DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

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/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** The code in this file implements execution method of the 
** Virtual Database Engine (VDBE).  A separate file ("vdbeaux.c")
** handles housekeeping details such as creating and deleting
** VDBE instances.  This file is solely interested in executing
** the VDBE program.
**
** In the external interface, an "sqlite3_stmt*" is an opaque pointer
** to a VDBE.
**
** The SQL parser generates a program which is then executed by
** the VDBE to do the work of the SQL statement.  VDBE programs are 
** similar in form to assembly language.  The program consists of
** a linear sequence of operations.  Each operation has an opcode 
** and 3 operands.  Operands P1 and P2 are integers.  Operand P3 
** is a null-terminated string.   The P2 operand must be non-negative.
** Opcodes will typically ignore one or more operands.  Many opcodes
** ignore all three operands.
**
** Computation results are stored on a stack.  Each entry on the
** stack is either an integer, a null-terminated string, a floating point
** number, or the SQL "NULL" value.  An inplicit conversion from one
** type to the other occurs as necessary.
** 
** Most of the code in this file is taken up by the sqlite3VdbeExec()
** function which does the work of interpreting a VDBE program.
** But other routines are also provided to help in building up
** a program instruction by instruction.
**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.548 2006/03/22 22:10:08 drh Exp $
*/
#include "sqliteInt.h"
#include "os.h"
#include <ctype.h>
#include "vdbeInt.h"

/*
** The following global variable is incremented every time a cursor
** moves, either by the OP_MoveXX, 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.
*/
int sqlite3_search_count = 0;

/*
** When this global variable is positive, it gets decremented once before
** each instruction in the VDBE.  When reaches zero, the SQLITE_Interrupt
** of the db.flags field is set in order to simulate and interrupt.
**
** This facility is used for testing purposes only.  It does not function
** in an ordinary build.
*/
int sqlite3_interrupt_count = 0;

/*
** The next global variable is incremented each type the OP_Sort opcode
** is executed.  The test procedures use this information to make sure that
** sorting is occurring or not occuring at appropriate times.   This variable
** has no function other than to help verify the correct operation of the
** library.
*/
int sqlite3_sort_count = 0;

/*
** Release the memory associated with the given stack level.  This
** leaves the Mem.flags field in an inconsistent state.
*/
#define Release(P) if((P)->flags&MEM_Dyn){ sqlite3VdbeMemRelease(P); }

/*
** Convert the given stack entity into a string if it isn't one
** already. Return non-zero if a malloc() fails.
*/
#define Stringify(P, enc) \
   if(((P)->flags&(MEM_Str|MEM_Blob))==0 && sqlite3VdbeMemStringify(P,enc)) \
     { goto no_mem; }

/*
** Convert the given stack entity into a string that has been obtained
** from sqliteMalloc().  This is different from Stringify() above in that
** Stringify() will use the NBFS bytes of static string space if the string
** will fit but this routine always mallocs for space.
** Return non-zero if we run out of memory.
*/
#define Dynamicify(P,enc) sqlite3VdbeMemDynamicify(P)

/*
** The header of a record consists of a sequence variable-length integers.
** These integers are almost always small and are encoded as a single byte.
** The following macro takes advantage this fact to provide a fast decode
** of the integers in a record header.  It is faster for the common case
** where the integer is a single byte.  It is a little slower when the
** integer is two or more bytes.  But overall it is faster.
**
** The following expressions are equivalent:
**
**     x = sqlite3GetVarint32( A, &B );
**
**     x = GetVarint( A, B );
**
*/
#define GetVarint(A,B)  ((B = *(A))<=0x7f ? 1 : sqlite3GetVarint32(A, &B))

