SQLite

** Using this cache reduces the number of calls to btreeParseCell().
*/
#ifndef NDEBUG
  static void assertCellInfo(BtCursor *pCur){
    CellInfo info;
    int iPage = pCur->iPage;
    memset(&info, 0, sizeof(info));
    btreeParseCell(pCur->apPage[iPage], pCur->aiIdx[iPage], &info);
    assert( CORRUPT_DB || memcmp(&info, &pCur->info, sizeof(info))==0 );
  }
#else
  #define assertCellInfo(x)
#endif
static SQLITE_NOINLINE void getCellInfo(BtCursor *pCur){
  if( pCur->info.nSize==0 ){
    int iPage = pCur->iPage;
    pCur->curFlags |= BTCF_ValidNKey;
    btreeParseCell(pCur->apPage[iPage],pCur->aiIdx[iPage],&pCur->info);
  }else{
    assertCellInfo(pCur);
  }
}

#ifndef NDEBUG  /* The next routine used only within assert() statements */
/*

#ifdef SQLITE_DIRECT_OVERFLOW_READ
  unsigned char * const pBufStart = pBuf;     /* Start of original out buffer */
#endif

  assert( pPage );
  assert( eOp==0 || eOp==1 );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->aiIdx[pCur->iPage]<pPage->nCell );
  assert( cursorHoldsMutex(pCur) );

  getCellInfo(pCur);
  aPayload = pCur->info.pPayload;
  assert( offset+amt <= pCur->info.nPayload );

  assert( aPayload > pPage->aData );

** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.
*/
int sqlite3BtreePayload(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage>=0 && pCur->apPage[pCur->iPage] );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  return accessPayload(pCur, offset, amt, (unsigned char*)pBuf, 0);
}

/*
** This variant of sqlite3BtreePayload() works even if the cursor has not
** in the CURSOR_VALID state.  It is only used by the sqlite3_blob_read()
** interface.

  u32 *pAmt            /* Write the number of available bytes here */
){
  u32 amt;
  assert( pCur!=0 && pCur->iPage>=0 && pCur->apPage[pCur->iPage]);
  assert( pCur->eState==CURSOR_VALID );
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
  assert( cursorOwnsBtShared(pCur) );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  assert( pCur->info.nSize>0 );
  assert( pCur->info.pPayload>pCur->apPage[pCur->iPage]->aData || CORRUPT_DB );
  assert( pCur->info.pPayload<pCur->apPage[pCur->iPage]->aDataEnd ||CORRUPT_DB);
  amt = (int)(pCur->apPage[pCur->iPage]->aDataEnd - pCur->info.pPayload);
  if( pCur->info.nLocal<amt ) amt = pCur->info.nLocal;
  *pAmt = amt;
  return (void*)pCur->info.pPayload;

  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);
}

#ifdef SQLITE_DEBUG
/*
** Page pParent is an internal (non-leaf) tree page. This function 

    pCur->apPage[pCur->iPage-1], 
    pCur->aiIdx[pCur->iPage-1], 
    pCur->apPage[pCur->iPage]->pgno
  );
  testcase( pCur->aiIdx[pCur->iPage-1] > pCur->apPage[pCur->iPage-1]->nCell );
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);

  releasePageNotNull(pCur->apPage[pCur->iPage--]);
}

/*
** Move the cursor to point to the root page of its b-tree structure.
**
** If the table has a virtual root page, then the cursor is moved to point

  ** (or the freelist).  */
  assert( pRoot->intKey==1 || pRoot->intKey==0 );
  if( pRoot->isInit==0 || (pCur->pKeyInfo==0)!=pRoot->intKey ){
    return SQLITE_CORRUPT_BKPT;
  }

skip_init:  
  pCur->aiIdx[0] = 0;
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidNKey|BTCF_ValidOvfl);

  pRoot = pCur->apPage[0];
  if( pRoot->nCell>0 ){
    pCur->eState = CURSOR_VALID;
  }else if( !pRoot->leaf ){

  Pgno pgno;
  int rc = SQLITE_OK;
  MemPage *pPage;

  assert( cursorOwnsBtShared(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  while( rc==SQLITE_OK && !(pPage = pCur->apPage[pCur->iPage])->leaf ){
    assert( pCur->aiIdx[pCur->iPage]<pPage->nCell );
    pgno = get4byte(findCell(pPage, pCur->aiIdx[pCur->iPage]));
    rc = moveToChild(pCur, pgno);
  }
  return rc;
}

