}
  return 0;
}

/*
** Return true if the page is already in the journal file.
*/
static int pageInJournal(PgHdr *pPg){
  return sqlite3BitvecTest(pPg->pPager->pInJournal, pPg->pgno);
}

/*
** Read a 32-bit integer from the given file descriptor.  Store the integer
** that is read in *pRes.  Return SQLITE_OK if everything worked, or an
** error code is something goes wrong.
**
................................................................................
  if( pPager->journalMode!=PAGER_JOURNALMODE_OFF ){

    /* Open the sub-journal, if it has not already been opened */
    assert( pPager->useJournal );
    assert( isOpen(pPager->jfd) || pagerUseWal(pPager) );
    assert( isOpen(pPager->sjfd) || pPager->nSubRec==0 );
    assert( pagerUseWal(pPager) 
         || pageInJournal(pPg) 
         || pPg->pgno>pPager->dbOrigSize 
    );
    rc = openSubJournal(pPager);

    /* If the sub-journal was opened successfully (or was already open),
    ** write the journal record into the file.  */
    if( rc==SQLITE_OK ){
................................................................................
** Mark a single data page as writeable. The page is written into the 
** main journal or sub-journal as required. If the page is written into
** one of the journals, the corresponding bit is set in the 
** Pager.pInJournal bitvec and the PagerSavepoint.pInSavepoint bitvecs
** of any open savepoints as appropriate.
*/
static int pager_write(PgHdr *pPg){
  void *pData = pPg->pData;
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;


  /* This routine is not called unless a write-transaction has already 
  ** been started. The journal file may or may not be open at this point.
  ** It is never called in the ERROR state.
  */
  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_CACHEMOD
................................................................................
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
  assert( assert_pager_state(pPager) );

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  sqlite3PcacheMakeDirty(pPg);

  if( pageInJournal(pPg) && (pPager->nSavepoint==0 || !subjRequiresPage(pPg)) ){
    assert( !pagerUseWal(pPager) );
  }else{
  
    /* The transaction journal now exists and we have a RESERVED or an
    ** EXCLUSIVE lock on the main database file.  Write the current page to
    ** the transaction journal if it is not there already.
    */
    if( !pageInJournal(pPg) && !pagerUseWal(pPager) ){
      assert( pagerUseWal(pPager)==0 );
      if( pPg->pgno<=pPager->dbOrigSize && isOpen(pPager->jfd) ){
        u32 cksum;
        char *pData2;
        i64 iOff = pPager->journalOff;

        /* We should never write to the journal file the page that
        ** contains the database locks.  The following assert verifies
        ** that we do not. */
        assert( pPg->pgno!=PAGER_MJ_PGNO(pPager) );

        assert( pPager->journalHdr<=pPager->journalOff );
        CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
        cksum = pager_cksum(pPager, (u8*)pData2);

        /* Even if an IO or diskfull error occurs while journalling the
        ** page in the block above, set the need-sync flag for the page.
        ** Otherwise, when the transaction is rolled back, the logic in
        ** playback_one_page() will think that the page needs to be restored
        ** in the database file. And if an IO error occurs while doing so,
................................................................................
    }
  
    /* If the statement journal is open and the page is not in it,
    ** then write the current page to the statement journal.  Note that
    ** the statement journal format differs from the standard journal format
    ** in that it omits the checksums and the header.
    */
    if( subjRequiresPage(pPg) ){
      rc = subjournalPage(pPg);
    }
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<pPg->pgno ){
................................................................................
  ** If the isCommit flag is set, there is no need to remember that
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( pPager->journalMode==PAGER_JOURNALMODE_OFF ||
            pageInJournal(pPg) || pPg->pgno>pPager->dbOrigSize );
    assert( pPg->flags&PGHDR_DIRTY );
  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PGHDR_NEED_SYNC flag was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.

