pMem->z = (char *)z;
  if( xDel==SQLITE_STATIC ){
    pMem->flags = MEM_Static;
  }else if( xDel==SQLITE_TRANSIENT ){
    pMem->flags = MEM_Ephem;
  }else{
    pMem->flags = MEM_Dyn;
    pMem->xDel = xDel;
  }

  pMem->enc = enc;
  pMem->type = enc==0 ? SQLITE_BLOB : SQLITE_TEXT;
  pMem->n = n;

  assert( enc==0 || enc==SQLITE_UTF8 || enc==SQLITE_UTF16LE 
      || enc==SQLITE_UTF16BE );
  switch( enc ){
    case 0:
      pMem->flags |= MEM_Blob;
      pMem->enc = SQLITE_UTF8;
      break;

    case SQLITE_UTF8:
      pMem->flags |= MEM_Str;
      if( n<0 ){
        pMem->n = strlen(z);
        pMem->flags |= MEM_Term;
      }
      break;

#ifndef SQLITE_OMIT_UTF16
    case SQLITE_UTF16LE:
    case SQLITE_UTF16BE:
      pMem->flags |= MEM_Str;
      if( pMem->n<0 ){
        pMem->n = sqlite3utf16ByteLen(pMem->z,-1);
        pMem->flags |= MEM_Term;
      }
      if( sqlite3VdbeMemHandleBom(pMem) ){
        return SQLITE_NOMEM;
      }
#endif /* SQLITE_OMIT_UTF16 */
  }
  if( pMem->flags&MEM_Ephem ){
    return sqlite3VdbeMemMakeWriteable(pMem);
  }
  return SQLITE_OK;
}

/*
** Compare the values contained by the two memory cells, returning
** negative, zero or positive if pMem1 is less than, equal to, or greater
** than pMem2. Sorting order is NULL's first, followed by numbers (integers
** and reals) sorted numerically, followed by text ordered by the collating
** sequence pColl and finally blob's ordered by memcmp().
**
** Two NULL values are considered equal by this function.
*/
int sqlite3MemCompare(const Mem *pMem1, const Mem *pMem2, const CollSeq *pColl){
  int rc;
  int f1, f2;
  int combined_flags;

  /* Interchange pMem1 and pMem2 if the collating sequence specifies
  ** DESC order.
  */
  f1 = pMem1->flags;
  f2 = pMem2->flags;
  combined_flags = f1|f2;
 
  /* If one value is NULL, it is less than the other. If both values
  ** are NULL, return 0.
  */
  if( combined_flags&MEM_Null ){
    return (f2&MEM_Null) - (f1&MEM_Null);
  }

  /* If one value is a number and the other is not, the number is less.
  ** If both are numbers, compare as reals if one is a real, or as integers
  ** if both values are integers.
  */
  if( combined_flags&(MEM_Int|MEM_Real) ){
    if( !(f1&(MEM_Int|MEM_Real)) ){
      return 1;
    }
    if( !(f2&(MEM_Int|MEM_Real)) ){
      return -1;
    }
    if( (f1 & f2 & MEM_Int)==0 ){
      double r1, r2;
      if( (f1&MEM_Real)==0 ){
        r1 = pMem1->i;
      }else{
        r1 = pMem1->r;
      }
      if( (f2&MEM_Real)==0 ){
        r2 = pMem2->i;
      }else{
        r2 = pMem2->r;
      }
      if( r1<r2 ) return -1;
      if( r1>r2 ) return 1;
      return 0;
    }else{
      assert( f1&MEM_Int );
      assert( f2&MEM_Int );
      if( pMem1->i < pMem2->i ) return -1;
      if( pMem1->i > pMem2->i ) return 1;
      return 0;
    }
  }

  /* If one value is a string and the other is a blob, the string is less.
  ** If both are strings, compare using the collating functions.
  */
  if( combined_flags&MEM_Str ){
    if( (f1 & MEM_Str)==0 ){
      return 1;
    }
    if( (f2 & MEM_Str)==0 ){
      return -1;
    }

    assert( pMem1->enc==pMem2->enc );
    assert( pMem1->enc==SQLITE_UTF8 || 
            pMem1->enc==SQLITE_UTF16LE || pMem1->enc==SQLITE_UTF16BE );

