/ Check-in [4e437844]
Login

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Improved interface to the Mem object handling. Small size reduction and performance increase.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | micro-optimizations
Files: files | file ages | folders
SHA1:4e437844322cc20eef92928b53fa6b37eded586e
User & Date: drh 2014-09-17 14:52:46
Context
2014-09-17
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
2014-09-16
21:54
Continuing cleanup of memory register memory allocation handling. check-in: 2598aedc user: drh tags: micro-optimizations
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/vdbe.c.

636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
....
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
....
2103
2104
2105
2106
2107
2108
2109
2110
2111

2112
2113
2114
2115
2116
2117
2118
2119
2120
....
2121
2122
2123
2124
2125
2126
2127
2128
2129

2130
2131
2132
2133
2134
2135
2136
2137
2138
....
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
    */
    assert( pOp->opflags==sqlite3OpcodeProperty[pOp->opcode] );
    if( pOp->opflags & OPFLG_OUT2_PRERELEASE ){
      assert( pOp->p2>0 );
      assert( pOp->p2<=(p->nMem-p->nCursor) );
      pOut = &aMem[pOp->p2];
      memAboutToChange(p, pOut);
      VdbeMemReleaseExtern(pOut);
      pOut->flags = MEM_Int;
    }

    /* Sanity checking on other operands */
#ifdef SQLITE_DEBUG
    if( (pOp->opflags & OPFLG_IN1)!=0 ){
      assert( pOp->p1>0 );
................................................................................
  u16 nullFlag;
  cnt = pOp->p3-pOp->p2;
  assert( pOp->p3<=(p->nMem-p->nCursor) );
  pOut->flags = nullFlag = pOp->p1 ? (MEM_Null|MEM_Cleared) : MEM_Null;
  while( cnt>0 ){
    pOut++;
    memAboutToChange(p, pOut);
    VdbeMemReleaseExtern(pOut);
    pOut->flags = nullFlag;
    cnt--;
  }
  break;
}

/* Opcode: SoftNull P1 * * * *
................................................................................
** Interpret the value in register P1 as a boolean value.  Store the
** boolean complement in register P2.  If the value in register P1 is 
** NULL, then a NULL is stored in P2.
*/
case OP_Not: {                /* same as TK_NOT, in1, out2 */
  pIn1 = &aMem[pOp->p1];
  pOut = &aMem[pOp->p2];
  if( pIn1->flags & MEM_Null ){
    sqlite3VdbeMemSetNull(pOut);

  }else{
    sqlite3VdbeMemSetInt64(pOut, !sqlite3VdbeIntValue(pIn1));
  }
  break;
}

/* Opcode: BitNot P1 P2 * * *
** Synopsis: r[P1]= ~r[P1]
**
................................................................................
** Interpret the content of register P1 as an integer.  Store the
** ones-complement of the P1 value into register P2.  If P1 holds
** a NULL then store a NULL in P2.
*/
case OP_BitNot: {             /* same as TK_BITNOT, in1, out2 */
  pIn1 = &aMem[pOp->p1];
  pOut = &aMem[pOp->p2];
  if( pIn1->flags & MEM_Null ){
    sqlite3VdbeMemSetNull(pOut);

  }else{
    sqlite3VdbeMemSetInt64(pOut, ~sqlite3VdbeIntValue(pIn1));
  }
  break;
}

/* Opcode: Once P1 P2 * * *
**
** Check the "once" flag number P1. If it is set, jump to instruction P2. 
................................................................................
  /* Extract the content for the p2+1-th column.  Control can only
  ** reach this point if aOffset[p2], aOffset[p2+1], and aType[p2] are
  ** all valid.
  */
  assert( p2<pC->nHdrParsed );
  assert( rc==SQLITE_OK );
  assert( sqlite3VdbeCheckMemInvariants(pDest) );
  VdbeMemReleaseExtern(pDest);
  if( pC->szRow>=aOffset[p2+1] ){
    /* This is the common case where the desired content fits on the original
    ** page - where the content is not on an overflow page */
    sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], aType[p2], pDest);
  }else{
    /* This branch happens only when content is on overflow pages */
    t = aType[p2];







|







 







|







 







<
|
>
|
|







 