  }
  return 0;
}

/*
** Return true if the page is already in the journal file.
*/
static int pageInJournal(Pager *pPager, PgHdr *pPg){
  return sqlite3BitvecTest(pPager->pInJournal, pPg->pgno);
}

/*
** Read a 32-bit integer from the given file descriptor.  Store the integer
** that is read in *pRes.  Return SQLITE_OK if everything worked, or an
** error code is something goes wrong.
**
................................................................................
  if( pPager->journalMode!=PAGER_JOURNALMODE_OFF ){

    /* Open the sub-journal, if it has not already been opened */
    assert( pPager->useJournal );
    assert( isOpen(pPager->jfd) || pagerUseWal(pPager) );
    assert( isOpen(pPager->sjfd) || pPager->nSubRec==0 );
    assert( pagerUseWal(pPager) 
         || pageInJournal(pPager, pPg) 
         || pPg->pgno>pPager->dbOrigSize 
    );
    rc = openSubJournal(pPager);

    /* If the sub-journal was opened successfully (or was already open),
    ** write the journal record into the file.  */
    if( rc==SQLITE_OK ){
................................................................................
** Mark a single data page as writeable. The page is written into the 
** main journal or sub-journal as required. If the page is written into
** one of the journals, the corresponding bit is set in the 
** Pager.pInJournal bitvec and the PagerSavepoint.pInSavepoint bitvecs
** of any open savepoints as appropriate.
*/
static int pager_write(PgHdr *pPg){

  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  int inJournal;

  /* This routine is not called unless a write-transaction has already 
  ** been started. The journal file may or may not be open at this point.
  ** It is never called in the ERROR state.
  */
  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_CACHEMOD
................................................................................
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
  assert( assert_pager_state(pPager) );

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  sqlite3PcacheMakeDirty(pPg);
  inJournal = pageInJournal(pPager, pPg);
  if( inJournal && (pPager->nSavepoint==0 || !subjRequiresPage(pPg)) ){
    assert( !pagerUseWal(pPager) );
  }else{
  
    /* The transaction journal now exists and we have a RESERVED or an
    ** EXCLUSIVE lock on the main database file.  Write the current page to
    ** the transaction journal if it is not there already.
    */
    if( !inJournal && !pagerUseWal(pPager) ){
      assert( pagerUseWal(pPager)==0 );
      if( pPg->pgno<=pPager->dbOrigSize && isOpen(pPager->jfd) ){
        u32 cksum;
        char *pData2;
        i64 iOff = pPager->journalOff;

        /* We should never write to the journal file the page that
        ** contains the database locks.  The following assert verifies
        ** that we do not. */
        assert( pPg->pgno!=PAGER_MJ_PGNO(pPager) );

        assert( pPager->journalHdr<=pPager->journalOff );
        CODEC2(pPager, pPg->pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
        cksum = pager_cksum(pPager, (u8*)pData2);

        /* Even if an IO or diskfull error occurs while journalling the
        ** page in the block above, set the need-sync flag for the page.
        ** Otherwise, when the transaction is rolled back, the logic in
        ** playback_one_page() will think that the page needs to be restored
        ** in the database file. And if an IO error occurs while doing so,
................................................................................
    }
  
    /* If the statement journal is open and the page is not in it,
    ** then write the current page to the statement journal.  Note that
    ** the statement journal format differs from the standard journal format
    ** in that it omits the checksums and the header.
    */
    if( pPager->nSavepoint>0 && subjRequiresPage(pPg) ){
      rc = subjournalPage(pPg);
    }
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<pPg->pgno ){
................................................................................
  ** If the isCommit flag is set, there is no need to remember that
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( pPager->journalMode==PAGER_JOURNALMODE_OFF ||
            pageInJournal(pPager, pPg) || pPg->pgno>pPager->dbOrigSize );
    assert( pPg->flags&PGHDR_DIRTY );
  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PGHDR_NEED_SYNC flag was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.