60 } },

    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  8, 20, 32, 40, 48, 48, 48, 48 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 12, 24, 36, 44, 56, 56, 56, 56 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 28, 44, 60, 60, 60, 60, 60, 60 } }
};


/**
 * LUT to select the coupling start band based on the bit rate, sample rate, and
 * number of full-bandwidth channels. -1 = coupling off
 * ac3_coupling_start_tab[channel_mode-2][sample rate code][bit rate code]
 *
 * TODO: more testing for optimal parameters.
 *       multi-channel tests at 44.1kHz and 32kHz.
 */
static const int8_t ac3_coupling_start_tab[6][3][19] = {
//      32  40  48  56  64  80  96 112 128 160 192 224 256 320 384 448 512 576 640

    // 2/0
    { {  0,  0,  0,  0,  0,  0,  0,  1,  1,  7,  8, 11, 12, -1, -1, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  1,  3,  5,  7, 10, 12, 13, -1, -1, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  1,  2,  2,  9, 13, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 3/0
    { {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 2/1 - untested
    { {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  2,  2,  6,  9, 11, 12, 13, -1, -1, -1, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 3/1
    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 2/2 - untested
    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  3,  2, 10, 11, 11, 12, 12, 14, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },

    // 3/2
    { {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  6,  8, 11, 12, 12, -1, -1 },
      {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  6,  8, 11, 12, 12, -1, -1 },
      { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 } },
};


/**
 * Adjust the frame size to make the average bit rate match the target bit rate.
 * This is only needed for 11025, 22050, and 44100 sample rates or any E-AC-3.
 */
void ff_ac3_adjust_frame_size(AC3EncodeContext *s)
{
    while (s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
        s->bits_written    -= s->bit_rate;
        s->samples_written -= s->sample_rate;
    }
    s->frame_size = s->frame_size_min +
                    2 * (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
    s->bits_written    += s->frame_size * 8;
    s->samples_written += AC3_BLOCK_SIZE * s->num_blocks;
}


void ff_ac3_compute_coupling_strategy(AC3EncodeContext *s)
{
    int blk, ch;
    int got_cpl_snr;
    int num_cpl_blocks;

    /* set coupling use flags for each block/channel */
    /* TODO: turn coupling on/off and adjust start band based on bit usage */
    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = 1; ch <= s->fbw_channels; ch++)
            block->channel_in_cpl[ch] = s->cpl_on;
    }

    /* enable coupling for each block if at least 2 channels have coupling
       enabled for that block */
    got_cpl_snr = 0;
    num_cpl_blocks = 0;
    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        block->num_cpl_channels = 0;
        for (ch = 1; ch <= s->fbw_channels; ch++)
            block->num_cpl_channels += block->channel_in_cpl[ch];
        block->cpl_in_use = block->num_cpl_channels > 1;
        num_cpl_blocks += block->cpl_in_use;
        if (!block->cpl_in_use) {
            block->num_cpl_channels = 0;
            for (ch = 1; ch <= s->fbw_channels; ch++)
                block->channel_in_cpl[ch] = 0;
        }

        block->new_cpl_strategy = !blk;
        if (blk) {
            for (ch = 1; ch <= s->fbw_channels; ch++) {
                if (block->channel_in_cpl[ch] != s->blocks[blk-1].channel_in_cpl[ch]) {
                    block->new_cpl_strategy = 1;
                    break;
                }
            }
        }
        block->new_cpl_leak = block->new_cpl_strategy;

        if (!blk || (block->cpl_in_use && !got_cpl_snr)) {
            block->new_snr_offsets = 1;
            if (block->cpl_in_use)
                got_cpl_snr = 1;
        } else {
            block->new_snr_offsets = 0;
        }
    }
    if (!num_cpl_blocks)
        s->cpl_on = 0;

    /* set bandwidth for each channel */
    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = 1; ch <= s->fbw_channels; ch++) {
            if (block->channel_in_cpl[ch])
                block->end_freq[ch] = s->start_freq[CPL_CH];
            else
                block->end_freq[ch] = s->bandwidth_code * 3 + 73;
        }
    }
}


