rockbox/apps/codecs/libmusepack/mpc_demux.c

/*
  Copyright (c) 2005-2009, The Musepack Development Team
  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:

  * Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

  * Redistributions in binary form must reproduce the above
  copyright notice, this list of conditions and the following
  disclaimer in the documentation and/or other materials provided
  with the distribution.

  * Neither the name of the The Musepack Development Team nor the
  names of its contributors may be used to endorse or promote
  products derived from this software without specific prior
  written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#include <math.h>
#include <string.h>
#include "streaminfo.h"
#include "mpcdec.h"
#include "internal.h"
#include "decoder.h"
#include "huffman.h"
#include "mpc_bits_reader.h"

#include <codeclib.h>

/// maximum number of seek points in the table. The distance between points will
/// be adapted so this value is never exceeded.
#define MAX_SEEK_TABLE_SIZE 8192

// globals
static mpc_uint8_t g_buffer[DEMUX_BUFFER_SIZE + MAX_FRAME_SIZE];
static mpc_seek_t g_seek_table[MAX_SEEK_TABLE_SIZE];
static mpc_demux g_mpc_demux IBSS_ATTR;

// streaminfo.c
mpc_status streaminfo_read_header_sv8(mpc_streaminfo* si,
                                      const mpc_bits_reader * r_in,
                                      mpc_size_t block_size);
mpc_status streaminfo_read_header_sv7(mpc_streaminfo* si, mpc_bits_reader * r_in);
void  streaminfo_encoder_info(mpc_streaminfo* si, const mpc_bits_reader * r_in);
void  streaminfo_gain(mpc_streaminfo* si, const mpc_bits_reader * r_in);

// mpc_decoder.c
void mpc_decoder_reset_scf(mpc_decoder * d, int value);

enum {
    MPC_BUFFER_SWAP = 1,
    MPC_BUFFER_FULL = 2,
};

static void mpc_demux_clear_buff(mpc_demux * d)
{
    d->bytes_total               = 0;
    d->bits_reader.buff          = d->buffer;
    d->bits_reader.count         = 8;
    d->bits_reader.buffered_addr = 0;
    d->bits_reader.buffered_code = 0;
    d->block_bits                = 0;
    d->block_frames              = 0;
    memset(d->buffer, 0, sizeof(g_buffer));
}

static mpc_uint32_t
mpc_demux_fill(mpc_demux * d, mpc_uint32_t min_bytes, int flags)
{
    mpc_uint32_t unread_bytes = d->bytes_total + d->buffer - d->bits_reader.buff
            - ((8 - d->bits_reader.count) >> 3);
    int offset = 0;

    if (min_bytes == 0 || min_bytes > DEMUX_BUFFER_SIZE ||
            (unread_bytes < min_bytes && flags & MPC_BUFFER_FULL))
        min_bytes = DEMUX_BUFFER_SIZE;

    if (unread_bytes < min_bytes) {
        mpc_uint32_t bytes2read = min_bytes - unread_bytes;
        mpc_uint32_t bytes_free = DEMUX_BUFFER_SIZE - d->bytes_total;

        if (flags & MPC_BUFFER_SWAP) {
            bytes2read &= -1 << 2;
            offset = (unread_bytes + 3) & ( -1 << 2);
            offset -= unread_bytes;
        }

        if (bytes2read > bytes_free) {
            if (d->bits_reader.count == 0) {
                d->bits_reader.count = 8;
                d->bits_reader.buff++;
            }
            memmove(d->buffer + offset, d->bits_reader.buff, unread_bytes);
            d->bits_reader.buff = d->buffer + offset;
            d->bytes_total = unread_bytes + offset;
        }
        bytes2read = d->r->read(d->r, d->buffer + d->bytes_total, bytes2read);
        if (flags & MPC_BUFFER_SWAP){
            unsigned int i, * tmp = (unsigned int *) (d->buffer + d->bytes_total);
            for(i = 0 ;i < (bytes2read >> 2); i++)
                tmp[i] = swap32(tmp[i]);
        }
        d->bytes_total += bytes2read;
        return bytes2read;
    }