/*
** An ephemeral string value (signified by the MEM_Ephem flag) contains
** a pointer to a dynamically allocated string where some other entity
** is responsible for deallocating that string.  Because the stack entry
** does not control the string, it might be deleted without the stack
** entry knowing it.
**
** This routine converts an ephemeral string into a dynamically allocated
** string that the stack entry itself controls.  In other words, it
** converts an MEM_Ephem string into an MEM_Dyn string.
*/
#define Deephemeralize(P) \
   if( ((P)->flags&MEM_Ephem)!=0 \
       && sqlite3VdbeMemMakeWriteable(P) ){ goto no_mem;}

/*
** Argument pMem points at a memory cell that will be passed to a
** user-defined function or returned to the user as the result of a query.
** The second argument, 'db_enc' is the text encoding used by the vdbe for
** stack variables.  This routine sets the pMem->enc and pMem->type
** variables used by the sqlite3_value_*() routines.
*/
#define storeTypeInfo(A,B) _storeTypeInfo(A)
static void _storeTypeInfo(Mem *pMem){
  int flags = pMem->flags;
  if( flags & MEM_Null ){
    pMem->type = SQLITE_NULL;
  }
  else if( flags & MEM_Int ){
    pMem->type = SQLITE_INTEGER;
  }
  else if( flags & MEM_Real ){
    pMem->type = SQLITE_FLOAT;
  }
  else if( flags & MEM_Str ){
    pMem->type = SQLITE_TEXT;
  }else{
    pMem->type = SQLITE_BLOB;
  }
}

/*
** Pop the stack N times.
*/
static void popStack(Mem **ppTos, int N){
  Mem *pTos = *ppTos;
  while( N>0 ){
    N--;
    Release(pTos);
    pTos--;
  }
  *ppTos = pTos;
}

/*
** Allocate cursor number iCur.  Return a pointer to it.  Return NULL
** if we run out of memory.
*/
static Cursor *allocateCursor(Vdbe *p, int iCur, int iDb){
  Cursor *pCx;
  assert( iCur<p->nCursor );
  if( p->apCsr[iCur] ){
    sqlite3VdbeFreeCursor(p->apCsr[iCur]);
  }
  p->apCsr[iCur] = pCx = sqliteMalloc( sizeof(Cursor) );
  if( pCx ){
    pCx->iDb = iDb;
  }
  return pCx;
}

/*
** Try to convert a value into a numeric representation if we can
** do so without loss of information.  In other words, if the string
** looks like a number, convert it into a number.  If it does not
** look like a number, leave it alone.
*/
static void applyNumericAffinity(Mem *pRec){
  if( (pRec->flags & (MEM_Real|MEM_Int))==0 ){
    int realnum;
    sqlite3VdbeMemNulTerminate(pRec);
    if( (pRec->flags&MEM_Str)
         && sqlite3IsNumber(pRec->z, &realnum, pRec->enc) ){
      i64 value;
      sqlite3VdbeChangeEncoding(pRec, SQLITE_UTF8);
      if( !realnum && sqlite3atoi64(pRec->z, &value) ){
        sqlite3VdbeMemRelease(pRec);
        pRec->i = value;
        pRec->flags = MEM_Int;
      }else{
        sqlite3VdbeMemRealify(pRec);
      }
    }
  }
}

/*
** Processing is determine by the affinity parameter:
**
** SQLITE_AFF_INTEGER:
** SQLITE_AFF_REAL:
** SQLITE_AFF_NUMERIC:
**    Try to convert pRec to an integer representation or a 
**    floating-point representation if an integer representation
**    is not possible.  Note that the integer representation is
**    always preferred, even if the affinity is REAL, because
**    an integer representation is more space efficient on disk.
**
** SQLITE_AFF_TEXT:
**    Convert pRec to a text representation.
**
** SQLITE_AFF_NONE:
**    No-op.  pRec is unchanged.
*/
static void applyAffinity(Mem *pRec, char affinity, u8 enc){
  if( affinity==SQLITE_AFF_TEXT ){
    /* Only attempt the conversion to TEXT if there is an integer or real
    ** representation (blob and NULL do not get converted) but no string
    ** representation.
    */
    if( 0==(pRec->flags&MEM_Str) && (pRec->flags&(MEM_Real|MEM_Int)) ){
      sqlite3VdbeMemStringify(pRec, enc);
    }
    pRec->flags &= ~(MEM_Real|MEM_Int);
  }else if( affinity!=SQLITE_AFF_NONE ){
    assert( affinity==SQLITE_AFF_INTEGER || affinity==SQLITE_AFF_REAL
             || affinity==SQLITE_AFF_NUMERIC );
    applyNumericAffinity(pRec);
    if( pRec->flags & MEM_Real ){
      sqlite3VdbeIntegerAffinity(pRec);
    }
  }
}

