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Overview
Comment:In the Mem object, stop requiring that Mem.xDel be NULL when the MEM_Dyn bit is clear. Also reduce the amount of initialization of Mem objects. All for a small size reduction and performance increase.
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SHA1: fdddb477c89dabb9f7bf2d5ccb32534868df3a03
User & Date: drh 2014-09-17 16:41:15
Context
2014-09-17
23:37
Performance improvement and slight size reduction to the comparison operators in the VDBE. check-in: 14052a7d user: drh tags: micro-optimizations
16:41
In the Mem object, stop requiring that Mem.xDel be NULL when the MEM_Dyn bit is clear. Also reduce the amount of initialization of Mem objects. All for a small size reduction and performance increase. check-in: fdddb477 user: drh tags: micro-optimizations
14:52
Improved interface to the Mem object handling. Small size reduction and performance increase. check-in: 4e437844 user: drh tags: micro-optimizations
Changes
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Changes to src/vdbe.c.

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    memcpy(pOut, pIn1, sizeof(Mem));
#ifdef SQLITE_DEBUG
    if( pOut->pScopyFrom>=&aMem[p1] && pOut->pScopyFrom<&aMem[p1+pOp->p3] ){
      pOut->pScopyFrom += p1 - pOp->p2;
    }
#endif
    pIn1->flags = MEM_Undefined;
    pIn1->xDel = 0;
    pIn1->zMalloc = zMalloc;
    REGISTER_TRACE(p2++, pOut);
    pIn1++;
    pOut++;
  }while( --n );
  break;
}
................................................................................
  }while( (++pRec)<=pLast );
  assert( i==nHdr );
  assert( j==nByte );

  assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
  pOut->n = (int)nByte;
  pOut->flags = MEM_Blob;
  pOut->xDel = 0;
  if( nZero ){
    pOut->u.nZero = nZero;
    pOut->flags |= MEM_Zero;
  }
  pOut->enc = SQLITE_UTF8;  /* In case the blob is ever converted to text */
  REGISTER_TRACE(pOp->p3, pOut);
  UPDATE_MAX_BLOBSIZE(pOut);
................................................................................
  pOut->flags = MEM_Null;
  rc = sqlite3VdbeCursorMoveto(pC);
  if( NEVER(rc) ) goto abort_due_to_error;
  assert( pC->deferredMoveto==0 );
  assert( pC->isTable==0 );
  if( !pC->nullRow ){
    rowid = 0;  /* Not needed.  Only used to silence a warning. */
    rc = sqlite3VdbeIdxRowid(pCrsr, &rowid);
    if( rc!=SQLITE_OK ){
      goto abort_due_to_error;
    }
    pOut->u.i = rowid;
    pOut->flags = MEM_Int;
  }
  break;
................................................................................
    r.default_rc = 0;
  }
  r.aMem = &aMem[pOp->p3];
#ifdef SQLITE_DEBUG
  { int i; for(i=0; i<r.nField; i++) assert( memIsValid(&r.aMem[i]) ); }
#endif
  res = 0;  /* Not needed.  Only used to silence a warning. */
  rc = sqlite3VdbeIdxKeyCompare(pC, &r, &res);
  assert( (OP_IdxLE&1)==(OP_IdxLT&1) && (OP_IdxGE&1)==(OP_IdxGT&1) );
  if( (pOp->opcode&1)==(OP_IdxLT&1) ){
    assert( pOp->opcode==OP_IdxLE || pOp->opcode==OP_IdxLT );
    res = -res;
  }else{
    assert( pOp->opcode==OP_IdxGE || pOp->opcode==OP_IdxGT );
    res++;
................................................................................
    apVal[i] = pRec;
    memAboutToChange(p, pRec);
  }
  ctx.pFunc = pOp->p4.pFunc;
  assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
  ctx.pMem = pMem = &aMem[pOp->p3];
  pMem->n++;
  t.flags = MEM_Null;
  t.z = 0;
  t.zMalloc = 0;
  t.xDel = 0;
  t.db = db;
  ctx.pOut = &t;
  ctx.isError = 0;
  ctx.pColl = 0;
  ctx.skipFlag = 0;
  if( ctx.pFunc->funcFlags & SQLITE_FUNC_NEEDCOLL ){
    assert( pOp>p->aOp );
    assert( pOp[-1].p4type==P4_COLLSEQ );