/**
 * Apply stereo rematrixing to coefficients based on rematrixing flags.
 */
void ff_ac3_apply_rematrixing(AC3EncodeContext *s)
{
    int nb_coefs;
    int blk, bnd, i;
    int start, end;
    uint8_t *flags;

    if (!s->rematrixing_enabled)
        return;

    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        if (block->new_rematrixing_strategy)
            flags = block->rematrixing_flags;
        nb_coefs = FFMIN(block->end_freq[1], block->end_freq[2]);
        for (bnd = 0; bnd < block->num_rematrixing_bands; bnd++) {
            if (flags[bnd]) {
                start = ff_ac3_rematrix_band_tab[bnd];
                end   = FFMIN(nb_coefs, ff_ac3_rematrix_band_tab[bnd+1]);
                for (i = start; i < end; i++) {
                    int32_t lt = block->fixed_coef[1][i];
                    int32_t rt = block->fixed_coef[2][i];
                    block->fixed_coef[1][i] = (lt + rt) >> 1;
                    block->fixed_coef[2][i] = (lt - rt) >> 1;
                }
            }
        }
    }
}


/**
 * Initialize exponent tables.
 */
static av_cold void exponent_init(AC3EncodeContext *s)
{
    int expstr, i, grpsize;

    for (expstr = EXP_D15-1; expstr <= EXP_D45-1; expstr++) {
        grpsize = 3 << expstr;
        for (i = 12; i < 256; i++) {
            exponent_group_tab[0][expstr][i] = (i + grpsize - 4) / grpsize;
            exponent_group_tab[1][expstr][i] = (i              ) / grpsize;
        }
    }
    /* LFE */
    exponent_group_tab[0][0][7] = 2;

    if (CONFIG_EAC3_ENCODER && s->eac3)
        ff_eac3_exponent_init();
}


/**
 * Extract exponents from the MDCT coefficients.
 */
static void extract_exponents(AC3EncodeContext *s)
{
    int ch        = !s->cpl_on;
    int chan_size = AC3_MAX_COEFS * s->num_blocks * (s->channels - ch + 1);
    AC3Block *block = &s->blocks[0];

    s->ac3dsp.extract_exponents(block->exp[ch], block->fixed_coef[ch], chan_size);
}


/**
 * Exponent Difference Threshold.
 * New exponents are sent if their SAD exceed this number.
 */
#define EXP_DIFF_THRESHOLD 500

/**
 * Table used to select exponent strategy based on exponent reuse block interval.
 */
static const uint8_t exp_strategy_reuse_tab[4][6] = {
    { EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
    { EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
    { EXP_D25, EXP_D25, EXP_D15, EXP_D15, EXP_D15, EXP_D15 },
    { EXP_D45, EXP_D25, EXP_D25, EXP_D15, EXP_D15, EXP_D15 }
};

/**
 * Calculate exponent strategies for all channels.
 * Array arrangement is reversed to simplify the per-channel calculation.
 */
static void compute_exp_strategy(AC3EncodeContext *s)
{
    int ch, blk, blk1;

    for (ch = !s->cpl_on; ch <= s->fbw_channels; ch++) {
        uint8_t *exp_strategy = s->exp_strategy[ch];
        uint8_t *exp          = s->blocks[0].exp[ch];
        int exp_diff;