<
|
>
|
|







 







|







636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
....
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
....
2103
2104
2105
2106
2107
2108
2109

2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
....
2121
2122
2123
2124
2125
2126
2127

2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
....
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
    */
    assert( pOp->opflags==sqlite3OpcodeProperty[pOp->opcode] );
    if( pOp->opflags & OPFLG_OUT2_PRERELEASE ){
      assert( pOp->p2>0 );
      assert( pOp->p2<=(p->nMem-p->nCursor) );
      pOut = &aMem[pOp->p2];
      memAboutToChange(p, pOut);
      if( VdbeMemDynamic(pOut) ) sqlite3VdbeMemSetNull(pOut);
      pOut->flags = MEM_Int;
    }

    /* Sanity checking on other operands */
#ifdef SQLITE_DEBUG
    if( (pOp->opflags & OPFLG_IN1)!=0 ){
      assert( pOp->p1>0 );
................................................................................
  u16 nullFlag;
  cnt = pOp->p3-pOp->p2;
  assert( pOp->p3<=(p->nMem-p->nCursor) );
  pOut->flags = nullFlag = pOp->p1 ? (MEM_Null|MEM_Cleared) : MEM_Null;
  while( cnt>0 ){
    pOut++;
    memAboutToChange(p, pOut);
    sqlite3VdbeMemSetNull(pOut);
    pOut->flags = nullFlag;
    cnt--;
  }
  break;
}

/* Opcode: SoftNull P1 * * * *
................................................................................
** Interpret the value in register P1 as a boolean value.  Store the
** boolean complement in register P2.  If the value in register P1 is 
** NULL, then a NULL is stored in P2.
*/
case OP_Not: {                /* same as TK_NOT, in1, out2 */
  pIn1 = &aMem[pOp->p1];
  pOut = &aMem[pOp->p2];

  sqlite3VdbeMemSetNull(pOut);
  if( (pIn1->flags & MEM_Null)==0 ){
    pOut->flags = MEM_Int;
    pOut->u.i = !sqlite3VdbeIntValue(pIn1);
  }
  break;
}

/* Opcode: BitNot P1 P2 * * *
** Synopsis: r[P1]= ~r[P1]
**
................................................................................
** Interpret the content of register P1 as an integer.  Store the
** ones-complement of the P1 value into register P2.  If P1 holds
** a NULL then store a NULL in P2.
*/
case OP_BitNot: {             /* same as TK_BITNOT, in1, out2 */
  pIn1 = &aMem[pOp->p1];
  pOut = &aMem[pOp->p2];

  sqlite3VdbeMemSetNull(pOut);
  if( (pIn1->flags & MEM_Null)==0 ){
    pOut->flags = MEM_Int;
    pOut->u.i = ~sqlite3VdbeIntValue(pIn1);
  }
  break;
}

/* Opcode: Once P1 P2 * * *
**
** Check the "once" flag number P1. If it is set, jump to instruction P2. 
................................................................................
  /* Extract the content for the p2+1-th column.  Control can only
  ** reach this point if aOffset[p2], aOffset[p2+1], and aType[p2] are
  ** all valid.
  */
  assert( p2<pC->nHdrParsed );
  assert( rc==SQLITE_OK );
  assert( sqlite3VdbeCheckMemInvariants(pDest) );
  if( VdbeMemDynamic(pDest) ) sqlite3VdbeMemSetNull(pDest);
  if( pC->szRow>=aOffset[p2+1] ){
    /* This is the common case where the desired content fits on the original
    ** page - where the content is not on an overflow page */
    sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], aType[p2], pDest);
  }else{
    /* This branch happens only when content is on overflow pages */
    t = aType[p2];

Changes to src/vdbeInt.h.