/*
** Try to convert the type of a function argument or a result column
** into a numeric representation.  Use either INTEGER or REAL whichever
** is appropriate.  But only do the conversion if it is possible without
** loss of information and return the revised type of the argument.
**
** This is an EXPERIMENTAL api and is subject to change or removal.
*/
int sqlite3_value_numeric_type(sqlite3_value *pVal){
  Mem *pMem = (Mem*)pVal;
  applyNumericAffinity(pMem);
  storeTypeInfo(pMem, 0);
  return pMem->type;
}

/*
** Exported version of applyAffinity(). This one works on sqlite3_value*, 
** not the internal Mem* type.
*/
void sqlite3ValueApplyAffinity(sqlite3_value *pVal, u8 affinity, u8 enc){
  applyAffinity((Mem *)pVal, affinity, enc);
}

#ifdef SQLITE_DEBUG
/*
** Write a nice string representation of the contents of cell pMem
** into buffer zBuf, length nBuf.
*/
void sqlite3VdbeMemPrettyPrint(Mem *pMem, char *zBuf){
  char *zCsr = zBuf;
  int f = pMem->flags;

  static const char *const encnames[] = {"(X)", "(8)", "(16LE)", "(16BE)"};

  if( f&MEM_Blob ){
    int i;
    char c;
    if( f & MEM_Dyn ){
      c = 'z';
      assert( (f & (MEM_Static|MEM_Ephem))==0 );
    }else if( f & MEM_Static ){
      c = 't';
      assert( (f & (MEM_Dyn|MEM_Ephem))==0 );
    }else if( f & MEM_Ephem ){
      c = 'e';
      assert( (f & (MEM_Static|MEM_Dyn))==0 );
    }else{
      c = 's';
    }

    zCsr += sprintf(zCsr, "%c", c);
    zCsr += sprintf(zCsr, "%d[", pMem->n);
    for(i=0; i<16 && i<pMem->n; i++){
      zCsr += sprintf(zCsr, "%02X ", ((int)pMem->z[i] & 0xFF));
    }
    for(i=0; i<16 && i<pMem->n; i++){
      char z = pMem->z[i];
      if( z<32 || z>126 ) *zCsr++ = '.';
      else *zCsr++ = z;
    }

    zCsr += sprintf(zCsr, "]");
    *zCsr = '\0';
  }else if( f & MEM_Str ){
    int j, k;
    zBuf[0] = ' ';
    if( f & MEM_Dyn ){
      zBuf[1] = 'z';
      assert( (f & (MEM_Static|MEM_Ephem))==0 );
    }else if( f & MEM_Static ){
      zBuf[1] = 't';
      assert( (f & (MEM_Dyn|MEM_Ephem))==0 );
    }else if( f & MEM_Ephem ){
      zBuf[1] = 'e';
      assert( (f & (MEM_Static|MEM_Dyn))==0 );
    }else{
      zBuf[1] = 's';
    }
    k = 2;
    k += sprintf(&zBuf[k], "%d", pMem->n);
    zBuf[k++] = '[';
    for(j=0; j<15 && j<pMem->n; j++){
      u8 c = pMem->z[j];
      if( c>=0x20 && c<0x7f ){
        zBuf[k++] = c;
      }else{
        zBuf[k++] = '.';
      }
    }
    zBuf[k++] = ']';
    k += sprintf(&zBuf[k], encnames[pMem->enc]);
    zBuf[k++] = 0;
  }
}
#endif


