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/**
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 * @file encode.c
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 * @author Mathis Rosenhauer, Deutsches Klimarechenzentrum
 * @section DESCRIPTION
 *
 * Adaptive Entropy Encoder
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 * Based on CCSDS documents 121.0-B-2 and 120.0-G-2
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 *
 */
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#include <config.h>

#if HAVE_STDINT_H
# include <stdint.h>
#endif

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#include <stdio.h>
#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>

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#include "libaec.h"
#include "encode.h"
#include "encode_accessors.h"
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/* Marker for Remainder Of Segment condition in zero block encoding */
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#define ROS -1
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#define MIN(a, b) (((a) < (b))? (a): (b))

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static int m_get_block(struct aec_stream *strm);
static int m_get_block_cautious(struct aec_stream *strm);
static int m_check_zero_block(struct aec_stream *strm);
static int m_select_code_option(struct aec_stream *strm);
static int m_flush_block(struct aec_stream *strm);
static int m_flush_block_cautious(struct aec_stream *strm);
static int m_encode_splitting(struct aec_stream *strm);
static int m_encode_uncomp(struct aec_stream *strm);
static int m_encode_se(struct aec_stream *strm);
static int m_encode_zero(struct aec_stream *strm);

static inline void emit(struct internal_state *state,
                        uint32_t data, int bits)
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{
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    /**
       Emit sequence of bits.
     */

    if (bits <= state->bit_p) {
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        state->bit_p -= bits;
        *state->cds_p += data << state->bit_p;
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    } else {
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        bits -= state->bit_p;
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        *state->cds_p++ += (uint64_t)data >> bits;
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        while (bits & ~7) {
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            bits -= 8;
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            *state->cds_p++ = data >> bits;
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        }
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        state->bit_p = 8 - bits;
        *state->cds_p = data << state->bit_p;
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    }
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}

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static inline void emitfs(struct internal_state *state, int fs)
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{
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    /**
       Emits a fundamental sequence.
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       fs zero bits followed by one 1 bit.
     */
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    for(;;) {
        if (fs < state->bit_p) {
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            state->bit_p -= fs + 1;
            *state->cds_p += 1 << state->bit_p;
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            break;
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        } else {
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            fs -= state->bit_p;
            *++state->cds_p = 0;
            state->bit_p = 8;
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        }
    }
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}
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#define EMITBLOCK(ref)                                          \
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    static inline void emitblock_##ref(struct aec_stream *strm, \
                                       int k)                   \
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    {                                                           \
        int b;                                                  \
        uint64_t a;                                             \
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        struct internal_state *state = strm->state;             \
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        uint32_t *in = state->block_p + ref;                    \
        uint32_t *in_end = state->block_p + strm->block_size;   \
        uint64_t mask = (1ULL << k) - 1;                        \
        uint8_t *o = state->cds_p;                              \
        int p = state->bit_p;                                   \
                                                                \
        a = *o;                                                 \
                                                                \
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        while(in < in_end) {                                    \
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            a <<= 56;                                           \
            p = (p % 8) + 56;                                   \
                                                                \
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            while (p > k && in < in_end) {                      \
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                p -= k;                                         \
                a += ((uint64_t)(*in++) & mask) << p;           \
            }                                                   \
                                                                \
            for (b = 56; b > (p & ~7); b -= 8)                  \
                *o++ = a >> b;                                  \
            a >>= b;                                            \
        }                                                       \
                                                                \
        *o = a;                                                 \
        state->cds_p = o;                                       \
        state->bit_p = p % 8;                                   \
    }

EMITBLOCK(0);
EMITBLOCK(1);

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static void preprocess_unsigned(struct aec_stream *strm)
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{
    int i;
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    int64_t theta, Delta, prev;
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    struct internal_state *state = strm->state;
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    prev = state->block_buf[0];
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    for (i = 1; i < strm->rsi * strm->block_size; i++) {
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        theta = MIN(prev, state->xmax - prev);
        Delta = (int64_t)state->block_buf[i] - prev;
        prev = state->block_buf[i];
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        if (0 <= Delta && Delta <= theta) {
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            state->block_buf[i] = 2 * Delta;
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        } else if (-theta <= Delta && Delta < 0) {
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            state->block_buf[i] = 2
                * (Delta < 0 ? -(uint64_t)Delta : Delta) - 1;
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        } else {
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            state->block_buf[i] = theta
                + (Delta < 0 ? -(uint64_t)Delta : Delta);
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        }
    }
}