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    memcpy(pOut, pIn1, sizeof(Mem));
#ifdef SQLITE_DEBUG
    if( pOut->pScopyFrom>=&aMem[p1] && pOut->pScopyFrom<&aMem[p1+pOp->p3] ){
      pOut->pScopyFrom += p1 - pOp->p2;
    }
#endif
    pIn1->flags = MEM_Undefined;

    pIn1->zMalloc = zMalloc;
    REGISTER_TRACE(p2++, pOut);
    pIn1++;
    pOut++;
  }while( --n );
  break;
}
................................................................................
  }while( (++pRec)<=pLast );
  assert( i==nHdr );
  assert( j==nByte );

  assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
  pOut->n = (int)nByte;
  pOut->flags = MEM_Blob;

  if( nZero ){
    pOut->u.nZero = nZero;
    pOut->flags |= MEM_Zero;
  }
  pOut->enc = SQLITE_UTF8;  /* In case the blob is ever converted to text */
  REGISTER_TRACE(pOp->p3, pOut);
  UPDATE_MAX_BLOBSIZE(pOut);
................................................................................
  pOut->flags = MEM_Null;
  rc = sqlite3VdbeCursorMoveto(pC);
  if( NEVER(rc) ) goto abort_due_to_error;
  assert( pC->deferredMoveto==0 );
  assert( pC->isTable==0 );
  if( !pC->nullRow ){
    rowid = 0;  /* Not needed.  Only used to silence a warning. */
    rc = sqlite3VdbeIdxRowid(db, pCrsr, &rowid);
    if( rc!=SQLITE_OK ){
      goto abort_due_to_error;
    }
    pOut->u.i = rowid;
    pOut->flags = MEM_Int;
  }
  break;
................................................................................
    r.default_rc = 0;
  }
  r.aMem = &aMem[pOp->p3];
#ifdef SQLITE_DEBUG
  { int i; for(i=0; i<r.nField; i++) assert( memIsValid(&r.aMem[i]) ); }
#endif
  res = 0;  /* Not needed.  Only used to silence a warning. */
  rc = sqlite3VdbeIdxKeyCompare(db, pC, &r, &res);
  assert( (OP_IdxLE&1)==(OP_IdxLT&1) && (OP_IdxGE&1)==(OP_IdxGT&1) );
  if( (pOp->opcode&1)==(OP_IdxLT&1) ){
    assert( pOp->opcode==OP_IdxLE || pOp->opcode==OP_IdxLT );
    res = -res;
  }else{
    assert( pOp->opcode==OP_IdxGE || pOp->opcode==OP_IdxGT );
    res++;
................................................................................
    apVal[i] = pRec;
    memAboutToChange(p, pRec);
  }
  ctx.pFunc = pOp->p4.pFunc;
  assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
  ctx.pMem = pMem = &aMem[pOp->p3];
  pMem->n++;
  sqlite3VdbeMemInit(&t, db, MEM_Null);




  ctx.pOut = &t;
  ctx.isError = 0;
  ctx.pColl = 0;
  ctx.skipFlag = 0;
  if( ctx.pFunc->funcFlags & SQLITE_FUNC_NEEDCOLL ){
    assert( pOp>p->aOp );
    assert( pOp[-1].p4type==P4_COLLSEQ );

Changes to src/vdbeInt.h.

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  u8  enc;            /* SQLITE_UTF8, SQLITE_UTF16BE, SQLITE_UTF16LE */
  int n;              /* Number of characters in string value, excluding '\0' */
  double r;           /* Real value */
  char *z;            /* String or BLOB value */
  char *zMalloc;      /* Dynamic buffer allocated by sqlite3_malloc() */
  /* ShallowCopy only needs to copy the information above */
  sqlite3 *db;        /* The associated database connection */
  void (*xDel)(void*);/* If not null, call this function to delete Mem.z */
#ifdef SQLITE_DEBUG
  Mem *pScopyFrom;    /* This Mem is a shallow copy of pScopyFrom */
  void *pFiller;      /* So that sizeof(Mem) is a multiple of 8 */
#endif
};

/* One or more of the following flags are set to indicate the validOK
................................................................................
u32 sqlite3VdbeSerialTypeLen(u32);
u32 sqlite3VdbeSerialType(Mem*, int);
u32 sqlite3VdbeSerialPut(unsigned char*, Mem*, u32);
u32 sqlite3VdbeSerialGet(const unsigned char*, u32, Mem*);
void sqlite3VdbeDeleteAuxData(Vdbe*, int, int);

