SQLite

#if !defined(NDEBUG) && !defined(SQLITE_DEBUG)
# define NDEBUG 1
#endif
#if defined(NDEBUG) && defined(SQLITE_DEBUG)
# undef NDEBUG
#endif

/* SQLITE_DEBUG_COLUMNCACHE is synomous with SQLITE_DEBUG.  The 
** SQLITE_DEBUG_COLUMNCACHE symbol only exists to provide a convenient
** way to search for all code that deals with verifying correct behavior
** of the column cache.
*/
#ifdef SQLITE_DEBUG
# define SQLITE_DEBUG_COLUMNCACHE 1
#else
# undef SQLIT_DEBUG_COLUMNCACHE
#endif

/*
** Enable SQLITE_ENABLE_EXPLAIN_COMMENTS if SQLITE_DEBUG is turned on.
*/
#if !defined(SQLITE_ENABLE_EXPLAIN_COMMENTS) && defined(SQLITE_DEBUG)
# define SQLITE_ENABLE_EXPLAIN_COMMENTS 1
#endif

*/
#ifdef SQLITE_DEBUG
# define memAboutToChange(P,M) sqlite3VdbeMemAboutToChange(P,M)
#else
# define memAboutToChange(P,M)
#endif

/*
** Given a cursor number and a column for a table or index, compute a
** hash value for use in the Mem.iTabColHash value.  The iTabColHash
** column is only used for verification - it is omitted from production
** builds.  Collisions are harmless in the sense that the correct answer
** still results.  The only harm of collisions is that they can potential
** reduce column-cache error detection during SQLITE_DEBUG builds.
**
** No valid hash should be 0.
*/
#define TableColumnHash(T,C)  (((u32)(T)<<16)^(u32)(C+2))

/*
** The following global variable is incremented every time a cursor
** moves, either by the OP_SeekXX, OP_Next, or OP_Prev opcodes.  The test
** procedures use this information to make sure that indices are
** working correctly.  This variable has no function other than to
** help verify the correct operation of the library.
*/

  assert( pOut!=pIn1 );
  while( 1 ){
    memAboutToChange(p, pOut);
    sqlite3VdbeMemShallowCopy(pOut, pIn1, MEM_Ephem);
    Deephemeralize(pOut);
#ifdef SQLITE_DEBUG
    pOut->pScopyFrom = 0;
    pOut->iTabColHash = 0;
#endif
    REGISTER_TRACE(pOp->p2+pOp->p3-n, pOut);
    if( (n--)==0 ) break;
    pOut++;
    pIn1++;
  }
  break;

** An Abort is safe if either there have been no writes, or if there is
** an active statement journal.
*/
case OP_Abortable: {
  sqlite3VdbeAssertAbortable(p);
  break;
}
#endif

#ifdef SQLITE_DEBUG_COLUMNCACHE
/* Opcode:  SetTabCol   P1 P2 P3 * *
**
** Set a flag in register REG[P3] indicating that it holds the value
** of column P2 from the table on cursor P1.  This flag is checked
** by a subsequent VerifyTabCol opcode.
**
** This opcode only appears SQLITE_DEBUG builds.  It is used to verify
** that the expression table column cache is working correctly.
*/
case OP_SetTabCol: {
  aMem[pOp->p3].iTabColHash = TableColumnHash(pOp->p1,pOp->p2);
  break;
}
/* Opcode:  VerifyTabCol   P1 P2 P3 * *
**
** Verify that register REG[P3] contains the value of column P2 from
** cursor P1.  Assert() if this is not the case.
**
** This opcode only appears SQLITE_DEBUG builds.  It is used to verify
** that the expression table column cache is working correctly.
*/
case OP_VerifyTabCol: {
  assert( aMem[pOp->p3].iTabColHash == TableColumnHash(pOp->p1,pOp->p2) );
  break;
}
#endif