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static void preprocess_signed(struct aec_stream *strm)
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{
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    int i, m;
    int64_t theta, Delta, prev, sample;
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    struct internal_state *state = strm->state;
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    m = 64 - strm->bit_per_sample;
    prev = ((int64_t)state->block_buf[0] << m) >> m;
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    for (i = 1; i < strm->rsi * strm->block_size; i++) {
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        theta = MIN(prev - state->xmin, state->xmax - prev);
        sample = ((int64_t)state->block_buf[i] << m) >> m;
        Delta = sample - prev;
        prev = sample;

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        if (0 <= Delta && Delta <= theta) {
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            state->block_buf[i] = 2 * Delta;
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        } else if (-theta <= Delta && Delta < 0) {
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            state->block_buf[i] = 2
                * (Delta < 0 ? -(uint64_t)Delta : Delta) - 1;
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        } else {
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            state->block_buf[i] = theta
                + (Delta < 0 ? -(uint64_t)Delta : Delta);
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        }
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    }
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}
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/*
 *
 * FSM functions
 *
 */

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static int m_get_block(struct aec_stream *strm)
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{
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    struct internal_state *state = strm->state;
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    if (strm->avail_out > state->cds_len) {
        if (!state->direct_out) {
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            state->direct_out = 1;
            *strm->next_out = *state->cds_p;
            state->cds_p = strm->next_out;
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        }
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    } else {
        if (state->zero_blocks == 0 || state->direct_out) {
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            /* copy leftover from last block */
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            *state->cds_buf = *state->cds_p;
            state->cds_p = state->cds_buf;
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        }
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        state->direct_out = 0;
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    }
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    if (state->blocks_avail == 0) {
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        state->ref = 1;
        state->block_p = state->block_buf;
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        if (strm->avail_in >= state->block_len * strm->rsi) {
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            state->get_block(strm);
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            state->blocks_avail = strm->rsi - 1;
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            if (strm->flags & AEC_DATA_PREPROCESS)
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                state->preprocess(strm);
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            return m_check_zero_block(strm);
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        } else {
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            state->i = 0;
            state->mode = m_get_block_cautious;
        }
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    } else {
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        state->ref = 0;
        state->block_p += strm->block_size;
        state->blocks_avail--;
        return m_check_zero_block(strm);
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    }
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    return M_CONTINUE;
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}

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static int input_empty(struct aec_stream *strm)
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{
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    int j;
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    struct internal_state *state = strm->state;

    if (state->flush == AEC_FLUSH) {
        if (state->i > 0) {
            for (j = state->i; j < strm->rsi * strm->block_size; j++)
                state->block_buf[j] = state->block_buf[state->i - 1];
            state->i = strm->rsi * strm->block_size;
        } else {
            if (state->zero_blocks) {
                state->mode = m_encode_zero;
                return M_CONTINUE;
            }
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            emit(state, 0, state->bit_p);
            if (state->direct_out == 0)
                *strm->next_out++ = *state->cds_p;
            strm->avail_out--;
            strm->total_out++;
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            return M_EXIT;
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        }
    }
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    return M_EXIT;
}

static int m_get_block_cautious(struct aec_stream *strm)
{
    struct internal_state *state = strm->state;

    do {
        if (strm->avail_in > 0)
            state->block_buf[state->i] = state->get_sample(strm);
        else
            return input_empty(strm);
    } while (++state->i < strm->rsi * strm->block_size);
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    state->blocks_avail = strm->rsi - 1;
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    if (strm->flags & AEC_DATA_PREPROCESS)
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        state->preprocess(strm);
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    return m_check_zero_block(strm);
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}

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static int m_check_zero_block(struct aec_stream *strm)
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{
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    int i;
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    struct internal_state *state = strm->state;
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    i = state->ref;
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    while(i < strm->block_size && state->block_p[i] == 0)
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        i++;

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    if (i == strm->block_size) {
        if (state->zero_blocks == 0) {
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            state->zero_ref = state->ref;
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            state->zero_ref_sample = state->block_p[0];
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        }
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        state->zero_blocks++;
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        if ((strm->rsi - state->blocks_avail) % 64 == 0) {
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            if (state->zero_blocks > 4)
                state->zero_blocks = ROS;
            state->mode = m_encode_zero;
            return M_CONTINUE;
        }
        state->mode = m_get_block;
        return M_CONTINUE;
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    } else if (state->zero_blocks) {
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        /* The current block isn't zero but we have to emit a previous
         * zero block first. The current block will be handled
         * later.
         */
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        state->block_p -= strm->block_size;
        state->blocks_avail++;
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        state->mode = m_encode_zero;
        return M_CONTINUE;
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    }
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    state->mode = m_select_code_option;
    return M_CONTINUE;
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}