/*
** Move the cursor down to the right-most leaf entry beneath the

  int rc = SQLITE_OK;
  MemPage *pPage = 0;

  assert( cursorOwnsBtShared(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  while( !(pPage = pCur->apPage[pCur->iPage])->leaf ){
    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    pCur->aiIdx[pCur->iPage] = pPage->nCell;
    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
  }
  pCur->aiIdx[pCur->iPage] = pPage->nCell-1;
  assert( pCur->info.nSize==0 );
  assert( (pCur->curFlags & BTCF_ValidNKey)==0 );
  return SQLITE_OK;
}

/* Move the cursor to the first entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something

#ifdef SQLITE_DEBUG
    /* This block serves to assert() that the cursor really does point 
    ** to the last entry in the b-tree. */
    int ii;
    for(ii=0; ii<pCur->iPage; ii++){
      assert( pCur->aiIdx[ii]==pCur->apPage[ii]->nCell );
    }
    assert( pCur->aiIdx[pCur->iPage]==pCur->apPage[pCur->iPage]->nCell-1 );
    assert( pCur->apPage[pCur->iPage]->leaf );
#endif
    return SQLITE_OK;
  }

  rc = moveToRoot(pCur);
  if( rc==SQLITE_OK ){

    ** a moveToChild() or moveToRoot() call would have detected corruption.  */
    assert( pPage->nCell>0 );
    assert( pPage->intKey==(pIdxKey==0) );
    lwr = 0;
    upr = pPage->nCell-1;
    assert( biasRight==0 || biasRight==1 );
    idx = upr>>(1-biasRight); /* idx = biasRight ? upr : (lwr+upr)/2; */
    pCur->aiIdx[pCur->iPage] = (u16)idx;
    if( xRecordCompare==0 ){
      for(;;){
        i64 nCellKey;
        pCell = findCellPastPtr(pPage, idx);
        if( pPage->intKeyLeaf ){
          while( 0x80 <= *(pCell++) ){
            if( pCell>=pPage->aDataEnd ) return SQLITE_CORRUPT_BKPT;
          }
        }
        getVarint(pCell, (u64*)&nCellKey);
        if( nCellKey<intKey ){
          lwr = idx+1;
          if( lwr>upr ){ c = -1; break; }
        }else if( nCellKey>intKey ){
          upr = idx-1;
          if( lwr>upr ){ c = +1; break; }
        }else{
          assert( nCellKey==intKey );
          pCur->aiIdx[pCur->iPage] = (u16)idx;
          if( !pPage->leaf ){
            lwr = idx;
            goto moveto_next_layer;
          }else{
            pCur->curFlags |= BTCF_ValidNKey;
            pCur->info.nKey = nCellKey;
            pCur->info.nSize = 0;

            goto moveto_finish;
          }
          pCellKey = sqlite3Malloc( nCell+18 );
          if( pCellKey==0 ){
            rc = SQLITE_NOMEM_BKPT;
            goto moveto_finish;
          }
          pCur->aiIdx[pCur->iPage] = (u16)idx;
          rc = accessPayload(pCur, 0, nCell, (unsigned char*)pCellKey, 0);
          pCur->curFlags &= ~BTCF_ValidOvfl;
          if( rc ){
            sqlite3_free(pCellKey);
            goto moveto_finish;
          }
          c = xRecordCompare(nCell, pCellKey, pIdxKey);

          lwr = idx+1;
        }else if( c>0 ){
          upr = idx-1;
        }else{
          assert( c==0 );
          *pRes = 0;
          rc = SQLITE_OK;
          pCur->aiIdx[pCur->iPage] = (u16)idx;
          if( pIdxKey->errCode ) rc = SQLITE_CORRUPT;
          goto moveto_finish;
        }
        if( lwr>upr ) break;
        assert( lwr+upr>=0 );
        idx = (lwr+upr)>>1;  /* idx = (lwr+upr)/2 */
      }
    }
    assert( lwr==upr+1 || (pPage->intKey && !pPage->leaf) );
    assert( pPage->isInit );
    if( pPage->leaf ){
      assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
      pCur->aiIdx[pCur->iPage] = (u16)idx;
      *pRes = c;
      rc = SQLITE_OK;
      goto moveto_finish;
    }
moveto_next_layer:
    if( lwr>=pPage->nCell ){
      chldPg = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    }else{
      chldPg = get4byte(findCell(pPage, lwr));
    }
    pCur->aiIdx[pCur->iPage] = (u16)lwr;
    rc = moveToChild(pCur, chldPg);
    if( rc ) break;
  }
moveto_finish:
  pCur->info.nSize = 0;
  assert( (pCur->curFlags & BTCF_ValidOvfl)==0 );
  return rc;

        return SQLITE_OK;
      }
      pCur->skipNext = 0;
    }
  }

  pPage = pCur->apPage[pCur->iPage];
  idx = ++pCur->aiIdx[pCur->iPage];
  assert( pPage->isInit );