#ifdef VDBE_PROFILE
/*
** The following routine only works on pentium-class processors.
** It uses the RDTSC opcode to read the cycle count value out of the
** processor and returns that value.  This can be used for high-res
** profiling.
*/
__inline__ unsigned long long int hwtime(void){
  unsigned long long int x;
  __asm__("rdtsc\n\t"
          "mov %%edx, %%ecx\n\t"
          :"=A" (x));
  return x;
}
#endif

/*
** The CHECK_FOR_INTERRUPT macro defined here looks to see if the
** sqlite3_interrupt() routine has been called.  If it has been, then
** processing of the VDBE program is interrupted.
**
** This macro added to every instruction that does a jump in order to
** implement a loop.  This test used to be on every single instruction,
** but that meant we more testing that we needed.  By only testing the
** flag on jump instructions, we get a (small) speed improvement.
*/
#define CHECK_FOR_INTERRUPT \
   if( db->flags & SQLITE_Interrupt ) goto abort_due_to_interrupt;


/*
** Execute as much of a VDBE program as we can then return.
**
** sqlite3VdbeMakeReady() must be called before this routine in order to
** close the program with a final OP_Halt and to set up the callbacks
** and the error message pointer.
**
** Whenever a row or result data is available, this routine will either
** invoke the result callback (if there is one) or return with
** SQLITE_ROW.
**
** If an attempt is made to open a locked database, then this routine
** will either invoke the busy callback (if there is one) or it will
** return SQLITE_BUSY.
**
** If an error occurs, an error message is written to memory obtained
** from sqliteMalloc() and p->zErrMsg is made to point to that memory.
** The error code is stored in p->rc and this routine returns SQLITE_ERROR.
**
** If the callback ever returns non-zero, then the program exits
** immediately.  There will be no error message but the p->rc field is
** set to SQLITE_ABORT and this routine will return SQLITE_ERROR.
**
** A memory allocation error causes p->rc to be set to SQLITE_NOMEM and this
** routine to return SQLITE_ERROR.
**
** Other fatal errors return SQLITE_ERROR.
**
** After this routine has finished, sqlite3VdbeFinalize() should be
** used to clean up the mess that was left behind.
*/
int sqlite3VdbeExec(
  Vdbe *p                    /* The VDBE */
){
  int pc;                    /* The program counter */
  Op *pOp;                   /* Current operation */
  int rc = SQLITE_OK;        /* Value to return */
  sqlite3 *db = p->db;       /* The database */
  u8 encoding = ENC(db);     /* The database encoding */
  Mem *pTos;                 /* Top entry in the operand stack */
#ifdef VDBE_PROFILE
  unsigned long long start;  /* CPU clock count at start of opcode */
  int origPc;                /* Program counter at start of opcode */
#endif
#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
  int nProgressOps = 0;      /* Opcodes executed since progress callback. */
#endif
#ifndef NDEBUG
  Mem *pStackLimit;
#endif

  if( p->magic!=VDBE_MAGIC_RUN ) return SQLITE_MISUSE;
  assert( db->magic==SQLITE_MAGIC_BUSY );
  pTos = p->pTos;
  if( p->rc==SQLITE_NOMEM ){
    /* This happens if a malloc() inside a call to sqlite3_column_text() or
    ** sqlite3_column_text16() failed.  */
    goto no_mem;
  }
  assert( p->rc==SQLITE_OK || p->rc==SQLITE_BUSY );
  p->rc = SQLITE_OK;
  assert( p->explain==0 );
  if( p->popStack ){
    popStack(&pTos, p->popStack);
    p->popStack = 0;
  }
  p->resOnStack = 0;
  db->busyHandler.nBusy = 0;
  CHECK_FOR_INTERRUPT;
  for(pc=p->pc; rc==SQLITE_OK; pc++){
    assert( pc>=0 && pc<p->nOp );
    assert( pTos<=&p->aStack[pc] );
    if( sqlite3MallocFailed() ) goto no_mem;
#ifdef VDBE_PROFILE
    origPc = pc;
    start = hwtime();
#endif
    pOp = &p->aOp[pc];