int sqlite2BtreeKeyCompare(BtCursor *, const void *, int, int, int *);
int sqlite3VdbeIdxKeyCompare(VdbeCursor*,UnpackedRecord*,int*);
int sqlite3VdbeIdxRowid(BtCursor *, i64 *);
int sqlite3VdbeExec(Vdbe*);
int sqlite3VdbeList(Vdbe*);
int sqlite3VdbeHalt(Vdbe*);
int sqlite3VdbeChangeEncoding(Mem *, int);
int sqlite3VdbeMemTooBig(Mem*);
int sqlite3VdbeMemCopy(Mem*, const Mem*);
void sqlite3VdbeMemShallowCopy(Mem*, const Mem*, int);
................................................................................
int sqlite3VdbeMemSetStr(Mem*, const char*, int, u8, void(*)(void*));
void sqlite3VdbeMemSetInt64(Mem*, i64);
#ifdef SQLITE_OMIT_FLOATING_POINT
# define sqlite3VdbeMemSetDouble sqlite3VdbeMemSetInt64
#else
  void sqlite3VdbeMemSetDouble(Mem*, double);
#endif

void sqlite3VdbeMemSetNull(Mem*);
void sqlite3VdbeMemSetZeroBlob(Mem*,int);
void sqlite3VdbeMemSetRowSet(Mem*);
int sqlite3VdbeMemMakeWriteable(Mem*);
int sqlite3VdbeMemStringify(Mem*, u8, u8);
i64 sqlite3VdbeIntValue(Mem*);
int sqlite3VdbeMemIntegerify(Mem*);







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  u8  enc;            /* SQLITE_UTF8, SQLITE_UTF16BE, SQLITE_UTF16LE */
  int n;              /* Number of characters in string value, excluding '\0' */
  double r;           /* Real value */
  char *z;            /* String or BLOB value */
  char *zMalloc;      /* Dynamic buffer allocated by sqlite3_malloc() */
  /* ShallowCopy only needs to copy the information above */
  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 */
  void *pFiller;      /* So that sizeof(Mem) is a multiple of 8 */
#endif
};

/* One or more of the following flags are set to indicate the validOK
................................................................................
u32 sqlite3VdbeSerialTypeLen(u32);
u32 sqlite3VdbeSerialType(Mem*, int);
u32 sqlite3VdbeSerialPut(unsigned char*, Mem*, u32);
u32 sqlite3VdbeSerialGet(const unsigned char*, u32, Mem*);
void sqlite3VdbeDeleteAuxData(Vdbe*, int, int);

int sqlite2BtreeKeyCompare(BtCursor *, const void *, int, int, int *);
int sqlite3VdbeIdxKeyCompare(sqlite3*,VdbeCursor*,UnpackedRecord*,int*);
int sqlite3VdbeIdxRowid(sqlite3*, BtCursor*, i64*);
int sqlite3VdbeExec(Vdbe*);
int sqlite3VdbeList(Vdbe*);
int sqlite3VdbeHalt(Vdbe*);
int sqlite3VdbeChangeEncoding(Mem *, int);
int sqlite3VdbeMemTooBig(Mem*);
int sqlite3VdbeMemCopy(Mem*, const Mem*);
void sqlite3VdbeMemShallowCopy(Mem*, const Mem*, int);
................................................................................
int sqlite3VdbeMemSetStr(Mem*, const char*, int, u8, void(*)(void*));
void sqlite3VdbeMemSetInt64(Mem*, i64);
#ifdef SQLITE_OMIT_FLOATING_POINT
# define sqlite3VdbeMemSetDouble sqlite3VdbeMemSetInt64
#else
  void sqlite3VdbeMemSetDouble(Mem*, double);
#endif
void sqlite3VdbeMemInit(Mem*,sqlite3*,u16);
void sqlite3VdbeMemSetNull(Mem*);
void sqlite3VdbeMemSetZeroBlob(Mem*,int);
void sqlite3VdbeMemSetRowSet(Mem*);
int sqlite3VdbeMemMakeWriteable(Mem*);
int sqlite3VdbeMemStringify(Mem*, u8, u8);
i64 sqlite3VdbeIntValue(Mem*);
int sqlite3VdbeMemIntegerify(Mem*);

Changes to src/vdbeaux.c.