/* Opcode: Noop * * * * *
**
** Do nothing.  This instruction is often useful as a jump
** destination.
*/

  u32 uTemp;          /* Transient storage for serial_type in OP_MakeRecord */
  sqlite3 *db;        /* The associated database connection */
  void (*xDel)(void*);/* Destructor for Mem.z - only valid if MEM_Dyn */
#ifdef SQLITE_DEBUG
  Mem *pScopyFrom;    /* This Mem is a shallow copy of pScopyFrom */
  u16 mScopyFlags;    /* flags value immediately after the shallow copy */
#endif
#ifdef SQLITE_DEBUG_COLUMNCACHE
  u32 iTabColHash;    /* Hash of table.column that is origin of this value */
  u32 iPadding;       /* sqlite3_value objects must be 8-byte aligned */
#endif
};

/*
** Size of struct Mem not including the Mem.zMalloc member or anything that
** follows.
*/
#define MEMCELLSIZE offsetof(Mem,zMalloc)

        /* .uTemp      = */ (u32)0,
        /* .db         = */ (sqlite3*)0,
        /* .xDel       = */ (void(*)(void*))0,
#ifdef SQLITE_DEBUG
        /* .pScopyFrom = */ (Mem*)0,
        /* .mScopyFlags= */ 0,
#endif
#ifdef SQLITE_DEBUG_COLUMNCACHE
        /* .iTabColHash= */ 0,
#endif
      };
  return &nullMem;
}

/*
** Check to see if column iCol of the given statement is valid.  If
** it is, return a pointer to the Mem for the value of that column.

  while( (N--)>0 ){
    p->db = db;
    p->flags = flags;
    p->szMalloc = 0;
#ifdef SQLITE_DEBUG
    p->pScopyFrom = 0;
#endif
#ifdef SQLITE_DEBUG_COLUMNCACHE
    p->iTabColHash = 0;
#endif
    p++;
  }
}

/*
** Release an array of N Mem elements
*/

      /* pMem is the register that is changing.  But also mark pX as
      ** undefined so that we can quickly detect the shallow-copy error */
      pX->flags = MEM_Undefined;
      pX->pScopyFrom = 0;
    }
  }
  pMem->pScopyFrom = 0;
#ifdef SQLITE_DEBUG_COLUMN_CACHE
  pMem->iTabColHash = 0;
#endif
}
#endif /* SQLITE_DEBUG */


/*
** Make an shallow copy of pFrom into pTo.  Prior contents of
** pTo are freed.  The pFrom->z field is not duplicated.  If
** pFrom->z is used, then pTo->z points to the same thing as pFrom->z
** and flags gets srcType (either MEM_Ephem or MEM_Static).
*/
static SQLITE_NOINLINE void vdbeClrCopy(Mem *pTo, const Mem *pFrom, int eType){
  vdbeMemClearExternAndSetNull(pTo);
  assert( !VdbeMemDynamic(pTo) );
  sqlite3VdbeMemShallowCopy(pTo, pFrom, eType);
}
void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
  assert( (pFrom->flags & MEM_RowSet)==0 );
  assert( pTo->db==pFrom->db );
  if( VdbeMemDynamic(pTo) ){ vdbeClrCopy(pTo,pFrom,srcType); return; }
  memcpy(pTo, pFrom, MEMCELLSIZE);
#ifdef SQLITE_DEBUG_COLUMNCACHE
  pTo->iTabColHash = pFrom->iTabColHash;
#endif
  if( (pFrom->flags&MEM_Static)==0 ){
    pTo->flags &= ~(MEM_Dyn|MEM_Static|MEM_Ephem);
    assert( srcType==MEM_Ephem || srcType==MEM_Static );
    pTo->flags |= srcType;
  }
}

/*
** Make a full copy of pFrom into pTo.  Prior contents of pTo are
** freed before the copy is made.
*/
int sqlite3VdbeMemCopy(Mem *pTo, const Mem *pFrom){
  int rc = SQLITE_OK;

  assert( (pFrom->flags & MEM_RowSet)==0 );
  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
  memcpy(pTo, pFrom, MEMCELLSIZE);
#ifdef SQLITE_DEBUG_COLUMNCACHE
  pTo->iTabColHash = pFrom->iTabColHash;
#endif
  pTo->flags &= ~MEM_Dyn;
  if( pTo->flags&(MEM_Str|MEM_Blob) ){
    if( 0==(pFrom->flags&MEM_Static) ){
      pTo->flags |= MEM_Ephem;
      rc = sqlite3VdbeMemMakeWriteable(pTo);
    }
  }