        /* estimate if the exponent variation & decide if they should be
           reused in the next frame */
        exp_strategy[0] = EXP_NEW;
        exp += AC3_MAX_COEFS;
        for (blk = 1; blk < s->num_blocks; blk++, exp += AC3_MAX_COEFS) {
            if (ch == CPL_CH) {
                if (!s->blocks[blk-1].cpl_in_use) {
                    exp_strategy[blk] = EXP_NEW;
                    continue;
                } else if (!s->blocks[blk].cpl_in_use) {
                    exp_strategy[blk] = EXP_REUSE;
                    continue;
                }
            } else if (s->blocks[blk].channel_in_cpl[ch] != s->blocks[blk-1].channel_in_cpl[ch]) {
                exp_strategy[blk] = EXP_NEW;
                continue;
            }
            exp_diff = s->dsp.sad[0](NULL, exp, exp - AC3_MAX_COEFS, 16, 16);
            exp_strategy[blk] = EXP_REUSE;
            if (ch == CPL_CH && exp_diff > (EXP_DIFF_THRESHOLD * (s->blocks[blk].end_freq[ch] - s->start_freq[ch]) / AC3_MAX_COEFS))
                exp_strategy[blk] = EXP_NEW;
            else if (ch > CPL_CH && exp_diff > EXP_DIFF_THRESHOLD)
                exp_strategy[blk] = EXP_NEW;
        }

        /* now select the encoding strategy type : if exponents are often
           recoded, we use a coarse encoding */
        blk = 0;
        while (blk < s->num_blocks) {
            blk1 = blk + 1;
            while (blk1 < s->num_blocks && exp_strategy[blk1] == EXP_REUSE)
                blk1++;
            exp_strategy[blk] = exp_strategy_reuse_tab[s->num_blks_code][blk1-blk-1];
            blk = blk1;
        }
    }
    if (s->lfe_on) {
        ch = s->lfe_channel;
        s->exp_strategy[ch][0] = EXP_D15;
        for (blk = 1; blk < s->num_blocks; blk++)
            s->exp_strategy[ch][blk] = EXP_REUSE;
    }

    /* for E-AC-3, determine frame exponent strategy */
    if (CONFIG_EAC3_ENCODER && s->eac3)
        ff_eac3_get_frame_exp_strategy(s);
}


/**
 * Update the exponents so that they are the ones the decoder will decode.
 */
static void encode_exponents_blk_ch(uint8_t *exp, int nb_exps, int exp_strategy,
                                    int cpl)
{
    int nb_groups, i, k;

    nb_groups = exponent_group_tab[cpl][exp_strategy-1][nb_exps] * 3;

    /* for each group, compute the minimum exponent */
    switch(exp_strategy) {
    case EXP_D25:
        for (i = 1, k = 1-cpl; i <= nb_groups; i++) {
            uint8_t exp_min = exp[k];
            if (exp[k+1] < exp_min)
                exp_min = exp[k+1];
            exp[i-cpl] = exp_min;
            k += 2;
        }
        break;
    case EXP_D45:
        for (i = 1, k = 1-cpl; i <= nb_groups; i++) {
            uint8_t exp_min = exp[k];
            if (exp[k+1] < exp_min)
                exp_min = exp[k+1];
            if (exp[k+2] < exp_min)
                exp_min = exp[k+2];
            if (exp[k+3] < exp_min)
                exp_min = exp[k+3];
            exp[i-cpl] = exp_min;
            k += 4;
        }
        break;
    }

    /* constraint for DC exponent */
    if (!cpl && exp[0] > 15)
        exp[0] = 15;

    /* decrease the delta between each groups to within 2 so that they can be
       differentially encoded */
    for (i = 1; i <= nb_groups; i++)
        exp[i] = FFMIN(exp[i], exp[i-1] + 2);
    i--;
    while (--i >= 0)
        exp[i] = FFMIN(exp[i], exp[i+1] + 2);

    if (cpl)
        exp[-1] = exp[0] & ~1;

    /* now we have the exponent values the decoder will see */
    switch (exp_strategy) {
    case EXP_D25:
        for (i = nb_groups, k = (nb_groups * 2)-cpl; i > 0; i--) {
            uint8_t exp1 = exp[i-cpl];
            exp[k--] = exp1;
            exp[k--] = exp1;
        }
        break;
    case EXP_D45:
        for (i = nb_groups, k = (nb_groups * 4)-cpl; i > 0; i--) {
            exp[k] = exp[k-1] = exp[k-2] = exp[k-3] = exp[i-cpl];
            k -= 4;
        }
        break;
    }
}