    return (mpc_uint32_t) -1;
}

/**
 * seek to a bit position in the stream
 * @param d demuxer context
 * @param fpos position in the stream in bits from the beginning of mpc datas
 * @param min_bytes number of bytes to load after seeking
 */
static void
mpc_demux_seek(mpc_demux * d, mpc_seek_t fpos, mpc_uint32_t min_bytes) {
    mpc_seek_t next_pos;
    mpc_int_t bit_offset;

    // FIXME : do not flush the buffer if fpos is in the current buffer

    next_pos = fpos >> 3;
    if (d->si.stream_version == 7)
        next_pos = ((next_pos - d->si.header_position) & (-1 << 2)) + d->si.header_position;
    bit_offset = (int) (fpos - (next_pos << 3));

    d->r->seek(d->r, (mpc_int32_t) next_pos);
    mpc_demux_clear_buff(d);
    if (d->si.stream_version == 7)
        mpc_demux_fill(d, (min_bytes + ((bit_offset + 7) >> 3) + 3) & (~3), MPC_BUFFER_SWAP);
    else
        mpc_demux_fill(d, min_bytes + ((bit_offset + 7) >> 3), 0);
    d->bits_reader.buff += bit_offset >> 3;
    d->bits_reader.count = 8 - (bit_offset & 7);
}

/**
 * return the current position in the stream (in bits) from the beginning
 * of the file
 * @param d demuxer context
 * @return current stream position in bits
 */
mpc_seek_t mpc_demux_pos(mpc_demux * d)
{
    return (((mpc_seek_t)(d->r->tell(d->r)) - d->bytes_total +
             d->bits_reader.buff - d->buffer) << 3) + 8 - d->bits_reader.count;
}

/**
 * Searches for a ID3v2-tag and reads the length (in bytes) of it.
 *
 * @param d demuxer context
 * @return size of tag, in bytes
 * @return MPC_STATUS_FILE on errors of any kind
 */
static mpc_int32_t mpc_demux_skip_id3v2(mpc_demux * d)
{
    mpc_uint8_t  tmp [4];
    mpc_bool_t footerPresent;     // ID3v2.4-flag
    mpc_int32_t size;

    // we must be at the beginning of the stream
    mpc_demux_fill(d, 3, 0);

    // check id3-tag
    if ( 0 != memcmp( d->bits_reader.buff, "ID3", 3 ) )
        return 0;

    mpc_demux_fill(d, 10, 0);

    mpc_bits_read(&d->bits_reader, 24); // read ID3
    mpc_bits_read(&d->bits_reader, 16); // read tag version

    tmp[0] = mpc_bits_read(&d->bits_reader, 8); // read flags
    footerPresent = tmp[0] & 0x10;
    if ( tmp[0] & 0x0F )
        return MPC_STATUS_FILE; // not (yet???) allowed

    tmp[0] = mpc_bits_read(&d->bits_reader, 8); // read size
    tmp[1] = mpc_bits_read(&d->bits_reader, 8); // read size
    tmp[2] = mpc_bits_read(&d->bits_reader, 8); // read size
    tmp[3] = mpc_bits_read(&d->bits_reader, 8); // read size

    if ( (tmp[0] | tmp[1] | tmp[2] | tmp[3]) & 0x80 )
        return MPC_STATUS_FILE; // not allowed

    // read headerSize (syncsave: 4 * $0xxxxxxx = 28 significant bits)
    size = tmp[0] << 21;
    size |= tmp[1] << 14;
    size |= tmp[2] << 7;
    size |= tmp[3];

    size += 10; //header

    if ( footerPresent ) size += 10;