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      pMem->flags = MEM_Int;
      return 0;
    }
    default: {
      static const u16 aFlag[] = { MEM_Blob|MEM_Ephem, MEM_Str|MEM_Ephem };
      pMem->z = (char *)buf;
      pMem->n = (serial_type-12)/2;
      pMem->xDel = 0;
      pMem->flags = aFlag[serial_type&1];
      return pMem->n;
    }
  }
  return 0;
}
/*
................................................................................
    const void *v1, *v2;
    int n1, n2;
    Mem c1;
    Mem c2;
    c1.db = c2.db = pMem1->db;
    c1.flags = c2.flags = 0;
    c1.zMalloc = c2.zMalloc = 0;
    c1.xDel = c2.xDel = 0;
    sqlite3VdbeMemShallowCopy(&c1, pMem1, MEM_Ephem);
    sqlite3VdbeMemShallowCopy(&c2, pMem2, MEM_Ephem);
    v1 = sqlite3ValueText((sqlite3_value*)&c1, pColl->enc);
    n1 = v1==0 ? 0 : c1.n;
    v2 = sqlite3ValueText((sqlite3_value*)&c2, pColl->enc);
    n2 = v2==0 ? 0 : c2.n;
    rc = pColl->xCmp(pColl->pUser, n1, v1, n2, v2);
................................................................................
** pCur points at an index entry created using the OP_MakeRecord opcode.
** Read the rowid (the last field in the record) and store it in *rowid.
** Return SQLITE_OK if everything works, or an error code otherwise.
**
** pCur might be pointing to text obtained from a corrupt database file.
** So the content cannot be trusted.  Do appropriate checks on the content.
*/
int sqlite3VdbeIdxRowid(BtCursor *pCur, i64 *rowid){
  i64 nCellKey = 0;
  int rc;
  u32 szHdr;        /* Size of the header */
  u32 typeRowid;    /* Serial type of the rowid */
  u32 lenRowid;     /* Size of the rowid */
  Mem m, v;

................................................................................
  */
  assert( sqlite3BtreeCursorIsValid(pCur) );
  VVA_ONLY(rc =) sqlite3BtreeKeySize(pCur, &nCellKey);
  assert( rc==SQLITE_OK );     /* pCur is always valid so KeySize cannot fail */
  assert( (nCellKey & SQLITE_MAX_U32)==(u64)nCellKey );

  /* Read in the complete content of the index entry */
  memset(&m, 0, sizeof(m));
  rc = sqlite3VdbeMemFromBtree(pCur, 0, (u32)nCellKey, 1, &m);
  if( rc ){
    return rc;
  }

  /* The index entry must begin with a header size */
  (void)getVarint32((u8*)m.z, szHdr);
................................................................................
**
** pUnpacked is either created without a rowid or is truncated so that it
** omits the rowid at the end.  The rowid at the end of the index entry
** is ignored as well.  Hence, this routine only compares the prefixes 
** of the keys prior to the final rowid, not the entire key.
*/
int sqlite3VdbeIdxKeyCompare(

  VdbeCursor *pC,                  /* The cursor to compare against */
  UnpackedRecord *pUnpacked,       /* Unpacked version of key */
  int *res                         /* Write the comparison result here */
){
  i64 nCellKey = 0;
  int rc;
  BtCursor *pCur = pC->pCursor;
................................................................................
  assert( rc==SQLITE_OK );    /* pCur is always valid so KeySize cannot fail */
  /* nCellKey will always be between 0 and 0xffffffff because of the way
  ** that btreeParseCellPtr() and sqlite3GetVarint32() are implemented */
  if( nCellKey<=0 || nCellKey>0x7fffffff ){
    *res = 0;
    return SQLITE_CORRUPT_BKPT;
  }
  memset(&m, 0, sizeof(m));
  rc = sqlite3VdbeMemFromBtree(pC->pCursor, 0, (u32)nCellKey, 1, &m);
  if( rc ){
    return rc;
  }
  *res = sqlite3VdbeRecordCompare(m.n, m.z, pUnpacked);
  sqlite3VdbeMemRelease(&m);
  return SQLITE_OK;







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      pMem->flags = MEM_Int;
      return 0;
    }
    default: {
      static const u16 aFlag[] = { MEM_Blob|MEM_Ephem, MEM_Str|MEM_Ephem };
      pMem->z = (char *)buf;
      pMem->n = (serial_type-12)/2;

      pMem->flags = aFlag[serial_type&1];
      return pMem->n;
    }
  }
  return 0;
}
/*
................................................................................
    const void *v1, *v2;
    int n1, n2;
    Mem c1;
    Mem c2;
    c1.db = c2.db = pMem1->db;
    c1.flags = c2.flags = 0;
    c1.zMalloc = c2.zMalloc = 0;