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static uint64_t block_fs(struct aec_stream *strm, int k)
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{
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    int j;
    uint64_t fs;
    struct internal_state *state = strm->state;

    fs = (uint64_t)(state->block_p[1] >> k)
        + (uint64_t)(state->block_p[2] >> k)
        + (uint64_t)(state->block_p[3] >> k)
        + (uint64_t)(state->block_p[4] >> k)
        + (uint64_t)(state->block_p[5] >> k)
        + (uint64_t)(state->block_p[6] >> k)
        + (uint64_t)(state->block_p[7] >> k);

    if (strm->block_size > 8)
        for (j = 1; j < strm->block_size / 8; j++)
            fs +=
                (uint64_t)(state->block_p[j * 8 + 0] >> k)
                + (uint64_t)(state->block_p[j * 8 + 1] >> k)
                + (uint64_t)(state->block_p[j * 8 + 2] >> k)
                + (uint64_t)(state->block_p[j * 8 + 3] >> k)
                + (uint64_t)(state->block_p[j * 8 + 4] >> k)
                + (uint64_t)(state->block_p[j * 8 + 5] >> k)
                + (uint64_t)(state->block_p[j * 8 + 6] >> k)
                + (uint64_t)(state->block_p[j * 8 + 7] >> k);

    if (state->ref == 0)
        fs += (uint64_t)(state->block_p[0] >> k);

    return fs;
}
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static int count_splitting_option(struct aec_stream *strm)
{
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    /**
       Find the best point for splitting samples in a block.

       In Rice coding each sample in a block of samples is split at
       the same position into k LSB and bit_per_sample - k MSB. The
       LSB part is left binary and the MSB part is coded as a
       fundamental sequence a.k.a. unary (see CCSDS 121.0-B-2). The
       function of the length of the Coded Data Set (CDS) depending on
       k has exactly one minimum (see A. Kiely, IPN Progress Report
       42-159).

       To find that minimum with only a few costly evaluations of the
       CDS length, we start with the k of the previous CDS. K is
       increased and the CDS length evaluated. If the CDS length gets
       smaller, then we are moving towards the minimum. If the length
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       increases, then the minimum will be found with smaller k.

       For increasing k we know that we will gain block_size bits in
       length through the larger binary part. If the FS lenth is less
       than the block size then a reduced FS part can't compensate the
       larger binary part. So we know that the CDS for k+1 will be
       larger than for k without actually computing the length. An
       analogue check can be done for decreasing k.

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     */

    int k, k_min;
    int this_bs; /* Block size of current block */
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    int no_turn; /* 1 if we shouldn't reverse */
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    int dir; /* Direction, 1 means increasing k, 0 decreasing k */
    uint64_t len; /* CDS length for current k */
    uint64_t len_min; /* CDS length minimum so far */
    uint64_t fs_len; /* Length of FS part (not including 1s) */

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    struct internal_state *state = strm->state;
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    this_bs = strm->block_size - state->ref;
    len_min = UINT64_MAX;
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    k = k_min = state->k;
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    no_turn = (k == 0) ? 1 : 0;
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    dir = 1;
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    for (;;) {
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        fs_len = block_fs(strm, k);
        len = fs_len + this_bs * (k + 1);
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        if (len < len_min) {
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            if (len_min < UINT64_MAX)
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                no_turn = 1;
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            len_min = len;
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            k_min = k;
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            if (dir) {
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                if (fs_len < this_bs || k >= state->kmax) {
                    if (no_turn)
                        break;
                    k = state->k - 1;
                    dir = 0;
                    no_turn = 1;
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                }
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                k++;
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            } else {
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                if (fs_len >= this_bs || k == 0)
                    break;
                k--;
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            }
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        } else {
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            if (no_turn)
                break;
            k = state->k - 1;
            dir = 0;
            no_turn = 1;
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        }
    }
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    state->k = k_min;
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    return len_min;
}

static int count_se_option(uint64_t limit, struct aec_stream *strm)
{
    int i;
    uint64_t d, len;
    struct internal_state *state = strm->state;

    len = 1;