    /* Only allow tracing if SQLITE_DEBUG is defined.
    */
#ifdef SQLITE_DEBUG
    if( p->trace ){
      if( pc==0 ){
        printf("VDBE Execution Trace:\n");
        sqlite3VdbePrintSql(p);
      }
      sqlite3VdbePrintOp(p->trace, pc, pOp);
    }
    if( p->trace==0 && pc==0 && sqlite3OsFileExists("vdbe_sqltrace") ){
      sqlite3VdbePrintSql(p);
    }
#endif
      

    /* Check to see if we need to simulate an interrupt.  This only happens
    ** if we have a special test build.
    */
#ifdef SQLITE_TEST
    if( sqlite3_interrupt_count>0 ){
      sqlite3_interrupt_count--;
      if( sqlite3_interrupt_count==0 ){
        sqlite3_interrupt(db);
      }
    }
#endif

#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
    /* Call the progress callback if it is configured and the required number
    ** of VDBE ops have been executed (either since this invocation of
    ** sqlite3VdbeExec() or since last time the progress callback was called).
    ** If the progress callback returns non-zero, exit the virtual machine with
    ** a return code SQLITE_ABORT.
    */
    if( db->xProgress ){
      if( db->nProgressOps==nProgressOps ){
        if( db->xProgress(db->pProgressArg)!=0 ){
          rc = SQLITE_ABORT;
          continue; /* skip to the next iteration of the for loop */
        }
        nProgressOps = 0;
      }
      nProgressOps++;
    }
#endif

#ifndef NDEBUG
    /* This is to check that the return value of static function
    ** opcodeNoPush() (see vdbeaux.c) returns values that match the
    ** implementation of the virtual machine in this file. If
    ** opcodeNoPush() returns non-zero, then the stack is guarenteed
    ** not to grow when the opcode is executed. If it returns zero, then
    ** the stack may grow by at most 1.
    **
    ** The global wrapper function sqlite3VdbeOpcodeUsesStack() is not 
    ** available if NDEBUG is defined at build time.
    */ 
    pStackLimit = pTos;
    if( !sqlite3VdbeOpcodeNoPush(pOp->opcode) ){
      pStackLimit++;
    }
#endif

    switch( pOp->opcode ){

/*****************************************************************************
** What follows is a massive switch statement where each case implements a
** separate instruction in the virtual machine.  If we follow the usual
** indentation conventions, each case should be indented by 6 spaces.  But
** that is a lot of wasted space on the left margin.  So the code within
** the switch statement will break with convention and be flush-left. Another
** big comment (similar to this one) will mark the point in the code where
** we transition back to normal indentation.
**
** The formatting of each case is important.  The makefile for SQLite
** generates two C files "opcodes.h" and "opcodes.c" by scanning this
** file looking for lines that begin with "case OP_".  The opcodes.h files
** will be filled with #defines that give unique integer values to each
** opcode and the opcodes.c file is filled with an array of strings where
** each string is the symbolic name for the corresponding opcode.  If the
** case statement is followed by a comment of the form "/# same as ... #/"
** that comment is used to determine the particular value of the opcode.
**
** If a comment on the same line as the "case OP_" construction contains
** the word "no-push", then the opcode is guarenteed not to grow the 
** vdbe stack when it is executed. See function opcode() in
** vdbeaux.c for details.
**
** Documentation about VDBE opcodes is generated by scanning this file
** for lines of that contain "Opcode:".  That line and all subsequent
** comment lines are used in the generation of the opcode.html documentation
** file.
**
** SUMMARY:
**
**     Formatting is important to scripts that scan this file.
**     Do not deviate from the formatting style currently in use.
**
*****************************************************************************/