    sqlite3VdbeMemShallowCopy(&c1, pMem1, MEM_Ephem);
    sqlite3VdbeMemShallowCopy(&c2, pMem2, MEM_Ephem);
    v1 = sqlite3ValueText((sqlite3_value*)&c1, pColl->enc);
    n1 = v1==0 ? 0 : c1.n;
    v2 = sqlite3ValueText((sqlite3_value*)&c2, pColl->enc);
    n2 = v2==0 ? 0 : c2.n;
    rc = pColl->xCmp(pColl->pUser, n1, v1, n2, v2);
................................................................................
** pCur points at an index entry created using the OP_MakeRecord opcode.
** Read the rowid (the last field in the record) and store it in *rowid.
** Return SQLITE_OK if everything works, or an error code otherwise.
**
** pCur might be pointing to text obtained from a corrupt database file.
** So the content cannot be trusted.  Do appropriate checks on the content.
*/
int sqlite3VdbeIdxRowid(sqlite3 *db, BtCursor *pCur, i64 *rowid){
  i64 nCellKey = 0;
  int rc;
  u32 szHdr;        /* Size of the header */
  u32 typeRowid;    /* Serial type of the rowid */
  u32 lenRowid;     /* Size of the rowid */
  Mem m, v;

................................................................................
  */
  assert( sqlite3BtreeCursorIsValid(pCur) );
  VVA_ONLY(rc =) sqlite3BtreeKeySize(pCur, &nCellKey);
  assert( rc==SQLITE_OK );     /* pCur is always valid so KeySize cannot fail */
  assert( (nCellKey & SQLITE_MAX_U32)==(u64)nCellKey );

  /* Read in the complete content of the index entry */
  sqlite3VdbeMemInit(&m, db, 0);
  rc = sqlite3VdbeMemFromBtree(pCur, 0, (u32)nCellKey, 1, &m);
  if( rc ){
    return rc;
  }

  /* The index entry must begin with a header size */
  (void)getVarint32((u8*)m.z, szHdr);
................................................................................
**
** pUnpacked is either created without a rowid or is truncated so that it
** omits the rowid at the end.  The rowid at the end of the index entry
** is ignored as well.  Hence, this routine only compares the prefixes 
** of the keys prior to the final rowid, not the entire key.
*/
int sqlite3VdbeIdxKeyCompare(
  sqlite3 *db,                     /* Database connection */
  VdbeCursor *pC,                  /* The cursor to compare against */
  UnpackedRecord *pUnpacked,       /* Unpacked version of key */
  int *res                         /* Write the comparison result here */
){
  i64 nCellKey = 0;
  int rc;
  BtCursor *pCur = pC->pCursor;
................................................................................
  assert( rc==SQLITE_OK );    /* pCur is always valid so KeySize cannot fail */
  /* nCellKey will always be between 0 and 0xffffffff because of the way
  ** that btreeParseCellPtr() and sqlite3GetVarint32() are implemented */
  if( nCellKey<=0 || nCellKey>0x7fffffff ){
    *res = 0;
    return SQLITE_CORRUPT_BKPT;
  }
  sqlite3VdbeMemInit(&m, db, 0);
  rc = sqlite3VdbeMemFromBtree(pC->pCursor, 0, (u32)nCellKey, 1, &m);
  if( rc ){
    return rc;
  }
  *res = sqlite3VdbeRecordCompare(m.n, m.z, pUnpacked);
  sqlite3VdbeMemRelease(&m);
  return SQLITE_OK;

Changes to src/vdbemem.c.

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/*
** Check invariants on a Mem object.
**
** This routine is intended for use inside of assert() statements, like
** this:    assert( sqlite3VdbeCheckMemInvariants(pMem) );
*/
int sqlite3VdbeCheckMemInvariants(Mem *p){
  /* The MEM_Dyn bit is set if and only if Mem.xDel is a non-NULL destructor
  ** function for Mem.z 
  */
  assert( (p->flags & MEM_Dyn)==0 || p->xDel!=0 );
  assert( (p->flags & MEM_Dyn)!=0 || p->xDel==0 );

  /* If p holds a string or blob, the Mem.z must point to exactly
  ** one of the following:
  **
  **   (1) Memory in Mem.zMalloc and managed by the Mem object
  **   (2) Memory to be freed using Mem.xDel
  **   (3) An ephemeral string or blob
................................................................................
  if( (pMem->flags&MEM_Dyn)!=0 ){
    assert( pMem->xDel!=0 && pMem->xDel!=SQLITE_DYNAMIC );
    pMem->xDel((void *)(pMem->z));
  }

  pMem->z = pMem->zMalloc;
  pMem->flags &= ~(MEM_Dyn|MEM_Ephem|MEM_Static);
  pMem->xDel = 0;
  return SQLITE_OK;
}