  /* If the database file is corrupt, it is possible for the value of idx 
  ** to be invalid here. This can only occur if a second cursor modifies
  ** the page while cursor pCur is holding a reference to it. Which can
  ** only happen if the database is corrupt in such a way as to link the
  ** page into more than one b-tree structure. */

      if( pCur->iPage==0 ){
        *pRes = 1;
        pCur->eState = CURSOR_INVALID;
        return SQLITE_OK;
      }
      moveToParent(pCur);
      pPage = pCur->apPage[pCur->iPage];
    }while( pCur->aiIdx[pCur->iPage]>=pPage->nCell );
    if( pPage->intKey ){
      return sqlite3BtreeNext(pCur, pRes);
    }else{
      return SQLITE_OK;
    }
  }
  if( pPage->leaf ){

  assert( *pRes==0 || *pRes==1 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  *pRes = 0;
  if( pCur->eState!=CURSOR_VALID ) return btreeNext(pCur, pRes);
  pPage = pCur->apPage[pCur->iPage];
  if( (++pCur->aiIdx[pCur->iPage])>=pPage->nCell ){
    pCur->aiIdx[pCur->iPage]--;
    return btreeNext(pCur, pRes);
  }
  if( pPage->leaf ){
    return SQLITE_OK;
  }else{
    return moveToLeftmost(pCur);
  }

      pCur->skipNext = 0;
    }
  }

  pPage = pCur->apPage[pCur->iPage];
  assert( pPage->isInit );
  if( !pPage->leaf ){
    int idx = pCur->aiIdx[pCur->iPage];
    rc = moveToChild(pCur, get4byte(findCell(pPage, idx)));
    if( rc ) return rc;
    rc = moveToRightmost(pCur);
  }else{
    while( pCur->aiIdx[pCur->iPage]==0 ){
      if( pCur->iPage==0 ){
        pCur->eState = CURSOR_INVALID;
        *pRes = 1;
        return SQLITE_OK;
      }
      moveToParent(pCur);
    }
    assert( pCur->info.nSize==0 );
    assert( (pCur->curFlags & (BTCF_ValidOvfl))==0 );

    pCur->aiIdx[pCur->iPage]--;
    pPage = pCur->apPage[pCur->iPage];
    if( pPage->intKey && !pPage->leaf ){
      rc = sqlite3BtreePrevious(pCur, pRes);
    }else{
      rc = SQLITE_OK;
    }
  }
  return rc;
}
int sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
  assert( cursorOwnsBtShared(pCur) );
  assert( pRes!=0 );
  assert( *pRes==0 || *pRes==1 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  *pRes = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidOvfl|BTCF_ValidNKey);
  pCur->info.nSize = 0;
  if( pCur->eState!=CURSOR_VALID
   || pCur->aiIdx[pCur->iPage]==0
   || pCur->apPage[pCur->iPage]->leaf==0
  ){
    return btreePrevious(pCur, pRes);
  }
  pCur->aiIdx[pCur->iPage]--;
  return SQLITE_OK;
}

/*
** Allocate a new page from the database file.
**
** The new page is marked as dirty.  (In other words, sqlite3PagerWrite()