    /* The collation sequence must be defined at this point, even if
    ** the user deletes the collation sequence after the vdbe program is
    ** compiled (this was not always the case).
    */
    assert( !pColl || pColl->xCmp );

    if( pColl ){
      if( pMem1->enc==pColl->enc ){
        /* The strings are already in the correct encoding.  Call the
        ** comparison function directly */
        return pColl->xCmp(pColl->pUser,pMem1->n,pMem1->z,pMem2->n,pMem2->z);
      }else{
        u8 origEnc = pMem1->enc;
        const void *v1, *v2;
        int n1, n2;
        /* Convert the strings into the encoding that the comparison
        ** function expects */
        v1 = sqlite3ValueText((sqlite3_value*)pMem1, pColl->enc);
        n1 = v1==0 ? 0 : pMem1->n;
        assert( n1==sqlite3ValueBytes((sqlite3_value*)pMem1, pColl->enc) );
        v2 = sqlite3ValueText((sqlite3_value*)pMem2, pColl->enc);
        n2 = v2==0 ? 0 : pMem2->n;
        assert( n2==sqlite3ValueBytes((sqlite3_value*)pMem2, pColl->enc) );
        /* Do the comparison */
        rc = pColl->xCmp(pColl->pUser, n1, v1, n2, v2);
        /* Convert the strings back into the database encoding */
        sqlite3ValueText((sqlite3_value*)pMem1, origEnc);
        sqlite3ValueText((sqlite3_value*)pMem2, origEnc);
        return rc;
      }
    }
    /* If a NULL pointer was passed as the collate function, fall through
    ** to the blob case and use memcmp().  */
  }
 
  /* Both values must be blobs.  Compare using memcmp().  */
  rc = memcmp(pMem1->z, pMem2->z, (pMem1->n>pMem2->n)?pMem2->n:pMem1->n);
  if( rc==0 ){
    rc = pMem1->n - pMem2->n;
  }
  return rc;
}

/*
** Move data out of a btree key or data field and into a Mem structure.
** The data or key is taken from the entry that pCur is currently pointing
** to.  offset and amt determine what portion of the data or key to retrieve.
** key is true to get the key or false to get data.  The result is written
** into the pMem element.
**
** The pMem structure is assumed to be uninitialized.  Any prior content
** is overwritten without being freed.
**
** If this routine fails for any reason (malloc returns NULL or unable
** to read from the disk) then the pMem is left in an inconsistent state.
*/
int sqlite3VdbeMemFromBtree(
  BtCursor *pCur,   /* Cursor pointing at record to retrieve. */
  int offset,       /* Offset from the start of data to return bytes from. */
  int amt,          /* Number of bytes to return. */
  int key,          /* If true, retrieve from the btree key, not data. */
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  char *zData;      /* Data from the btree layer */
  int available;    /* Number of bytes available on the local btree page */

  if( key ){
    zData = (char *)sqlite3BtreeKeyFetch(pCur, &available);
  }else{
    zData = (char *)sqlite3BtreeDataFetch(pCur, &available);
  }

  pMem->n = amt;
  if( offset+amt<=available ){
    pMem->z = &zData[offset];
    pMem->flags = MEM_Blob|MEM_Ephem;
  }else{
    int rc;
    if( amt>NBFS-2 ){
      zData = (char *)sqliteMallocRaw(amt+2);
      if( !zData ){
        return SQLITE_NOMEM;
      }
      pMem->flags = MEM_Blob|MEM_Dyn|MEM_Term;
      pMem->xDel = 0;
    }else{
      zData = &(pMem->zShort[0]);
      pMem->flags = MEM_Blob|MEM_Short|MEM_Term;
    }
    pMem->z = zData;
    pMem->enc = 0;
    pMem->type = SQLITE_BLOB;

    if( key ){
      rc = sqlite3BtreeKey(pCur, offset, amt, zData);
    }else{
      rc = sqlite3BtreeData(pCur, offset, amt, zData);
    }
    zData[amt] = 0;
    zData[amt+1] = 0;
    if( rc!=SQLITE_OK ){
      if( amt>NBFS-2 ){
        assert( zData!=pMem->zShort );
        assert( pMem->flags & MEM_Dyn );
        sqliteFree(zData);
      } else {
        assert( zData==pMem->zShort );
        assert( pMem->flags & MEM_Short );
      }
      return rc;
    }
  }