/*
** Make the given Mem object MEM_Dyn.  In other words, make it so
** that any TEXT or BLOB content is stored in memory obtained from
** malloc().  In this way, we know that the memory is safe to be
................................................................................
    memset(&t, 0, sizeof(t));
    t.flags = MEM_Null;
    t.db = pMem->db;
    ctx.pOut = &t;
    ctx.pMem = pMem;
    ctx.pFunc = pFunc;
    pFunc->xFinalize(&ctx); /* IMP: R-24505-23230 */
    assert( 0==(pMem->flags&MEM_Dyn) && !pMem->xDel );
    sqlite3DbFree(pMem->db, pMem->zMalloc);
    memcpy(pMem, &t, sizeof(t));
    rc = ctx.isError;
  }
  return rc;
}

................................................................................
    assert( (p->flags & MEM_Agg)==0 );
    testcase( p->flags & MEM_Dyn );
  }
  if( p->flags&MEM_Dyn ){
    assert( (p->flags&MEM_RowSet)==0 );
    assert( p->xDel!=SQLITE_DYNAMIC && p->xDel!=0 );
    p->xDel((void *)p->z);
    p->xDel = 0;
  }else if( p->flags&MEM_RowSet ){
    sqlite3RowSetClear(p->u.pRowSet);
  }else if( p->flags&MEM_Frame ){
    VdbeFrame *pFrame = p->u.pFrame;
    pFrame->pParent = pFrame->v->pDelFrame;
    pFrame->v->pDelFrame = pFrame;
  }
................................................................................
** prior to inserting new content into the Mem.
*/
void sqlite3VdbeMemRelease(Mem *p){
  assert( sqlite3VdbeCheckMemInvariants(p) );
  if( VdbeMemDynamic(p) || p->zMalloc ){
    vdbeMemClear(p);
  }
  assert( p->xDel==0 );
}

/*
** Convert a 64-bit IEEE double into a 64-bit signed integer.
** If the double is out of range of a 64-bit signed integer then
** return the closest available 64-bit signed integer.
*/
................................................................................
      assert( pMem->flags & MEM_Str || pMem->db->mallocFailed );
      pMem->flags &= ~(MEM_Int|MEM_Real|MEM_Blob|MEM_Zero);
      break;
    }
  }
}














/*
** Delete any previous value and set the value stored in *pMem to NULL.
**
** This routine calls the Mem.xDel destructor to dispose of values that
** require the destructor.  But it preserves the Mem.zMalloc memory allocation.
** To free all resources, use sqlite3VdbeMemRelease(), which both calls this
................................................................................
** and flags gets srcType (either MEM_Ephem or MEM_Static).
*/
void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
  assert( (pFrom->flags & MEM_RowSet)==0 );
  assert( pTo->db==pFrom->db );
  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
  memcpy(pTo, pFrom, MEMCELLSIZE);
  assert( pTo->xDel==0 );
  if( (pFrom->flags&MEM_Static)==0 ){
    pTo->flags &= ~(MEM_Dyn|MEM_Static|MEM_Ephem);
    assert( srcType==MEM_Ephem || srcType==MEM_Static );
    pTo->flags |= srcType;
  }
}

................................................................................
  int rc = SQLITE_OK;

  assert( pTo->db==pFrom->db );
  assert( (pFrom->flags & MEM_RowSet)==0 );
  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
  memcpy(pTo, pFrom, MEMCELLSIZE);
  pTo->flags &= ~MEM_Dyn;
  assert( pTo->xDel==0 );

  if( pTo->flags&(MEM_Str|MEM_Blob) ){
    if( 0==(pFrom->flags&MEM_Static) ){
      pTo->flags |= MEM_Ephem;
      rc = sqlite3VdbeMemMakeWriteable(pTo);
    }
  }

................................................................................
  assert( pFrom->db==0 || sqlite3_mutex_held(pFrom->db->mutex) );
  assert( pTo->db==0 || sqlite3_mutex_held(pTo->db->mutex) );
  assert( pFrom->db==0 || pTo->db==0 || pFrom->db==pTo->db );

  sqlite3VdbeMemRelease(pTo);
  memcpy(pTo, pFrom, sizeof(Mem));
  pFrom->flags = MEM_Null;
  pFrom->xDel = 0;
  pFrom->zMalloc = 0;
}