        ** next iteration of the do-loop will balance the child page.
        */ 
        assert( balance_deeper_called==0 );
        VVA_ONLY( balance_deeper_called++ );
        rc = balance_deeper(pPage, &pCur->apPage[1]);
        if( rc==SQLITE_OK ){
          pCur->iPage = 1;
          pCur->aiIdx[0] = 0;
          pCur->aiIdx[1] = 0;
          assert( pCur->apPage[1]->nOverflow );
        }
      }else{
        break;
      }
    }else if( pPage->nOverflow==0 && pPage->nFree<=nMin ){
      break;

  assert( pPage->isInit );
  newCell = pBt->pTmpSpace;
  assert( newCell!=0 );
  rc = fillInCell(pPage, newCell, pX, &szNew);
  if( rc ) goto end_insert;
  assert( szNew==pPage->xCellSize(pPage, newCell) );
  assert( szNew <= MX_CELL_SIZE(pBt) );
  idx = pCur->aiIdx[pCur->iPage];
  if( loc==0 ){
    CellInfo info;
    assert( idx<pPage->nCell );
    rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc ){
      goto end_insert;
    }

      memcpy(oldCell, newCell, szNew);
      return SQLITE_OK;
    }
    dropCell(pPage, idx, info.nSize, &rc);
    if( rc ) goto end_insert;
  }else if( loc<0 && pPage->nCell>0 ){
    assert( pPage->leaf );
    idx = ++pCur->aiIdx[pCur->iPage];
  }else{
    assert( pPage->leaf );
  }
  insertCell(pPage, idx, newCell, szNew, 0, 0, &rc);
  assert( pPage->nOverflow==0 || rc==SQLITE_OK );
  assert( rc!=SQLITE_OK || pPage->nCell>0 || pPage->nOverflow>0 );

  assert( cursorOwnsBtShared(pCur) );
  assert( pBt->inTransaction==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( pCur->curFlags & BTCF_WriteFlag );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );
  assert( !hasReadConflicts(p, pCur->pgnoRoot) );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  assert( pCur->eState==CURSOR_VALID );
  assert( (flags & ~(BTREE_SAVEPOSITION | BTREE_AUXDELETE))==0 );

  iCellDepth = pCur->iPage;
  iCellIdx = pCur->aiIdx[iCellDepth];
  pPage = pCur->apPage[iCellDepth];
  pCell = findCell(pPage, iCellIdx);

  /* If the bPreserve flag is set to true, then the cursor position must
  ** be preserved following this delete operation. If the current delete
  ** will cause a b-tree rebalance, then this is done by saving the cursor
  ** key and leaving the cursor in CURSOR_REQUIRESEEK state before 

    if( bSkipnext ){
      assert( bPreserve && (pCur->iPage==iCellDepth || CORRUPT_DB) );
      assert( pPage==pCur->apPage[pCur->iPage] || CORRUPT_DB );
      assert( (pPage->nCell>0 || CORRUPT_DB) && iCellIdx<=pPage->nCell );
      pCur->eState = CURSOR_SKIPNEXT;
      if( iCellIdx>=pPage->nCell ){
        pCur->skipNext = -1;
        pCur->aiIdx[iCellDepth] = pPage->nCell-1;
      }else{
        pCur->skipNext = 1;
      }
    }else{
      rc = moveToRoot(pCur);
      if( bPreserve ){
        pCur->eState = CURSOR_REQUIRESEEK;

      do {
        if( pCur->iPage==0 ){
          /* All pages of the b-tree have been visited. Return successfully. */
          *pnEntry = nEntry;
          return moveToRoot(pCur);
        }
        moveToParent(pCur);
      }while ( pCur->aiIdx[pCur->iPage]>=pCur->apPage[pCur->iPage]->nCell );

      pCur->aiIdx[pCur->iPage]++;
      pPage = pCur->apPage[pCur->iPage];
    }

    /* Descend to the child node of the cell that the cursor currently 
    ** points at. This is the right-child if (iIdx==pPage->nCell).
    */
    iIdx = pCur->aiIdx[pCur->iPage];
    if( iIdx==pPage->nCell ){
      rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+8]));
    }else{
      rc = moveToChild(pCur, get4byte(findCell(pPage, iIdx)));
    }
  }

  u8 eState;                /* One of the CURSOR_XXX constants (see below) */
  u8 hints;                 /* As configured by CursorSetHints() */
  /* All fields above are zeroed when the cursor is allocated.  See
  ** sqlite3BtreeCursorZero().  Fields that follow must be manually
  ** initialized. */
  i8 iPage;                 /* Index of current page in apPage */
  u8 curIntKey;             /* Value of apPage[0]->intKey */

  struct KeyInfo *pKeyInfo; /* Argument passed to comparison function */
  void *padding1;           /* Make object size a multiple of 16 */
  u16 aiIdx[BTCURSOR_MAX_DEPTH];        /* Current index in apPage[i] */
  MemPage *apPage[BTCURSOR_MAX_DEPTH];  /* Pages from root to current page */
};

/*