425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
double sqlite3VdbeRealValue(Mem*);
void sqlite3VdbeIntegerAffinity(Mem*);
int sqlite3VdbeMemRealify(Mem*);
int sqlite3VdbeMemNumerify(Mem*);
void sqlite3VdbeMemCast(Mem*,u8,u8);
int sqlite3VdbeMemFromBtree(BtCursor*,u32,u32,int,Mem*);
void sqlite3VdbeMemRelease(Mem *p);
void sqlite3VdbeMemReleaseExternal(Mem *p);
#define VdbeMemDynamic(X)  \
  (((X)->flags&(MEM_Agg|MEM_Dyn|MEM_RowSet|MEM_Frame))!=0)
#define VdbeMemReleaseExtern(X)  \
  if( VdbeMemDynamic(X) ) sqlite3VdbeMemReleaseExternal(X);
int sqlite3VdbeMemFinalize(Mem*, FuncDef*);
const char *sqlite3OpcodeName(int);
int sqlite3VdbeMemGrow(Mem *pMem, int n, int preserve);
int sqlite3VdbeCloseStatement(Vdbe *, int);
void sqlite3VdbeFrameDelete(VdbeFrame*);
int sqlite3VdbeFrameRestore(VdbeFrame *);
int sqlite3VdbeTransferError(Vdbe *p);







<


<
<







425
426
427
428
429
430
431

432
433


434
435
436
437
438
439
440
double sqlite3VdbeRealValue(Mem*);
void sqlite3VdbeIntegerAffinity(Mem*);
int sqlite3VdbeMemRealify(Mem*);
int sqlite3VdbeMemNumerify(Mem*);
void sqlite3VdbeMemCast(Mem*,u8,u8);
int sqlite3VdbeMemFromBtree(BtCursor*,u32,u32,int,Mem*);
void sqlite3VdbeMemRelease(Mem *p);

#define VdbeMemDynamic(X)  \
  (((X)->flags&(MEM_Agg|MEM_Dyn|MEM_RowSet|MEM_Frame))!=0)


int sqlite3VdbeMemFinalize(Mem*, FuncDef*);
const char *sqlite3OpcodeName(int);
int sqlite3VdbeMemGrow(Mem *pMem, int n, int preserve);
int sqlite3VdbeCloseStatement(Vdbe *, int);
void sqlite3VdbeFrameDelete(VdbeFrame*);
int sqlite3VdbeFrameRestore(VdbeFrame *);
int sqlite3VdbeTransferError(Vdbe *p);

Changes to src/vdbeapi.c.

658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
** Create a new aggregate context for p and return a pointer to
** its pMem->z element.
*/
static SQLITE_NOINLINE void *createAggContext(sqlite3_context *p, int nByte){
  Mem *pMem = p->pMem;
  assert( (pMem->flags & MEM_Agg)==0 );
  if( nByte<=0 ){
    sqlite3VdbeMemReleaseExternal(pMem);
    pMem->flags = MEM_Null;
    pMem->z = 0;
  }else{
    sqlite3VdbeMemGrow(pMem, nByte, 0);
    pMem->flags = MEM_Agg;
    pMem->u.pDef = p->pFunc;
    if( pMem->z ){
      memset(pMem->z, 0, nByte);







|
<







658
659
660
661
662
663
664
665

666
667
668
669
670
671
672
** Create a new aggregate context for p and return a pointer to
** its pMem->z element.
*/
static SQLITE_NOINLINE void *createAggContext(sqlite3_context *p, int nByte){
  Mem *pMem = p->pMem;
  assert( (pMem->flags & MEM_Agg)==0 );
  if( nByte<=0 ){
    sqlite3VdbeMemSetNull(pMem);

    pMem->z = 0;
  }else{
    sqlite3VdbeMemGrow(pMem, nByte, 0);
    pMem->flags = MEM_Agg;
    pMem->u.pDef = p->pFunc;
    if( pMem->z ){
      memset(pMem->z, 0, nByte);

Changes to src/vdbemem.c.

44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
...
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
...
307
308
309
310
311
312
313
314

315
316
317
318
319
320
321
322
323
324

325

326
327
328
329

330
331
332
333
334
335
336
337
...
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368


369

370
371
372
373
374
375
376
377
378
379
380
381
382
383
...
586
587
588
589
590
591
592









593
594
595
596
597
598
599
600
601
602
603
...
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
...
649
650
651
652
653
654
655
656
657
658
659

660
661
662
663
664
665
666
...
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
...
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
...
828
829
830
831
832
833
834
835