/*
** Change the value of a Mem to be a string or a BLOB.
**
** The memory management strategy depends on the value of the xDel
................................................................................
    if( sqlite3VdbeMemGrow(pMem, nAlloc, 0) ){
      return SQLITE_NOMEM;
    }
    memcpy(pMem->z, z, nAlloc);
  }else if( xDel==SQLITE_DYNAMIC ){
    sqlite3VdbeMemRelease(pMem);
    pMem->zMalloc = pMem->z = (char *)z;
    pMem->xDel = 0;
  }else{
    sqlite3VdbeMemRelease(pMem);
    pMem->z = (char *)z;
    pMem->xDel = xDel;
    flags |= ((xDel==SQLITE_STATIC)?MEM_Static:MEM_Dyn);
  }

................................................................................
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  char *zData;        /* Data from the btree layer */
  u32 available = 0;  /* Number of bytes available on the local btree page */
  int rc = SQLITE_OK; /* Return code */

  assert( sqlite3BtreeCursorIsValid(pCur) );
  assert( pMem->xDel==0 );

  /* Note: the calls to BtreeKeyFetch() and DataFetch() below assert() 
  ** that both the BtShared and database handle mutexes are held. */
  assert( (pMem->flags & MEM_RowSet)==0 );
  if( key ){
    zData = (char *)sqlite3BtreeKeyFetch(pCur, &available);
  }else{
    zData = (char *)sqlite3BtreeDataFetch(pCur, &available);
  }
  assert( zData!=0 );

  if( offset+amt<=available ){
    sqlite3VdbeMemRelease(pMem);
    pMem->z = &zData[offset];
    pMem->flags = MEM_Blob|MEM_Ephem;
    pMem->n = (int)amt;
  }else{
    pMem->flags = MEM_Null;
    if( SQLITE_OK==(rc = sqlite3VdbeMemGrow(pMem, amt+2, 0)) ){
      if( key ){







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/*
** Check invariants on a Mem object.
**
** This routine is intended for use inside of assert() statements, like
** this:    assert( sqlite3VdbeCheckMemInvariants(pMem) );
*/
int sqlite3VdbeCheckMemInvariants(Mem *p){
  /* If MEM_Dyn is set then Mem.xDel!=0.  
  ** Mem.xDel is might not be initialized if MEM_Dyn is clear.
  */
  assert( (p->flags & MEM_Dyn)==0 || p->xDel!=0 );


  /* If p holds a string or blob, the Mem.z must point to exactly
  ** one of the following:
  **
  **   (1) Memory in Mem.zMalloc and managed by the Mem object
  **   (2) Memory to be freed using Mem.xDel
  **   (3) An ephemeral string or blob
................................................................................
  if( (pMem->flags&MEM_Dyn)!=0 ){
    assert( pMem->xDel!=0 && pMem->xDel!=SQLITE_DYNAMIC );
    pMem->xDel((void *)(pMem->z));
  }

  pMem->z = pMem->zMalloc;
  pMem->flags &= ~(MEM_Dyn|MEM_Ephem|MEM_Static);

  return SQLITE_OK;
}

/*
** Make the given Mem object MEM_Dyn.  In other words, make it so
** that any TEXT or BLOB content is stored in memory obtained from
** malloc().  In this way, we know that the memory is safe to be
................................................................................
    memset(&t, 0, sizeof(t));
    t.flags = MEM_Null;
    t.db = pMem->db;
    ctx.pOut = &t;
    ctx.pMem = pMem;
    ctx.pFunc = pFunc;
    pFunc->xFinalize(&ctx); /* IMP: R-24505-23230 */
    assert( (pMem->flags & MEM_Dyn)==0 );
    sqlite3DbFree(pMem->db, pMem->zMalloc);
    memcpy(pMem, &t, sizeof(t));
    rc = ctx.isError;
  }
  return rc;
}

................................................................................
    assert( (p->flags & MEM_Agg)==0 );
    testcase( p->flags & MEM_Dyn );
  }
  if( p->flags&MEM_Dyn ){
    assert( (p->flags&MEM_RowSet)==0 );
    assert( p->xDel!=SQLITE_DYNAMIC && p->xDel!=0 );
    p->xDel((void *)p->z);

  }else if( p->flags&MEM_RowSet ){
    sqlite3RowSetClear(p->u.pRowSet);
  }else if( p->flags&MEM_Frame ){
    VdbeFrame *pFrame = p->u.pFrame;
    pFrame->pParent = pFrame->v->pDelFrame;
    pFrame->v->pDelFrame = pFrame;
  }
................................................................................
** prior to inserting new content into the Mem.
*/
void sqlite3VdbeMemRelease(Mem *p){
  assert( sqlite3VdbeCheckMemInvariants(p) );
  if( VdbeMemDynamic(p) || p->zMalloc ){
    vdbeMemClear(p);
  }