  return SQLITE_OK;
}

#ifndef NDEBUG
/*
** Perform various checks on the memory cell pMem. An assert() will
** fail if pMem is internally inconsistent.
*/
void sqlite3VdbeMemSanity(Mem *pMem){
  int flags = pMem->flags;
  assert( flags!=0 );  /* Must define some type */
  if( pMem->flags & (MEM_Str|MEM_Blob) ){
    int x = pMem->flags & (MEM_Static|MEM_Dyn|MEM_Ephem|MEM_Short);
    assert( x!=0 );            /* Strings must define a string subtype */
    assert( (x & (x-1))==0 );  /* Only one string subtype can be defined */
    assert( pMem->z!=0 );      /* Strings must have a value */
    /* Mem.z points to Mem.zShort iff the subtype is MEM_Short */
    assert( (pMem->flags & MEM_Short)==0 || pMem->z==pMem->zShort );
    assert( (pMem->flags & MEM_Short)!=0 || pMem->z!=pMem->zShort );
    /* No destructor unless there is MEM_Dyn */
    assert( pMem->xDel==0 || (pMem->flags & MEM_Dyn)!=0 );

    if( (flags & MEM_Str) ){
      assert( pMem->enc==SQLITE_UTF8 || 
              pMem->enc==SQLITE_UTF16BE ||
              pMem->enc==SQLITE_UTF16LE 
      );
      /* If the string is UTF-8 encoded and nul terminated, then pMem->n
      ** must be the length of the string.  (Later:)  If the database file
      ** has been corrupted, '\000' characters might have been inserted
      ** into the middle of the string.  In that case, the strlen() might
      ** be less.
      */
      if( pMem->enc==SQLITE_UTF8 && (flags & MEM_Term) ){ 
        assert( strlen(pMem->z)<=pMem->n );
        assert( pMem->z[pMem->n]==0 );
      }
    }
  }else{
    /* Cannot define a string subtype for non-string objects */
    assert( (pMem->flags & (MEM_Static|MEM_Dyn|MEM_Ephem|MEM_Short))==0 );
    assert( pMem->xDel==0 );
  }
  /* MEM_Null excludes all other types */
  assert( (pMem->flags&(MEM_Str|MEM_Int|MEM_Real|MEM_Blob))==0
          || (pMem->flags&MEM_Null)==0 );
  /* If the MEM is both real and integer, the values are equal */
  assert( (pMem->flags & (MEM_Int|MEM_Real))!=(MEM_Int|MEM_Real) 
          || pMem->r==pMem->i );
}
#endif

/* This function is only available internally, it is not part of the
** external API. It works in a similar way to sqlite3_value_text(),
** except the data returned is in the encoding specified by the second
** parameter, which must be one of SQLITE_UTF16BE, SQLITE_UTF16LE or
** SQLITE_UTF8.
**
** (2006-02-16:)  The enc value can be or-ed with SQLITE_UTF16_ALIGNED.
** If that is the case, then the result must be aligned on an even byte
** boundary.
*/
const void *sqlite3ValueText(sqlite3_value* pVal, u8 enc){
  if( !pVal ) return 0;
  assert( (enc&3)==(enc&~SQLITE_UTF16_ALIGNED) );

  if( pVal->flags&MEM_Null ){
    return 0;
  }
  assert( (MEM_Blob>>3) == MEM_Str );
  pVal->flags |= (pVal->flags & MEM_Blob)>>3;
  if( pVal->flags&MEM_Str ){
    sqlite3VdbeChangeEncoding(pVal, enc & ~SQLITE_UTF16_ALIGNED);
    if( (enc & SQLITE_UTF16_ALIGNED)!=0 && 1==(1&(int)pVal->z) ){
      assert( (pVal->flags & (MEM_Ephem|MEM_Static))!=0 );
      if( sqlite3VdbeMemMakeWriteable(pVal)!=SQLITE_OK ){
        return 0;
      }
    }
    sqlite3VdbeMemNulTerminate(pVal);
  }else{
    assert( (pVal->flags&MEM_Blob)==0 );
    sqlite3VdbeMemStringify(pVal, enc);
    assert( 0==(1&(int)pVal->z) );
  }
  assert(pVal->enc==(enc & ~SQLITE_UTF16_ALIGNED) || sqlite3MallocFailed() );
  if( pVal->enc==(enc & ~SQLITE_UTF16_ALIGNED) ){
    return pVal->z;
  }else{
    return 0;
  }
}