836
837
838
839
840
841
842
    assert( 
      ((p->z==p->zMalloc)? 1 : 0) +
      ((p->flags&MEM_Dyn)!=0 ? 1 : 0) +
      ((p->flags&MEM_Ephem)!=0 ? 1 : 0) +
      ((p->flags&MEM_Static)!=0 ? 1 : 0) == 1
    );
  }

  return 1;
}
#endif


/*
** If pMem is an object with a valid string representation, this routine
................................................................................
      pMem->z = pMem->zMalloc = sqlite3DbReallocOrFree(pMem->db, pMem->z, n);
      bPreserve = 0;
    }else{
      sqlite3DbFree(pMem->db, pMem->zMalloc);
      pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, n);
    }
    if( pMem->zMalloc==0 ){
      VdbeMemReleaseExtern(pMem);
      pMem->z = 0;
      pMem->flags = MEM_Null;  
      return SQLITE_NOMEM;
    }
  }

  if( pMem->z && bPreserve && pMem->z!=pMem->zMalloc ){
    memcpy(pMem->zMalloc, pMem->z, pMem->n);
  }
................................................................................
    rc = ctx.isError;
  }
  return rc;
}

/*
** If the memory cell contains a value that must be freed by
** invoking an external callback, then free it now. 

**
** This routine does NOT do any of the following:
**    (1)  Set the Mem.flags field to a rational value.
**    (2)  Free memory held by Mem.zMalloc
** The caller is expected to take care of setting Mem.flags appropriately.
**
** The VdbeMemReleaseExtern() macro invokes this routine if only if there
** is work for this routine to do.
*/
void sqlite3VdbeMemReleaseExternal(Mem *p){

  assert( p->db==0 || sqlite3_mutex_held(p->db->mutex) );

  if( p->flags&MEM_Agg ){
    sqlite3VdbeMemFinalize(p, p->u.pDef);
    assert( (p->flags & MEM_Agg)==0 );
    sqlite3VdbeMemRelease(p);

  }else 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 ){
................................................................................
}

/*
** Release memory held by the Mem p, both external memory cleared
** by p->xDel and memory in p->zMalloc.
**
** This is a helper routine invoked by sqlite3VdbeMemRelease() in
** the uncommon case when there really is memory in p that needs
** to be freeing.
*/
static SQLITE_NOINLINE void vdbeMemRelease(Mem *p){
  if( VdbeMemDynamic(p) ){
    sqlite3VdbeMemReleaseExternal(p);
  }
  if( p->zMalloc ){
    sqlite3DbFree(p->db, p->zMalloc);
    p->zMalloc = 0;
  }
  p->z = 0;
}

/*
** Release any memory held by the Mem. This may leave the Mem.flags in an
** inconsistent state, for example with (Mem.z==0) and (Mem.flags==MEM_Str).
**
** This routine releases both the Mem.xDel space and the Mem.zMalloc space.


** Use sqlite3VdbeMemReleaseExternal() to release just the Mem.xDel space.

*/
void sqlite3VdbeMemRelease(Mem *p){
  assert( sqlite3VdbeCheckMemInvariants(p) );
  if( VdbeMemDynamic(p) || p->zMalloc ){
    vdbeMemRelease(p);
  }else{
    p->z = 0;
  }
  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
................................................................................
    }
  }
}


/*
** Delete any previous value and set the value stored in *pMem to NULL.









*/
void sqlite3VdbeMemSetNull(Mem *pMem){
  if( VdbeMemDynamic(pMem) ){
    sqlite3VdbeMemReleaseExternal(pMem);
  }else{
    pMem->flags = MEM_Null;
  }
}
void sqlite3ValueSetNull(sqlite3_value *p){
  sqlite3VdbeMemSetNull((Mem*)p); 
}
................................................................................
void sqlite3VdbeMemSetZeroBlob(Mem *pMem, int n){
  sqlite3VdbeMemRelease(pMem);
  pMem->flags = MEM_Blob|MEM_Zero;
  pMem->n = 0;
  if( n<0 ) n = 0;
  pMem->u.nZero = n;
  pMem->enc = SQLITE_UTF8;

#ifdef SQLITE_OMIT_INCRBLOB
  sqlite3VdbeMemGrow(pMem, n, 0);
  if( pMem->z ){
    pMem->n = n;
    memset(pMem->z, 0, n);
  }
#endif
}

/*
** The pMem is known to contain content that needs to be destroyed prior
** to a value change.  So invoke the destructor, then set the value to
** a 64-bit integer.
*/
static SQLITE_NOINLINE void vdbeReleaseAndSetInt64(Mem *pMem, i64 val){
  sqlite3VdbeMemReleaseExternal(pMem);
  pMem->u.i = val;
  pMem->flags = MEM_Int;
}

/*
** Delete any previous value and set the value stored in *pMem to val,
** manifest type INTEGER.
................................................................................