/**
 * Encode exponents from original extracted form to what the decoder will see.
 * This copies and groups exponents based on exponent strategy and reduces
 * deltas between adjacent exponent groups so that they can be differentially
 * encoded.
 */
static void encode_exponents(AC3EncodeContext *s)
{
    int blk, blk1, ch, cpl;
    uint8_t *exp, *exp_strategy;
    int nb_coefs, num_reuse_blocks;

    for (ch = !s->cpl_on; ch <= s->channels; ch++) {
        exp          = s->blocks[0].exp[ch] + s->start_freq[ch];
        exp_strategy = s->exp_strategy[ch];

        cpl = (ch == CPL_CH);
        blk = 0;
        while (blk < s->num_blocks) {
            AC3Block *block = &s->blocks[blk];
            if (cpl && !block->cpl_in_use) {
                exp += AC3_MAX_COEFS;
                blk++;
                continue;
            }
            nb_coefs = block->end_freq[ch] - s->start_freq[ch];
            blk1 = blk + 1;

            /* count the number of EXP_REUSE blocks after the current block
               and set exponent reference block numbers */
            s->exp_ref_block[ch][blk] = blk;
            while (blk1 < s->num_blocks && exp_strategy[blk1] == EXP_REUSE) {
                s->exp_ref_block[ch][blk1] = blk;
                blk1++;
            }
            num_reuse_blocks = blk1 - blk - 1;

            /* for the EXP_REUSE case we select the min of the exponents */
            s->ac3dsp.ac3_exponent_min(exp-s->start_freq[ch], num_reuse_blocks,
                                       AC3_MAX_COEFS);

            encode_exponents_blk_ch(exp, nb_coefs, exp_strategy[blk], cpl);

            exp += AC3_MAX_COEFS * (num_reuse_blocks + 1);
            blk = blk1;
        }
    }

    /* reference block numbers have been changed, so reset ref_bap_set */
    s->ref_bap_set = 0;
}


/**
 * Count exponent bits based on bandwidth, coupling, and exponent strategies.
 */
static int count_exponent_bits(AC3EncodeContext *s)
{
    int blk, ch;
    int nb_groups, bit_count;

    bit_count = 0;
    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = !block->cpl_in_use; ch <= s->channels; ch++) {
            int exp_strategy = s->exp_strategy[ch][blk];
            int cpl          = (ch == CPL_CH);
            int nb_coefs     = block->end_freq[ch] - s->start_freq[ch];

            if (exp_strategy == EXP_REUSE)
                continue;

            nb_groups = exponent_group_tab[cpl][exp_strategy-1][nb_coefs];
            bit_count += 4 + (nb_groups * 7);
        }
    }

    return bit_count;
}


/**
 * Group exponents.
 * 3 delta-encoded exponents are in each 7-bit group. The number of groups
 * varies depending on exponent strategy and bandwidth.
 */
void ff_ac3_group_exponents(AC3EncodeContext *s)
{
    int blk, ch, i, cpl;
    int group_size, nb_groups;
    uint8_t *p;
    int delta0, delta1, delta2;
    int exp0, exp1;

    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = !block->cpl_in_use; ch <= s->channels; ch++) {
            int exp_strategy = s->exp_strategy[ch][blk];
            if (exp_strategy == EXP_REUSE)
                continue;
            cpl = (ch == CPL_CH);
            group_size = exp_strategy + (exp_strategy == EXP_D45);
            nb_groups = exponent_group_tab[cpl][exp_strategy-1][block->end_freq[ch]-s->start_freq[ch]];
            p = block->exp[ch] + s->start_freq[ch] - cpl;

            /* DC exponent */
            exp1 = *p++;
            block->grouped_exp[ch][0] = exp1;