/*
** Create a new sqlite3_value object.
*/
sqlite3_value* sqlite3ValueNew(void){
  Mem *p = sqliteMalloc(sizeof(*p));
  if( p ){
    p->flags = MEM_Null;
    p->type = SQLITE_NULL;
  }
  return p;
}

/*
** Create a new sqlite3_value object, containing the value of pExpr.
**
** This only works for very simple expressions that consist of one constant
** token (i.e. "5", "5.1", "NULL", "'a string'"). If the expression can
** be converted directly into a value, then the value is allocated and
** a pointer written to *ppVal. The caller is responsible for deallocating
** the value by passing it to sqlite3ValueFree() later on. If the expression
** cannot be converted to a value, then *ppVal is set to NULL.
*/
int sqlite3ValueFromExpr(
  Expr *pExpr, 
  u8 enc, 
  u8 affinity,
  sqlite3_value **ppVal
){
  int op;
  char *zVal = 0;
  sqlite3_value *pVal = 0;

  if( !pExpr ){
    *ppVal = 0;
    return SQLITE_OK;
  }
  op = pExpr->op;

  if( op==TK_STRING || op==TK_FLOAT || op==TK_INTEGER ){
    zVal = sqliteStrNDup((char*)pExpr->token.z, pExpr->token.n);
    pVal = sqlite3ValueNew();
    if( !zVal || !pVal ) goto no_mem;
    sqlite3Dequote(zVal);
    sqlite3ValueSetStr(pVal, -1, zVal, SQLITE_UTF8, sqlite3FreeX);
    if( (op==TK_INTEGER || op==TK_FLOAT ) && affinity==SQLITE_AFF_NONE ){
      sqlite3ValueApplyAffinity(pVal, SQLITE_AFF_NUMERIC, enc);
    }else{
      sqlite3ValueApplyAffinity(pVal, affinity, enc);
    }
  }else if( op==TK_UMINUS ) {
    if( SQLITE_OK==sqlite3ValueFromExpr(pExpr->pLeft, enc, affinity, &pVal) ){
      pVal->i = -1 * pVal->i;
      pVal->r = -1.0 * pVal->r;
    }
  }
#ifndef SQLITE_OMIT_BLOB_LITERAL
  else if( op==TK_BLOB ){
    int nVal;
    pVal = sqlite3ValueNew();
    zVal = sqliteStrNDup((char*)pExpr->token.z+1, pExpr->token.n-1);
    if( !zVal || !pVal ) goto no_mem;
    sqlite3Dequote(zVal);
    nVal = strlen(zVal)/2;
    sqlite3VdbeMemSetStr(pVal, sqlite3HexToBlob(zVal), nVal, 0, sqlite3FreeX);
    sqliteFree(zVal);
  }
#endif

  *ppVal = pVal;
  return SQLITE_OK;

no_mem:
  sqliteFree(zVal);
  sqlite3ValueFree(pVal);
  *ppVal = 0;
  return SQLITE_NOMEM;
}

/*
** Change the string value of an sqlite3_value object
*/
void sqlite3ValueSetStr(
  sqlite3_value *v, 
  int n, 
  const void *z, 
  u8 enc,
  void (*xDel)(void*)
){
  if( v ) sqlite3VdbeMemSetStr((Mem *)v, z, n, enc, xDel);
}

/*
** Free an sqlite3_value object
*/
void sqlite3ValueFree(sqlite3_value *v){
  if( !v ) return;
  sqlite3ValueSetStr(v, 0, 0, SQLITE_UTF8, SQLITE_STATIC);
  sqliteFree(v);
}

/*
** Return the number of bytes in the sqlite3_value object assuming
** that it uses the encoding "enc"
*/
int sqlite3ValueBytes(sqlite3_value *pVal, u8 enc){
  Mem *p = (Mem*)pVal;
  if( (p->flags & MEM_Blob)!=0 || sqlite3ValueText(pVal, enc) ){
    return p->n;
  }
  return 0;
}