    for (i = 0; i < strm->block_size; i+= 2) {
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        d = (uint64_t)state->block_p[i]
            + (uint64_t)state->block_p[i + 1];
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        /* we have to worry about overflow here */
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        if (d > limit) {
            len = UINT64_MAX;
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            break;
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        } else {
            len += d * (d + 1) / 2
                + (uint64_t)state->block_p[i + 1];
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        }
    }
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    return len;
}

static int m_select_code_option(struct aec_stream *strm)
{
    uint64_t uncomp_len, split_len, se_len;
    struct internal_state *state = strm->state;
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    uncomp_len = (strm->block_size - state->ref)
        * strm->bit_per_sample;
    split_len = count_splitting_option(strm);
    se_len = count_se_option(split_len, strm);
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    if (split_len < uncomp_len) {
        if (split_len < se_len)
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            return m_encode_splitting(strm);
        else
            return m_encode_se(strm);
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    } else {
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        if (uncomp_len <= se_len)
            return m_encode_uncomp(strm);
        else
            return m_encode_se(strm);
    }
}
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static int m_encode_splitting(struct aec_stream *strm)
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{
    int i;
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    struct internal_state *state = strm->state;
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    int k = state->k;
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    emit(state, k + 1, state->id_len);
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    if (state->ref)
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    {
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        emit(state, state->block_p[0], strm->bit_per_sample);
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        for (i = 1; i < strm->block_size; i++)
            emitfs(state, state->block_p[i] >> k);
        if (k) emitblock_1(strm, k);
    }
    else
    {
        for (i = 0; i < strm->block_size; i++)
            emitfs(state, state->block_p[i] >> k);
        if (k) emitblock_0(strm, k);
    }
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    return m_flush_block(strm);
}
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static int m_encode_uncomp(struct aec_stream *strm)
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{
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    struct internal_state *state = strm->state;
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    emit(state, (1 << state->id_len) - 1, state->id_len);
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    emitblock_0(strm, strm->bit_per_sample);
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    return m_flush_block(strm);
}
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static int m_encode_se(struct aec_stream *strm)
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{
    int i;
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    uint32_t d;
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    struct internal_state *state = strm->state;
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    emit(state, 1, state->id_len + 1);
    if (state->ref)
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        emit(state, state->block_p[0], strm->bit_per_sample);
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    for (i = 0; i < strm->block_size; i+= 2) {
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        d = state->block_p[i] + state->block_p[i + 1];
        emitfs(state, d * (d + 1) / 2 + state->block_p[i + 1]);
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    }
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    return m_flush_block(strm);
}
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static int m_encode_zero(struct aec_stream *strm)
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{
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    struct internal_state *state = strm->state;
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    emit(state, 0, state->id_len + 1);
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    if (state->zero_ref)
        emit(state, state->zero_ref_sample, strm->bit_per_sample);
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    if (state->zero_blocks == ROS)
        emitfs(state, 4);
    else if (state->zero_blocks >= 5)
        emitfs(state, state->zero_blocks);
    else
        emitfs(state, state->zero_blocks - 1);
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    state->zero_blocks = 0;
    return m_flush_block(strm);
}
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static int m_flush_block(struct aec_stream *strm)
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{
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    /**
       Flush block in direct_out mode by updating counters.

       Fall back to slow flushing if in buffered mode.
    */
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    int n;
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    struct internal_state *state = strm->state;
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    if (state->direct_out) {
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        n = state->cds_p - strm->next_out;
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        strm->next_out += n;
        strm->avail_out -= n;
        strm->total_out += n;
        state->mode = m_get_block;
        return M_CONTINUE;
    }
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    state->i = 0;
    state->mode = m_flush_block_cautious;
    return M_CONTINUE;
}

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static int m_flush_block_cautious(struct aec_stream *strm)
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{
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    /**
       Slow and restartable flushing
    */
    struct internal_state *state = strm->state;
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    while(state->cds_buf + state->i < state->cds_p) {
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        if (strm->avail_out == 0)
            return M_EXIT;

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        *strm->next_out++ = state->cds_buf[state->i];
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        strm->avail_out--;
        strm->total_out++;
        state->i++;
    }
    state->mode = m_get_block;
    return M_CONTINUE;
}