            /* remaining exponents are delta encoded */
            for (i = 1; i <= nb_groups; i++) {
                /* merge three delta in one code */
                exp0   = exp1;
                exp1   = p[0];
                p     += group_size;
                delta0 = exp1 - exp0 + 2;
                av_assert2(delta0 >= 0 && delta0 <= 4);

                exp0   = exp1;
                exp1   = p[0];
                p     += group_size;
                delta1 = exp1 - exp0 + 2;
                av_assert2(delta1 >= 0 && delta1 <= 4);

                exp0   = exp1;
                exp1   = p[0];
                p     += group_size;
                delta2 = exp1 - exp0 + 2;
                av_assert2(delta2 >= 0 && delta2 <= 4);

                block->grouped_exp[ch][i] = ((delta0 * 5 + delta1) * 5) + delta2;
            }
        }
    }
}


/**
 * Calculate final exponents from the supplied MDCT coefficients and exponent shift.
 * Extract exponents from MDCT coefficients, calculate exponent strategies,
 * and encode final exponents.
 */
void ff_ac3_process_exponents(AC3EncodeContext *s)
{
    extract_exponents(s);

    compute_exp_strategy(s);

    encode_exponents(s);

    emms_c();
}


/**
 * Count frame bits that are based solely on fixed parameters.
 * This only has to be run once when the encoder is initialized.
 */
static void count_frame_bits_fixed(AC3EncodeContext *s)
{
    static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };
    int blk;
    int frame_bits;

    /* assumptions:
     *   no dynamic range codes
     *   bit allocation parameters do not change between blocks
     *   no delta bit allocation
     *   no skipped data
     *   no auxilliary data
     *   no E-AC-3 metadata
     */

    /* header */
    frame_bits = 16; /* sync info */
    if (s->eac3) {
        /* bitstream info header */
        frame_bits += 35;
        frame_bits += 1 + 1;
        if (s->num_blocks != 0x6)
            frame_bits++;
        frame_bits++;
        /* audio frame header */
        if (s->num_blocks == 6)
            frame_bits += 2;
        frame_bits += 10;
        /* exponent strategy */
        if (s->use_frame_exp_strategy)
            frame_bits += 5 * s->fbw_channels;
        else
            frame_bits += s->num_blocks * 2 * s->fbw_channels;
        if (s->lfe_on)
            frame_bits += s->num_blocks;
        /* converter exponent strategy */
        if (s->num_blks_code != 0x3)
            frame_bits++;
        else
            frame_bits += s->fbw_channels * 5;
        /* snr offsets */
        frame_bits += 10;
        /* block start info */
        if (s->num_blocks != 1)
            frame_bits++;
    } else {
        frame_bits += 49;
        frame_bits += frame_bits_inc[s->channel_mode];
    }

    /* audio blocks */
    for (blk = 0; blk < s->num_blocks; blk++) {
        if (!s->eac3) {
            /* block switch flags */
            frame_bits += s->fbw_channels;

            /* dither flags */
            frame_bits += s->fbw_channels;
        }

        /* dynamic range */
        frame_bits++;

        /* spectral extension */
        if (s->eac3)
            frame_bits++;

        if (!s->eac3) {
            /* exponent strategy */
            frame_bits += 2 * s->fbw_channels;
            if (s->lfe_on)
                frame_bits++;

            /* bit allocation params */
            frame_bits++;
            if (!blk)
                frame_bits += 2 + 2 + 2 + 2 + 3;
        }

        /* converter snr offset */
        if (s->eac3)
            frame_bits++;

        if (!s->eac3) {
            /* delta bit allocation */
            frame_bits++;

            /* skipped data */
            frame_bits++;
        }
    }

    /* auxiliary data */
    frame_bits++;

    /* CRC */
    frame_bits += 1 + 16;

    s->frame_bits_fixed = frame_bits;
}


/**
 * Initialize bit allocation.
 * Set default parameter codes and calculate parameter values.
 */
static void bit_alloc_init(AC3EncodeContext *s)
{
    int ch;

    /* init default parameters */
    s->slow_decay_code = 2;
    s->fast_decay_code = 1;
    s->slow_gain_code  = 1;
    s->db_per_bit_code = s->eac3 ? 2 : 3;
    s->floor_code      = 7;
    for (ch = 0; ch <= s->channels; ch++)
        s->fast_gain_code[ch] = 4;

    /* initial snr offset */
    s->coarse_snr_offset = 40;

