SQLite

u32 sqlite3BtreeLastPage(Btree *p){
  assert( sqlite3BtreeHoldsMutex(p) );
  assert( ((p->pBt->nPage)&0x8000000)==0 );
  return btreePagecount(p->pBt);
}

/*
** Get a page from the pager and initialize it.
**
** If pCur!=0 then the page acquired will be added to that cursor.
** If the fetch fails, this routine must decrement pCur->iPage.
**
** The page is fetched as read-write unless pCur is not NULL and is
** a read-only cursor.
**
** If an error occurs, then *ppPage is undefined. It
** may remain unchanged, or it may be set to an invalid value.
*/
static int getAndInitPage(
  BtShared *pBt,                  /* The database file */
  Pgno pgno,                      /* Number of the page to get */
  MemPage **ppPage,               /* Write the page pointer here */
  BtCursor *pCur,                 /* Cursor to receive the page, or NULL */
  int bReadOnly                   /* True for a read-only page */
){
  int rc;
  DbPage *pDbPage;
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pCur==0 || ppPage==&pCur->apPage[pCur->iPage] );
  assert( pCur==0 || bReadOnly==pCur->curPagerFlags );

  if( pgno>btreePagecount(pBt) ){
    rc = SQLITE_CORRUPT_BKPT;

    goto getAndInitPage_error;
  }
  rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, bReadOnly);
  if( rc ){
    goto getAndInitPage_error;
  }
  *ppPage = btreePageFromDbPage(pDbPage, pgno, pBt);
  if( (*ppPage)->isInit==0 ){
    rc = btreeInitPage(*ppPage);
    if( rc!=SQLITE_OK ){
      releasePage(*ppPage);
      goto getAndInitPage_error;
    }
  }

  /* If obtaining a page for a cursor, we must verify that the page is
  ** compatible with the cursor */
  if( pCur && pCur->iPage>0
   && ((*ppPage)->nCell<1 || (*ppPage)->intKey!=pCur->apPage[0]->intKey)
  ){
    rc = SQLITE_CORRUPT_BKPT;
    releasePage(*ppPage);
    goto getAndInitPage_error;
  }

  testcase( pgno==0 );
  assert( pgno!=0 || rc==SQLITE_CORRUPT );
  return SQLITE_OK;

getAndInitPage_error:
  if( pCur ) pCur->iPage--;
  return rc;
}

/*
** Release a MemPage.  This should be called once for each prior
** call to btreeGetPage.
*/

  pCur->pgnoRoot = (Pgno)iTable;
  pCur->iPage = -1;
  pCur->pKeyInfo = pKeyInfo;
  pCur->pBtree = p;
  pCur->pBt = pBt;
  assert( wrFlag==0 || wrFlag==BTCF_WriteFlag );
  pCur->curFlags = wrFlag;
  pCur->curPagerFlags = wrFlag ? 0 : PAGER_GET_READONLY;
  pCur->pNext = pBt->pCursor;
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur;
  }
  pBt->pCursor = pCur;
  pCur->eState = CURSOR_INVALID;
  return SQLITE_OK;

**
** This function returns SQLITE_CORRUPT if the page-header flags field of
** the new child page does not match the flags field of the parent (i.e.
** if an intkey page appears to be the parent of a non-intkey page, or
** vice-versa).
*/
static int moveToChild(BtCursor *pCur, u32 newPgno){



  BtShared *pBt = pCur->pBt;

  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage<BTCURSOR_MAX_DEPTH );
  assert( pCur->iPage>=0 );
  if( pCur->iPage>=(BTCURSOR_MAX_DEPTH-1) ){
    return SQLITE_CORRUPT_BKPT;
  }







  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  pCur->iPage++;


  pCur->aiIdx[pCur->iPage] = 0;
  return getAndInitPage(pBt, newPgno, &pCur->apPage[pCur->iPage],
                        pCur, pCur->curPagerFlags);
}

#if SQLITE_DEBUG
/*
** Page pParent is an internal (non-leaf) tree page. This function 
** asserts that page number iChild is the left-child if the iIdx'th
** cell in page pParent. Or, if iIdx is equal to the total number of

      assert( pCur->apPage[pCur->iPage]!=0 );
      releasePageNotNull(pCur->apPage[pCur->iPage--]);
    }
  }else if( pCur->pgnoRoot==0 ){
    pCur->eState = CURSOR_INVALID;
    return SQLITE_OK;
  }else{
    assert( pCur->iPage==(-1) );
    pCur->iPage = 0;
    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->apPage[0],
                        pCur, pCur->curPagerFlags);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    pCur->iPage = 0;
  }
  pRoot = pCur->apPage[0];

  if( (i+nxDiv-pParent->nOverflow)==pParent->nCell ){
    pRight = &pParent->aData[pParent->hdrOffset+8];
  }else{
    pRight = findCell(pParent, i+nxDiv-pParent->nOverflow);
  }
  pgno = get4byte(pRight);
  while( 1 ){
    rc = getAndInitPage(pBt, pgno, &apOld[i], 0, 0);
    if( rc ){
      memset(apOld, 0, (i+1)*sizeof(MemPage*));
      goto balance_cleanup;
    }
    nMaxCells += 1+apOld[i]->nCell+apOld[i]->nOverflow;
    if( (i--)==0 ) break;

  int hdr;
  u16 szCell;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno>btreePagecount(pBt) ){
    return SQLITE_CORRUPT_BKPT;
  }
  rc = getAndInitPage(pBt, pgno, &pPage, 0, 0);
  if( rc ) return rc;
  if( pPage->bBusy ){
    rc = SQLITE_CORRUPT_BKPT;
    goto cleardatabasepage_out;
  }
  pPage->bBusy = 1;
  hdr = pPage->hdrOffset;

  i64 nKey;                 /* Size of pKey, or last integer key */
  void *pKey;               /* Saved key that was cursor last known position */
  Pgno pgnoRoot;            /* The root page of this tree */
  int nOvflAlloc;           /* Allocated size of aOverflow[] array */
  int skipNext;    /* Prev() is noop if negative. Next() is noop if positive.
                   ** Error code if eState==CURSOR_FAULT */
  u8 curFlags;              /* zero or more BTCF_* flags defined below */
  u8 curPagerFlags;         /* Flags to send to sqlite3PagerAcquire() */
  u8 eState;                /* One of the CURSOR_XXX constants (see below) */
  u8 hints;                             /* As configured by CursorSetHints() */
  i16 iPage;                            /* Index of current page in apPage */
  u16 aiIdx[BTCURSOR_MAX_DEPTH];        /* Current index in apPage[i] */
  MemPage *apPage[BTCURSOR_MAX_DEPTH];  /* Pages from root to current page */
};