    // This is called before file headers get read, streamversion etc isn't yet known, demuxing isn't properly initialized and we can't call mpc_demux_seek() from here.
    mpc_demux_clear_buff(d);
    if (!d->r->seek(d->r, size)) return MPC_STATUS_FILE;

    return size;
}

static mpc_status mpc_demux_seek_init(mpc_demux * d)
{
    size_t seek_table_size;
    if (d->seek_table != 0)
        return MPC_STATUS_OK;

    d->seek_pwr = 6;
    if (d->si.block_pwr > d->seek_pwr)
        d->seek_pwr = d->si.block_pwr;
    seek_table_size = (2 + d->si.samples / (MPC_FRAME_LENGTH << d->seek_pwr));
    while (seek_table_size > MAX_SEEK_TABLE_SIZE) {
        d->seek_pwr++;
        seek_table_size = (2 + d->si.samples / (MPC_FRAME_LENGTH << d->seek_pwr));
    }
    d->seek_table = g_seek_table;
    if (d->seek_table == 0)
        return MPC_STATUS_FILE;
    d->seek_table[0] = (mpc_seek_t)mpc_demux_pos(d);
    d->seek_table_size = 1;

    return MPC_STATUS_OK;
}

static void mpc_demux_ST(mpc_demux * d)
{
    mpc_uint64_t tmp;
    mpc_seek_t * table, last[2];
    mpc_bits_reader r = d->bits_reader;
    mpc_uint_t i, diff_pwr = 0, mask;
    mpc_uint32_t file_table_size;

    if (d->seek_table != 0)
        return;

    mpc_bits_get_size(&r, &tmp);
    file_table_size = (mpc_seek_t) tmp;
    d->seek_pwr = d->si.block_pwr + mpc_bits_read(&r, 4);

    tmp = 2 + d->si.samples / (MPC_FRAME_LENGTH << d->seek_pwr);
    while (tmp > MAX_SEEK_TABLE_SIZE) {
        d->seek_pwr++;
        diff_pwr++;
        tmp = 2 + d->si.samples / (MPC_FRAME_LENGTH << d->seek_pwr);
    }
    if ((file_table_size >> diff_pwr) > tmp)
        file_table_size = tmp << diff_pwr;
    d->seek_table = g_seek_table;
    d->seek_table_size = (file_table_size + ((1 << diff_pwr) - 1)) >> diff_pwr;

    table = d->seek_table;
    mpc_bits_get_size(&r, &tmp);
    table[0] = last[0] = (mpc_seek_t) (tmp + d->si.header_position) * 8;

    if (d->seek_table_size == 1)
        return;

    mpc_bits_get_size(&r, &tmp);
    last[1] = (mpc_seek_t) (tmp + d->si.header_position) * 8;
    if (diff_pwr == 0) table[1] = last[1];

    mask = (1 << diff_pwr) - 1;
    for (i = 2; i < file_table_size; i++) {
        int code = mpc_bits_golomb_dec(&r, 12);
        if (code & 1)
            code = -(code & (-1 << 1));
        code <<= 2;
        last[i & 1] = code + 2 * last[(i-1) & 1] - last[i & 1];
        if ((i & mask) == 0)
            table[i >> diff_pwr] = last[i & 1];
    }
}

static void mpc_demux_SP(mpc_demux * d, int size, int block_size)
{
    mpc_seek_t cur;
    mpc_uint64_t ptr;
    mpc_block b;
    int st_head_size;

    cur = mpc_demux_pos(d);
    mpc_bits_get_size(&d->bits_reader, &ptr);
    mpc_demux_seek(d, (ptr - size) * 8 + cur, 11);
    st_head_size = mpc_bits_get_block(&d->bits_reader, &b);
    if (memcmp(b.key, "ST", 2) == 0) {
        d->chap_pos = (ptr - size + b.size + st_head_size) * 8 + cur;
        d->chap_nb = -1;
        mpc_demux_fill(d, (mpc_uint32_t) b.size, 0);
        mpc_demux_ST(d);
    }
    mpc_demux_seek(d, cur, 11 + block_size);
}
/* rockbox: not used
static void mpc_demux_chap_find(mpc_demux * d)
{
    mpc_block b;
    int tag_size = 0, chap_size = 0, size, i = 0;