#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** Delete any previous value and set the value stored in *pMem to val,
** manifest type REAL.
*/
void sqlite3VdbeMemSetDouble(Mem *pMem, double val){
  if( sqlite3IsNaN(val) ){
    sqlite3VdbeMemSetNull(pMem);
  }else{
    sqlite3VdbeMemRelease(pMem);

    pMem->r = val;
    pMem->flags = MEM_Real;
  }
}
#endif

/*
................................................................................
** 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).
*/
void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
  assert( (pFrom->flags & MEM_RowSet)==0 );
  assert( pTo->db==pFrom->db );
  VdbeMemReleaseExtern(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;
  }
................................................................................
** freed before the copy is made.
*/
int sqlite3VdbeMemCopy(Mem *pTo, const Mem *pFrom){
  int rc = SQLITE_OK;

  assert( pTo->db==pFrom->db );
  assert( (pFrom->flags & MEM_RowSet)==0 );
  VdbeMemReleaseExtern(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;
................................................................................
  }else{
    iLimit = SQLITE_MAX_LENGTH;
  }
  flags = (enc==0?MEM_Blob:MEM_Str);
  if( nByte<0 ){
    assert( enc!=0 );
    if( enc==SQLITE_UTF8 ){
      for(nByte=0; nByte<=iLimit && z[nByte]; nByte++){}

    }else{
      for(nByte=0; nByte<=iLimit && (z[nByte] | z[nByte+1]); nByte+=2){}
    }
    flags |= MEM_Term;
  }

  /* The following block sets the new values of Mem.z and Mem.xDel. It







<







 







|

<







 







|
>

<
|
|
|
<
<
<

<
>

>



|
>
|







 







|
|

|

|









|
|

|
>
>
|
>




|
<
<







 







>
>
>
>
>
>
>
>
>



|







 







<
<
<
|
<
<
<
<








|







 







<
|
<
<
>







 







|







 







|







 







|
>







44
45
46
47
48
49
50

51
52
53
54
55
56
57
...
116
117
118
119
120
121
122
123
124

125
126
127
128
129
130
131
...
305
306
307
308
309
310
311
312
313
314

315
316
317



318

319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
...
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374


375
376
377
378
379
380
381
...
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
...
616
617
618
619
620
621
622



623




624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
...
649
650
651
652
653
654
655

656


657
658
659
660
661
662
663
664
...
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
...
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
...
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
    assert( 
      ((p->z==p->zMalloc)? 1 : 0) +
      ((p->flags&MEM_Dyn)!=0 ? 1 : 0) +
      ((p->flags&MEM_Ephem)!=0 ? 1 : 0) +
      ((p->flags&MEM_Static)!=0 ? 1 : 0) == 1
    );
  }

  return 1;
}
#endif


/*
** If pMem is an object with a valid string representation, this routine
................................................................................
      pMem->z = pMem->zMalloc = sqlite3DbReallocOrFree(pMem->db, pMem->z, n);
      bPreserve = 0;
    }else{
      sqlite3DbFree(pMem->db, pMem->zMalloc);
      pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, n);
    }
    if( pMem->zMalloc==0 ){
      sqlite3VdbeMemSetNull(pMem);
      pMem->z = 0;

      return SQLITE_NOMEM;
    }
  }

  if( pMem->z && bPreserve && pMem->z!=pMem->zMalloc ){
    memcpy(pMem->zMalloc, pMem->z, pMem->n);
  }
................................................................................
    rc = ctx.isError;
  }
  return rc;
}

/*
** If the memory cell contains a value that must be freed by
** invoking the external callback in Mem.xDel, then this routine
** will free that value.  It also sets Mem.flags to MEM_Null.
**

** This is a helper routine for sqlite3VdbeMemSetNull() and
** for sqlite3VdbeMemRelease().  Use those other routines as the
** entry point for releasing Mem resources.