}

/*
** Convert a 64-bit IEEE double into a 64-bit signed integer.
** If the double is out of range of a 64-bit signed integer then
** return the closest available 64-bit signed integer.
*/
................................................................................
      assert( pMem->flags & MEM_Str || pMem->db->mallocFailed );
      pMem->flags &= ~(MEM_Int|MEM_Real|MEM_Blob|MEM_Zero);
      break;
    }
  }
}

/*
** Initialize bulk memory to be a consistent Mem object.
**
** The minimum amount of initialization feasible is performed.
*/
void sqlite3VdbeMemInit(Mem *pMem, sqlite3 *db, u16 flags){
  assert( (flags & ~MEM_TypeMask)==0 );
  pMem->flags = flags;
  pMem->db = db;
  pMem->zMalloc = 0;
}


/*
** Delete any previous value and set the value stored in *pMem to NULL.
**
** This routine calls the Mem.xDel destructor to dispose of values that
** require the destructor.  But it preserves the Mem.zMalloc memory allocation.
** To free all resources, use sqlite3VdbeMemRelease(), which both calls this
................................................................................
** and flags gets srcType (either MEM_Ephem or MEM_Static).
*/
void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
  assert( (pFrom->flags & MEM_RowSet)==0 );
  assert( pTo->db==pFrom->db );
  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
  memcpy(pTo, pFrom, MEMCELLSIZE);

  if( (pFrom->flags&MEM_Static)==0 ){
    pTo->flags &= ~(MEM_Dyn|MEM_Static|MEM_Ephem);
    assert( srcType==MEM_Ephem || srcType==MEM_Static );
    pTo->flags |= srcType;
  }
}

................................................................................
  int rc = SQLITE_OK;

  assert( pTo->db==pFrom->db );
  assert( (pFrom->flags & MEM_RowSet)==0 );
  if( VdbeMemDynamic(pTo) ) vdbeMemClearExternAndSetNull(pTo);
  memcpy(pTo, pFrom, MEMCELLSIZE);
  pTo->flags &= ~MEM_Dyn;


  if( pTo->flags&(MEM_Str|MEM_Blob) ){
    if( 0==(pFrom->flags&MEM_Static) ){
      pTo->flags |= MEM_Ephem;
      rc = sqlite3VdbeMemMakeWriteable(pTo);
    }
  }

................................................................................
  assert( pFrom->db==0 || sqlite3_mutex_held(pFrom->db->mutex) );
  assert( pTo->db==0 || sqlite3_mutex_held(pTo->db->mutex) );
  assert( pFrom->db==0 || pTo->db==0 || pFrom->db==pTo->db );

  sqlite3VdbeMemRelease(pTo);
  memcpy(pTo, pFrom, sizeof(Mem));
  pFrom->flags = MEM_Null;

  pFrom->zMalloc = 0;
}

/*
** Change the value of a Mem to be a string or a BLOB.
**
** The memory management strategy depends on the value of the xDel
................................................................................
    if( sqlite3VdbeMemGrow(pMem, nAlloc, 0) ){
      return SQLITE_NOMEM;
    }
    memcpy(pMem->z, z, nAlloc);
  }else if( xDel==SQLITE_DYNAMIC ){
    sqlite3VdbeMemRelease(pMem);
    pMem->zMalloc = pMem->z = (char *)z;

  }else{
    sqlite3VdbeMemRelease(pMem);
    pMem->z = (char *)z;
    pMem->xDel = xDel;
    flags |= ((xDel==SQLITE_STATIC)?MEM_Static:MEM_Dyn);
  }

................................................................................
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  char *zData;        /* Data from the btree layer */
  u32 available = 0;  /* Number of bytes available on the local btree page */
  int rc = SQLITE_OK; /* Return code */

  assert( sqlite3BtreeCursorIsValid(pCur) );
  assert( !VdbeMemDynamic(pMem) );

  /* Note: the calls to BtreeKeyFetch() and DataFetch() below assert() 
  ** that both the BtShared and database handle mutexes are held. */
  assert( (pMem->flags & MEM_RowSet)==0 );
  if( key ){
    zData = (char *)sqlite3BtreeKeyFetch(pCur, &available);
  }else{
    zData = (char *)sqlite3BtreeDataFetch(pCur, &available);
  }
  assert( zData!=0 );

  if( offset+amt<=available ){

    pMem->z = &zData[offset];
    pMem->flags = MEM_Blob|MEM_Ephem;
    pMem->n = (int)amt;
  }else{
    pMem->flags = MEM_Null;
    if( SQLITE_OK==(rc = sqlite3VdbeMemGrow(pMem, amt+2, 0)) ){
      if( key ){