    d->chap_nb = 0;

    if (d->si.stream_version < 8)
        return;

    if (d->chap_pos == 0) {
        mpc_uint64_t cur_pos = (d->si.header_position + 4) * 8;
        mpc_demux_seek(d, cur_pos, 11); // seek to the beginning of the stream
        size = mpc_bits_get_block(&d->bits_reader, &b);
        while (memcmp(b.key, "SE", 2) != 0) {
            if (mpc_check_key(b.key) != MPC_STATUS_OK)
                return;
            if (memcmp(b.key, "CT", 2) == 0) {
                if (d->chap_pos == 0) d->chap_pos = cur_pos;
            } else
                d->chap_pos = 0;
            cur_pos += (size + b.size) * 8;
            mpc_demux_seek(d, cur_pos, 11);
            size = mpc_bits_get_block(&d->bits_reader, &b);
        }
        if (d->chap_pos == 0)
            d->chap_pos = cur_pos;
    }

    mpc_demux_seek(d, d->chap_pos, 20);
    size = mpc_bits_get_block(&d->bits_reader, &b);
    while (memcmp(b.key, "CT", 2) == 0) {
        mpc_uint64_t chap_sample;
        d->chap_nb++;
        chap_size += size;
        size = mpc_bits_get_size(&d->bits_reader, &chap_sample) + 4;
        chap_size += size;
        tag_size += b.size - size;
        mpc_demux_seek(d, d->chap_pos + (chap_size + tag_size) * 8, 20);
        size = mpc_bits_get_block(&d->bits_reader, &b);
    }

    if (d->chap_nb > 0) {
        char * ptag;
        d->chap = malloc(sizeof(mpc_chap_info) * d->chap_nb + tag_size);
        ptag = (char*)(d->chap + d->chap_nb);

        mpc_demux_seek(d, d->chap_pos, 11);
        size = mpc_bits_get_block(&d->bits_reader, &b);
        while (memcmp(b.key, "CT", 2) == 0) {
            mpc_demux_fill(d, 11 + (mpc_uint32_t) b.size, 0);
            size = mpc_bits_get_size(&d->bits_reader, &d->chap[i].sample) + 4;
            d->chap[i].gain = (mpc_uint16_t) mpc_bits_read(&d->bits_reader, 16);
            d->chap[i].peak = (mpc_uint16_t) mpc_bits_read(&d->bits_reader, 16);
            memcpy(ptag, d->bits_reader.buff + ((8 - d->bits_reader.count) >> 3), b.size - size);
            d->bits_reader.buff += b.size - size;
            d->chap[i].tag_size = b.size - size;
            d->chap[i].tag = ptag;
            ptag += b.size - size;
            i++;
            size = mpc_bits_get_block(&d->bits_reader, &b);
        }
    }

    d->bits_reader.buff -= size;
}
*/

/**
 * Gets the number of chapters in the stream
 * @param d pointer to a musepack demuxer
 * @return the number of chapters found in the stream
 */
/* rockbox: not used
mpc_int_t mpc_demux_chap_nb(mpc_demux * d)
{
    if (d->chap_nb == -1)
        mpc_demux_chap_find(d);
    return d->chap_nb;
}
*/
/**
 * Gets datas associated to a given chapter
 * The chapter tag is an APEv2 tag without the preamble
 * @param d pointer to a musepack demuxer
 * @param chap_nb chapter number you want datas (from 0 to mpc_demux_chap_nb(d) - 1)
 * @return the chapter information structure
 */
/* rockbox: not used
mpc_chap_info const * mpc_demux_chap(mpc_demux * d, int chap_nb)
{
    if (d->chap_nb == -1)
        mpc_demux_chap_find(d);
    if (chap_nb >= d->chap_nb || chap_nb < 0)
        return 0;
    return &d->chap[chap_nb];
}
*/