*/

static SQLITE_NOINLINE void vdbeMemClearExternAndSetNull(Mem *p){
  assert( p->db==0 || sqlite3_mutex_held(p->db->mutex) );
  assert( VdbeMemDynamic(p) );
  if( p->flags&MEM_Agg ){
    sqlite3VdbeMemFinalize(p, p->u.pDef);
    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 ){
................................................................................
}

/*
** Release memory held by the Mem p, both external memory cleared
** by p->xDel and memory in p->zMalloc.
**
** This is a helper routine invoked by sqlite3VdbeMemRelease() in
** the unusual case where there really is memory in p that needs
** to be freed.
*/
static SQLITE_NOINLINE void vdbeMemClear(Mem *p){
  if( VdbeMemDynamic(p) ){
    vdbeMemClearExternAndSetNull(p);
  }
  if( p->zMalloc ){
    sqlite3DbFree(p->db, p->zMalloc);
    p->zMalloc = 0;
  }
  p->z = 0;
}

/*
** Release any memory resources held by the Mem.  Both the memory that is
** free by Mem.xDel and the Mem.zMalloc allocation are freed.
**
** Use this routine prior to clean up prior to abandoning a Mem, or to
** reset a Mem back to its minimum memory utilization.
**
** Use sqlite3VdbeMemSetNull() to release just the Mem.xDel space
** 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
................................................................................
    }
  }
}


/*
** 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
** routine to invoke the destructor and deallocates Mem.zMalloc.
**
** Use this routine to reset the Mem prior to insert a new value.
**
** Use sqlite3VdbeMemRelease() to complete erase the Mem prior to abandoning it.
*/
void sqlite3VdbeMemSetNull(Mem *pMem){
  if( VdbeMemDynamic(pMem) ){
    vdbeMemClearExternAndSetNull(pMem);
  }else{
    pMem->flags = MEM_Null;
  }
}
void sqlite3ValueSetNull(sqlite3_value *p){
  sqlite3VdbeMemSetNull((Mem*)p); 
}
................................................................................
void sqlite3VdbeMemSetZeroBlob(Mem *pMem, int n){
  sqlite3VdbeMemRelease(pMem);
  pMem->flags = MEM_Blob|MEM_Zero;
  pMem->n = 0;
  if( n<0 ) n = 0;
  pMem->u.nZero = n;
  pMem->enc = SQLITE_UTF8;



  pMem->z = 0;




}

/*
** The pMem is known to contain content that needs to be destroyed prior
** to a value change.  So invoke the destructor, then set the value to
** a 64-bit integer.
*/
static SQLITE_NOINLINE void vdbeReleaseAndSetInt64(Mem *pMem, i64 val){
  sqlite3VdbeMemSetNull(pMem);
  pMem->u.i = val;
  pMem->flags = MEM_Int;
}

/*
** Delete any previous value and set the value stored in *pMem to val,
** manifest type INTEGER.
................................................................................

#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** Delete any previous value and set the value stored in *pMem to val,
** manifest type REAL.
*/
void sqlite3VdbeMemSetDouble(Mem *pMem, double val){

  sqlite3VdbeMemSetNull(pMem);


  if( !sqlite3IsNaN(val) ){
    pMem->r = val;
    pMem->flags = MEM_Real;
  }
}
#endif

/*
................................................................................
** 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).
*/
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;
  }
................................................................................
** freed before the copy is made.
*/
int sqlite3VdbeMemCopy(Mem *pTo, const Mem *pFrom){
  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;
................................................................................
  }else{
    iLimit = SQLITE_MAX_LENGTH;
  }
  flags = (enc==0?MEM_Blob:MEM_Str);
  if( nByte<0 ){
    assert( enc!=0 );
    if( enc==SQLITE_UTF8 ){
      nByte = sqlite3Strlen30(z);
      if( nByte>iLimit ) nByte = iLimit+1;
    }else{
      for(nByte=0; nByte<=iLimit && (z[nByte] | z[nByte+1]); nByte+=2){}
    }
    flags |= MEM_Term;
  }

  /* The following block sets the new values of Mem.z and Mem.xDel. It