    /* compute real values */
    /* currently none of these values change during encoding, so we can just
       set them once at initialization */
    s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->bit_alloc.sr_shift;
    s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->bit_alloc.sr_shift;
    s->bit_alloc.slow_gain  = ff_ac3_slow_gain_tab[s->slow_gain_code];
    s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];
    s->bit_alloc.floor      = ff_ac3_floor_tab[s->floor_code];
    s->bit_alloc.cpl_fast_leak = 0;
    s->bit_alloc.cpl_slow_leak = 0;

    count_frame_bits_fixed(s);
}


/**
 * Count the bits used to encode the frame, minus exponents and mantissas.
 * Bits based on fixed parameters have already been counted, so now we just
 * have to add the bits based on parameters that change during encoding.
 */
static void count_frame_bits(AC3EncodeContext *s)
{
    AC3EncOptions *opt = &s->options;
    int blk, ch;
    int frame_bits = 0;

    /* header */
    if (s->eac3) {
        if (opt->eac3_mixing_metadata) {
            if (s->channel_mode > AC3_CHMODE_STEREO)
                frame_bits += 2;
            if (s->has_center)
                frame_bits += 6;
            if (s->has_surround)
                frame_bits += 6;
            frame_bits += s->lfe_on;
            frame_bits += 1 + 1 + 2;
            if (s->channel_mode < AC3_CHMODE_STEREO)
                frame_bits++;
            frame_bits++;
        }
        if (opt->eac3_info_metadata) {
            frame_bits += 3 + 1 + 1;
            if (s->channel_mode == AC3_CHMODE_STEREO)
                frame_bits += 2 + 2;
            if (s->channel_mode >= AC3_CHMODE_2F2R)
                frame_bits += 2;
            frame_bits++;
            if (opt->audio_production_info)
                frame_bits += 5 + 2 + 1;
            frame_bits++;
        }
        /* coupling */
        if (s->channel_mode > AC3_CHMODE_MONO) {
            frame_bits++;
            for (blk = 1; blk < s->num_blocks; blk++) {
                AC3Block *block = &s->blocks[blk];
                frame_bits++;
                if (block->new_cpl_strategy)
                    frame_bits++;
            }
        }
        /* coupling exponent strategy */
        if (s->cpl_on) {
            if (s->use_frame_exp_strategy) {
                frame_bits += 5 * s->cpl_on;
            } else {
                for (blk = 0; blk < s->num_blocks; blk++)
                    frame_bits += 2 * s->blocks[blk].cpl_in_use;
            }
        }
    } else {
        if (opt->audio_production_info)
            frame_bits += 7;
        if (s->bitstream_id == 6) {
            if (opt->extended_bsi_1)
                frame_bits += 14;
            if (opt->extended_bsi_2)
                frame_bits += 14;
        }
    }

    /* audio blocks */
    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];

        /* coupling strategy */
        if (!s->eac3)
            frame_bits++;
        if (block->new_cpl_strategy) {
            if (!s->eac3)
                frame_bits++;
            if (block->cpl_in_use) {
                if (s->eac3)
                    frame_bits++;
                if (!s->eac3 || s->channel_mode != AC3_CHMODE_STEREO)
                    frame_bits += s->fbw_channels;
                if (s->channel_mode == AC3_CHMODE_STEREO)
                    frame_bits++;
                frame_bits += 4 + 4;
                if (s->eac3)
                    frame_bits++;
                else
                    frame_bits += s->num_cpl_subbands - 1;
            }
        }

        /* coupling coordinates */
        if (block->cpl_in_use) {
            for (ch = 1; ch <= s->fbw_channels; ch++) {
                if (block->channel_in_cpl[ch]) {
                    if (!s->eac3 || block->new_cpl_coords[ch] != 2)
                        frame_bits++;
                    if (block->new_cpl_coords[ch]) {
                        frame_bits += 2;
                        frame_bits += (4 + 4) * s->num_cpl_bands;
                    }
                }
            }
        }