static mpc_status mpc_demux_header(mpc_demux * d)
{
    char magic[4];

    d->si.pns = 0xFF;
/* rockbox: not used    
    d->si.profile_name = "n.a.";
*/
    // get header position
    d->si.header_position = mpc_demux_skip_id3v2(d);
    if(d->si.header_position < 0) return MPC_STATUS_FILE;

    d->si.tag_offset = d->si.total_file_length = d->r->get_size(d->r);

    mpc_demux_fill(d, 4, 0);
    magic[0] = mpc_bits_read(&d->bits_reader, 8);
    magic[1] = mpc_bits_read(&d->bits_reader, 8);
    magic[2] = mpc_bits_read(&d->bits_reader, 8);
    magic[3] = mpc_bits_read(&d->bits_reader, 8);

    if (memcmp(magic, "MP+", 3) == 0) {
        d->si.stream_version = magic[3] & 15;
        d->si.pns = magic[3] >> 4;
        if (d->si.stream_version == 7) {
            mpc_status ret;
            mpc_demux_fill(d, 6 * 4, MPC_BUFFER_SWAP); // header block size + endian convertion
            ret = streaminfo_read_header_sv7(&d->si, &d->bits_reader);
            if (ret != MPC_STATUS_OK) return ret;
        } else {
            return MPC_STATUS_INVALIDSV;
        }
    } else if (memcmp(magic, "MPCK", 4) == 0) {
        mpc_block b;
        int size;
        mpc_demux_fill(d, 11, 0); // max header block size
        size = mpc_bits_get_block(&d->bits_reader, &b);
        while( memcmp(b.key, "AP", 2) != 0 ){ // scan all blocks until audio
            if (mpc_check_key(b.key) != MPC_STATUS_OK)
                return MPC_STATUS_INVALIDSV;
            if (b.size > (mpc_uint64_t) DEMUX_BUFFER_SIZE - 11)
                return MPC_STATUS_INVALIDSV;
            mpc_demux_fill(d, 11 + (mpc_uint32_t) b.size, 0);
            if (memcmp(b.key, "SH", 2) == 0){
                int ret = streaminfo_read_header_sv8(&d->si, &d->bits_reader, (mpc_uint32_t) b.size);
                if (ret != MPC_STATUS_OK) return ret;
            } else if (memcmp(b.key, "RG", 2) == 0)
                streaminfo_gain(&d->si, &d->bits_reader);
            else if (memcmp(b.key, "EI", 2) == 0)
                streaminfo_encoder_info(&d->si, &d->bits_reader);
            else if (memcmp(b.key, "SO", 2) == 0)
                mpc_demux_SP(d, size, (mpc_uint32_t) b.size);
            else if (memcmp(b.key, "ST", 2) == 0)
                mpc_demux_ST(d);
            d->bits_reader.buff += b.size;
            size = mpc_bits_get_block(&d->bits_reader, &b);
        }
        d->bits_reader.buff -= size;
        if (d->si.stream_version == 0) // si not initialized !!!
            return MPC_STATUS_INVALIDSV;
    } else
        return MPC_STATUS_INVALIDSV;

    return MPC_STATUS_OK;
}

mpc_demux * mpc_demux_init(mpc_reader * p_reader)
{
    mpc_demux* p_tmp = &g_mpc_demux;

    if (p_tmp != 0) {
        memset(p_tmp, 0, sizeof(mpc_demux));
        p_tmp->buffer  = g_buffer;
        p_tmp->r       = p_reader;
        p_tmp->chap_nb = -1;
        mpc_demux_clear_buff(p_tmp);
        if (mpc_demux_header(p_tmp) == MPC_STATUS_OK &&
                  mpc_demux_seek_init(p_tmp) == MPC_STATUS_OK) {
            p_tmp->d = mpc_decoder_init(&p_tmp->si);
        } else {
            if (p_tmp->seek_table)
                memset(p_tmp->seek_table, 0, sizeof(g_seek_table));
            p_tmp = 0;
        }
    }