/* Opcode:  Goto * P2 *
**
** An unconditional jump to address P2.
** The next instruction executed will be 
** the one at index P2 from the beginning of
** the program.
*/
case OP_Goto: {             /* no-push */
  CHECK_FOR_INTERRUPT;
  pc = pOp->p2 - 1;
  break;
}

/* Opcode:  Gosub * P2 *
**
** Push the current address plus 1 onto the return address stack
** and then jump to address P2.
**
** The return address stack is of limited depth.  If too many
** OP_Gosub operations occur without intervening OP_Returns, then
** the return address stack will fill up and processing will abort
** with a fatal error.
*/
case OP_Gosub: {            /* no-push */
  assert( p->returnDepth<sizeof(p->returnStack)/sizeof(p->returnStack[0]) );
  p->returnStack[p->returnDepth++] = pc+1;
  pc = pOp->p2 - 1;
  break;
}

/* Opcode:  Return * * *
**
** Jump immediately to the next instruction after the last unreturned
** OP_Gosub.  If an OP_Return has occurred for all OP_Gosubs, then
** processing aborts with a fatal error.
*/
case OP_Return: {           /* no-push */
  assert( p->returnDepth>0 );
  p->returnDepth--;
  pc = p->returnStack[p->returnDepth] - 1;
  break;
}

/* Opcode:  Halt P1 P2 P3
**
** Exit immediately.  All open cursors, Fifos, etc are closed
** automatically.
**
** P1 is the result code returned by sqlite3_exec(), sqlite3_reset(),
** or sqlite3_finalize().  For a normal halt, this should be SQLITE_OK (0).
** For errors, it can be some other value.  If P1!=0 then P2 will determine
** whether or not to rollback the current transaction.  Do not rollback
** if P2==OE_Fail. Do the rollback if P2==OE_Rollback.  If P2==OE_Abort,
** then back out all changes that have occurred during this execution of the
** VDBE, but do not rollback the transaction. 
**
** If P3 is not null then it is an error message string.
**
** There is an implied "Halt 0 0 0" instruction inserted at the very end of
** every program.  So a jump past the last instruction of the program
** is the same as executing Halt.
*/
case OP_Halt: {            /* no-push */
  p->pTos = pTos;
  p->rc = pOp->p1;
  p->pc = pc;
  p->errorAction = pOp->p2;
  if( pOp->p3 ){
    sqlite3SetString(&p->zErrMsg, pOp->p3, (char*)0);
  }
  rc = sqlite3VdbeHalt(p);
  assert( rc==SQLITE_BUSY || rc==SQLITE_OK );
  if( rc==SQLITE_BUSY ){
    p->rc = SQLITE_BUSY;
    return SQLITE_BUSY;
  }
  return p->rc ? SQLITE_ERROR : SQLITE_DONE;
}

/* Opcode: Integer P1 * *
**
** The 32-bit integer value P1 is pushed onto the stack.
*/
case OP_Integer: {
  pTos++;
  pTos->flags = MEM_Int;
  pTos->i = pOp->p1;
  break;
}

/* Opcode: Int64 * * P3
**
** P3 is a string representation of an integer.  Convert that integer
** to a 64-bit value and push it onto the stack.
*/
case OP_Int64: {
  pTos++;
  assert( pOp->p3!=0 );
  pTos->flags = MEM_Str|MEM_Static|MEM_Term;
  pTos->z = pOp->p3;
  pTos->n = strlen(pTos->z);
  pTos->enc = SQLITE_UTF8;
  pTos->i = sqlite3VdbeIntValue(pTos);
  pTos->flags |= MEM_Int;
  break;
}