        /* stereo rematrixing */
        if (s->channel_mode == AC3_CHMODE_STEREO) {
            if (!s->eac3 || blk > 0)
                frame_bits++;
            if (s->blocks[blk].new_rematrixing_strategy)
                frame_bits += block->num_rematrixing_bands;
        }

        /* bandwidth codes & gain range */
        for (ch = 1; ch <= s->fbw_channels; ch++) {
            if (s->exp_strategy[ch][blk] != EXP_REUSE) {
                if (!block->channel_in_cpl[ch])
                    frame_bits += 6;
                frame_bits += 2;
            }
        }

        /* coupling exponent strategy */
        if (!s->eac3 && block->cpl_in_use)
            frame_bits += 2;

        /* snr offsets and fast gain codes */
        if (!s->eac3) {
            frame_bits++;
            if (block->new_snr_offsets)
                frame_bits += 6 + (s->channels + block->cpl_in_use) * (4 + 3);
        }

        /* coupling leak info */
        if (block->cpl_in_use) {
            if (!s->eac3 || block->new_cpl_leak != 2)
                frame_bits++;
            if (block->new_cpl_leak)
                frame_bits += 3 + 3;
        }
    }

    s->frame_bits = s->frame_bits_fixed + frame_bits;
}


/**
 * Calculate masking curve based on the final exponents.
 * Also calculate the power spectral densities to use in future calculations.
 */
static void bit_alloc_masking(AC3EncodeContext *s)
{
    int blk, ch;

    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        for (ch = !block->cpl_in_use; ch <= s->channels; ch++) {
            /* We only need psd and mask for calculating bap.
               Since we currently do not calculate bap when exponent
               strategy is EXP_REUSE we do not need to calculate psd or mask. */
            if (s->exp_strategy[ch][blk] != EXP_REUSE) {
                ff_ac3_bit_alloc_calc_psd(block->exp[ch], s->start_freq[ch],
                                          block->end_freq[ch], block->psd[ch],
                                          block->band_psd[ch]);
                ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, block->band_psd[ch],
                                           s->start_freq[ch], block->end_freq[ch],
                                           ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],
                                           ch == s->lfe_channel,
                                           DBA_NONE, 0, NULL, NULL, NULL,
                                           block->mask[ch]);
            }
        }
    }
}


/**
 * Ensure that bap for each block and channel point to the current bap_buffer.
 * They may have been switched during the bit allocation search.
 */
static void reset_block_bap(AC3EncodeContext *s)
{
    int blk, ch;
    uint8_t *ref_bap;

    if (s->ref_bap[0][0] == s->bap_buffer && s->ref_bap_set)
        return;

    ref_bap = s->bap_buffer;
    for (ch = 0; ch <= s->channels; ch++) {
        for (blk = 0; blk < s->num_blocks; blk++)
            s->ref_bap[ch][blk] = ref_bap + AC3_MAX_COEFS * s->exp_ref_block[ch][blk];
        ref_bap += AC3_MAX_COEFS * s->num_blocks;
    }
    s->ref_bap_set = 1;
}


/**
 * Initialize mantissa counts.
 * These are set so that they are padded to the next whole group size when bits
 * are counted in compute_mantissa_size.
 */
static void count_mantissa_bits_init(uint16_t mant_cnt[AC3_MAX_BLOCKS][16])
{
    int blk;

    for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
        memset(mant_cnt[blk], 0, sizeof(mant_cnt[blk]));
        mant_cnt[blk][1] = mant_cnt[blk][2] = 2;
        mant_cnt[blk][4] = 1;
    }
}


/**
 * Update mantissa bit counts for all blocks in 1 channel in a given bandwidth
 * range.
 */
static void count_mantissa_bits_update_ch(AC3EncodeContext *s, int ch,
                                          uint16_t mant_cnt[AC3_MAX_BLOCKS][16],
                                          int start, int end)
{
    int blk;

    for (blk = 0; blk < s->num_blocks; blk++) {
        AC3Block *block = &s->blocks[blk];
        if (ch == CPL_CH && !block->cpl_in_use)
            continue;