    return p_tmp;
}

void mpc_demux_exit(mpc_demux * d)
{
    mpc_decoder_exit(d->d);
    memset(d->seek_table, 0, sizeof(g_seek_table));
}

void mpc_demux_get_info(mpc_demux * d, mpc_streaminfo * i)
{
    memcpy(i, &d->si, sizeof d->si);
}

mpc_status mpc_demux_decode(mpc_demux * d, mpc_frame_info * i)
{
    mpc_bits_reader r;
    if (d->si.stream_version >= 8) {
        i->is_key_frame = MPC_FALSE;

        if (d->block_frames == 0) {
            mpc_block b = {{0,0},0};
            d->bits_reader.count &= -8;
            if (d->d->decoded_samples == (d->seek_table_size << d->seek_pwr) * MPC_FRAME_LENGTH) {
                d->seek_table[d->seek_table_size] = (mpc_seek_t) mpc_demux_pos(d);
                d->seek_table_size ++;
            }
            mpc_demux_fill(d, 11, 0); // max header block size
            mpc_bits_get_block(&d->bits_reader, &b);
            while( memcmp(b.key, "AP", 2) != 0 ) { // scan all blocks until audio
                if (mpc_check_key(b.key) != MPC_STATUS_OK)
                    goto error;
                if (memcmp(b.key, "SE", 2) == 0) { // end block
                    i->bits = -1;
                    return MPC_STATUS_OK;
                }
                if (mpc_demux_fill(d, 11 + (mpc_uint32_t) b.size, 0) == 0)
                    goto error;
                d->bits_reader.buff += b.size;
                mpc_bits_get_block(&d->bits_reader, &b);
            }
            d->block_bits = (mpc_uint32_t) b.size * 8;
            d->block_frames = 1 << d->si.block_pwr;
            i->is_key_frame = MPC_TRUE;
        }
        if (d->buffer + d->bytes_total - d->bits_reader.buff <= MAX_FRAME_SIZE)
            mpc_demux_fill(d, (d->block_bits >> 3) + 1, 0);
        r = d->bits_reader;
        mpc_decoder_decode_frame(d->d, &d->bits_reader, i);
        d->block_bits -= ((d->bits_reader.buff - r.buff) << 3) + r.count - d->bits_reader.count;
        d->block_frames--;
        if (d->block_bits < 0 || (d->block_frames == 0 && d->block_bits > 7))
            goto error;
    } else {
        if (d->d->decoded_samples == (d->seek_table_size << d->seek_pwr) * MPC_FRAME_LENGTH) {
            d->seek_table[d->seek_table_size] = (mpc_seek_t) mpc_demux_pos(d);
            d->seek_table_size ++;
        }
        mpc_demux_fill(d, MAX_FRAME_SIZE, MPC_BUFFER_FULL | MPC_BUFFER_SWAP);
        d->block_bits = (mpc_int_t) mpc_bits_read(&d->bits_reader, 20); // read frame size
        if (MPC_FRAME_LENGTH > d->d->samples - d->d->decoded_samples - 1) d->block_bits += 11; // we will read last frame size
        r = d->bits_reader;
        mpc_decoder_decode_frame(d->d, &d->bits_reader, i);
        if (i->bits != -1 && d->block_bits != (mpc_int32_t)(((d->bits_reader.buff - r.buff) << 3) + r.count - d->bits_reader.count))
            goto error;
    }
    if (i->bits != -1 && d->buffer + d->bytes_total < d->bits_reader.buff + ((8 - d->bits_reader.count) >> 3))
        goto error;

    return MPC_STATUS_OK;
error:
        i->bits = -1; // we pretend it's end of file
        return MPC_STATUS_INVALIDSV;
}