/*
 *
 * API functions
 *
 */
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int aec_encode_init(struct aec_stream *strm)
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{
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    int bs, bsi;
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    struct internal_state *state;
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    if (strm->bit_per_sample > 32 || strm->bit_per_sample == 0)
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        return AEC_CONF_ERROR;
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    if (strm->block_size != 8
        && strm->block_size != 16
        && strm->block_size != 32
        && strm->block_size != 64)
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        return AEC_CONF_ERROR;
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    if (strm->rsi > 4096)
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        return AEC_CONF_ERROR;
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    state = (struct internal_state *)malloc(sizeof(struct internal_state));
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    if (state == NULL)
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        return AEC_MEM_ERROR;
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    memset(state, 0, sizeof(struct internal_state));
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    strm->state = state;

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    bs = strm->block_size >> 3;
    bsi = 0;
    while (bs >>= 1)
        bsi++;

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    if (strm->bit_per_sample > 16) {
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        /* 24/32 input bit settings */
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        state->id_len = 5;

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        if (strm->bit_per_sample <= 24
            && strm->flags & AEC_DATA_3BYTE) {
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            state->block_len = 3 * strm->block_size;
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            if (strm->flags & AEC_DATA_MSB) {
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                state->get_sample = get_msb_24;
                state->get_block = get_block_funcs_msb_24[bsi];
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            } else {
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                state->get_sample = get_lsb_24;
                state->get_block = get_block_funcs_lsb_24[bsi];
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            }
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        } else {
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            state->block_len = 4 * strm->block_size;
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            if (strm->flags & AEC_DATA_MSB) {
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                state->get_sample = get_msb_32;
                state->get_block = get_block_funcs_msb_32[bsi];
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            } else {
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                state->get_sample = get_lsb_32;
                state->get_block = get_block_funcs_lsb_32[bsi];
            }
        }
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    }
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    else if (strm->bit_per_sample > 8) {
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        /* 16 bit settings */
        state->id_len = 4;
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        state->block_len = 2 * strm->block_size;
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        if (strm->flags & AEC_DATA_MSB) {
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            state->get_sample = get_msb_16;
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            state->get_block = get_block_funcs_msb_16[bsi];
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        } else {
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            state->get_sample = get_lsb_16;
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            state->get_block = get_block_funcs_lsb_16[bsi];
        }
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    } else {
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        /* 8 bit settings */
        state->id_len = 3;
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        state->block_len = strm->block_size;
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        state->get_sample = get_8;
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        state->get_block = get_block_funcs_8[bsi];
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    }

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    if (strm->flags & AEC_DATA_SIGNED) {
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        state->xmin = -(1ULL << (strm->bit_per_sample - 1));
        state->xmax = (1ULL << (strm->bit_per_sample - 1)) - 1;
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        state->preprocess = preprocess_signed;
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    } else {
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        state->xmin = 0;
        state->xmax = (1ULL << strm->bit_per_sample) - 1;
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        state->preprocess = preprocess_unsigned;
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    }

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    state->kmax = (1U << state->id_len) - 3;

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    state->block_buf = (uint32_t *)malloc(strm->rsi
                                         * strm->block_size
                                         * sizeof(uint32_t));
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    if (state->block_buf == NULL)
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        return AEC_MEM_ERROR;
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    state->block_p = state->block_buf;
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    /* Largest possible CDS according to specs */
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    state->cds_len = (5 + 64 * 32) / 8 + 3;
    state->cds_buf = (uint8_t *)malloc(state->cds_len);
    if (state->cds_buf == NULL)
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        return AEC_MEM_ERROR;
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    strm->total_in = 0;
    strm->total_out = 0;

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    state->cds_p = state->cds_buf;
    *state->cds_p = 0;
    state->bit_p = 8;
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    state->mode = m_get_block;

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    return AEC_OK;
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}

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int aec_encode(struct aec_stream *strm, int flush)
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{
    /**
       Finite-state machine implementation of the adaptive entropy
       encoder.
    */
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    int n;
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    struct internal_state *state;
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    state = strm->state;
    state->flush = flush;

    while (state->mode(strm) == M_CONTINUE);

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    if (state->direct_out) {
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        n = state->cds_p - strm->next_out;
        strm->next_out += n;
        strm->avail_out -= n;
        strm->total_out += n;

        *state->cds_buf = *state->cds_p;
        state->cds_p = state->cds_buf;
        state->direct_out = 0;
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    }
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    return AEC_OK;
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}

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int aec_encode_end(struct aec_stream *strm)
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{
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    struct internal_state *state = strm->state;
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    free(state->block_buf);
    free(state->cds_buf);
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    free(state);
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    return AEC_OK;
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}