mpc_status mpc_demux_seek_second(mpc_demux * d, double seconds)
{
    return mpc_demux_seek_sample(d, (mpc_int64_t)(seconds * (double)d->si.sample_freq + 0.5));
}

mpc_status mpc_demux_seek_sample(mpc_demux * d, mpc_uint64_t destsample)
{
    mpc_uint32_t fwd, samples_to_skip, i;
    mpc_uint32_t block_samples = MPC_FRAME_LENGTH << d->si.block_pwr;
    mpc_seek_t fpos;

    destsample += d->si.beg_silence;
    if (destsample > d->si.samples) destsample = d->si.samples;
    fwd = (mpc_uint32_t) (destsample / block_samples);
    samples_to_skip = MPC_DECODER_SYNTH_DELAY +
            (mpc_uint32_t) (destsample % block_samples);
    if (d->si.stream_version == 7) {
        if (fwd > 32) {
            fwd -= 32;
            samples_to_skip += MPC_FRAME_LENGTH * 32;
        } else {
            samples_to_skip += MPC_FRAME_LENGTH * fwd;
            fwd = 0;
        }
    }

    i = fwd >> (d->seek_pwr - d->si.block_pwr);
    if (i >= d->seek_table_size)
        i = d->seek_table_size - 1;
    fpos = d->seek_table[i];
    i <<= d->seek_pwr - d->si.block_pwr;
    d->d->decoded_samples = i * block_samples;

    if (d->si.stream_version >= 8) {
        mpc_block b;
        int size;
        mpc_demux_seek(d, fpos, 11);
        size = mpc_bits_get_block(&d->bits_reader, &b);
        while(i < fwd) {
            if (memcmp(b.key, "AP", 2) == 0) {
                if (d->d->decoded_samples == (d->seek_table_size << d->seek_pwr) * MPC_FRAME_LENGTH) {
                    d->seek_table[d->seek_table_size] = (mpc_seek_t) mpc_demux_pos(d) - 8 * size;
                    d->seek_table_size ++;
                }
                d->d->decoded_samples += block_samples;
                i++;
            }
            fpos += ((mpc_uint32_t)b.size + size) * 8;
            mpc_demux_seek(d, fpos, 11);
            size = mpc_bits_get_block(&d->bits_reader, &b);
        }
        d->bits_reader.buff -= size;
    } else {
        mpc_decoder_reset_scf(d->d, fwd != 0);
        mpc_demux_seek(d, fpos, 4);
        for( ; i < fwd; i++){
            if (d->d->decoded_samples == (d->seek_table_size << d->seek_pwr) * MPC_FRAME_LENGTH) {
                d->seek_table[d->seek_table_size] = (mpc_seek_t) mpc_demux_pos(d);
                d->seek_table_size ++;
            }
            d->d->decoded_samples += block_samples;
            fpos += mpc_bits_read(&d->bits_reader, 20) + 20;
            mpc_demux_seek(d, fpos, 4);
        }
    }
    d->d->samples_to_skip = samples_to_skip;
    return MPC_STATUS_OK;
}

/* rockbox: not used
void mpc_set_replay_level(mpc_demux * d, float level, mpc_bool_t use_gain,
                          mpc_bool_t use_title, mpc_bool_t clip_prevention)
{
    float peak = use_title ? d->si.peak_title : d->si.peak_album;
    float gain = use_title ? d->si.gain_title : d->si.gain_album;

    if(!use_gain && !clip_prevention)
        return;

    if(!peak)
        peak = 1.;
    else
        peak = (1 << 15) / pow(10, peak / (20 * 256));

    if(!gain)
        gain = 1.;
    else
        gain = pow(10, (level - gain / 256) / 20);

    if(clip_prevention && (peak < gain || !use_gain))
        gain = peak;

    mpc_decoder_scale_output(d->d, gain);
}
*/