/* Opcode: Real * * P3
**
** The string value P3 is converted to a real and pushed on to the stack.
*/
case OP_Real: {            /* same as TK_FLOAT, */
  pTos++;
  pTos->flags = MEM_Str|MEM_Static|MEM_Term;
  pTos->z = pOp->p3;
  pTos->n = strlen(pTos->z);
  pTos->enc = SQLITE_UTF8;
  pTos->r = sqlite3VdbeRealValue(pTos);
  pTos->flags |= MEM_Real;
  sqlite3VdbeChangeEncoding(pTos, encoding);
  break;
}

/* Opcode: String8 * * P3
**
** P3 points to a nul terminated UTF-8 string. This opcode is transformed 
** into an OP_String before it is executed for the first time.
*/
case OP_String8: {         /* same as TK_STRING */
  assert( pOp->p3!=0 );
  pOp->opcode = OP_String;
  pOp->p1 = strlen(pOp->p3);

#ifndef SQLITE_OMIT_UTF16
  if( encoding!=SQLITE_UTF8 ){
    pTos++;
    sqlite3VdbeMemSetStr(pTos, pOp->p3, -1, SQLITE_UTF8, SQLITE_STATIC);
    if( SQLITE_OK!=sqlite3VdbeChangeEncoding(pTos, encoding) ) goto no_mem;
    if( SQLITE_OK!=sqlite3VdbeMemDynamicify(pTos) ) goto no_mem;
    pTos->flags &= ~(MEM_Dyn);
    pTos->flags |= MEM_Static;
    if( pOp->p3type==P3_DYNAMIC ){
      sqliteFree(pOp->p3);
    }
    pOp->p3type = P3_DYNAMIC;
    pOp->p3 = pTos->z;
    pOp->p1 = pTos->n;
    break;
  }
#endif
  /* Otherwise fall through to the next case, OP_String */
}
  
/* Opcode: String P1 * P3
**
** The string value P3 of length P1 (bytes) is pushed onto the stack.
*/
case OP_String: {
  pTos++;
  assert( pOp->p3!=0 );
  pTos->flags = MEM_Str|MEM_Static|MEM_Term;
  pTos->z = pOp->p3;
  pTos->n = pOp->p1;
  pTos->enc = encoding;
  break;
}

/* Opcode: Null * * *
**
** Push a NULL onto the stack.
*/
case OP_Null: {
  pTos++;
  pTos->flags = MEM_Null;
  pTos->n = 0;
  break;
}


#ifndef SQLITE_OMIT_BLOB_LITERAL
/* Opcode: HexBlob * * P3
**
** P3 is an UTF-8 SQL hex encoding of a blob. The blob is pushed onto the
** vdbe stack.
**
** The first time this instruction executes, in transforms itself into a
** 'Blob' opcode with a binary blob as P3.
*/
case OP_HexBlob: {            /* same as TK_BLOB */
  pOp->opcode = OP_Blob;
  pOp->p1 = strlen(pOp->p3)/2;
  if( pOp->p1 ){
    char *zBlob = sqlite3HexToBlob(pOp->p3);
    if( !zBlob ) goto no_mem;
    if( pOp->p3type==P3_DYNAMIC ){
      sqliteFree(pOp->p3);
    }
    pOp->p3 = zBlob;
    pOp->p3type = P3_DYNAMIC;
  }else{
    if( pOp->p3type==P3_DYNAMIC ){
      sqliteFree(pOp->p3);
    }
    pOp->p3type = P3_STATIC;
    pOp->p3 = "";
  }

  /* Fall through to the next case, OP_Blob. */
}

/* Opcode: Blob P1 * P3
**
** P3 points to a blob of data P1 bytes long. Push this
** value onto the stack. This instruction is not coded directly
** by the compiler. Instead, the compiler layer specifies
** an OP_HexBlob opcode, with the hex string representation of
** the blob as P3. This opcode is transformed to an OP_Blob
** the first time it is executed.
*/
case OP_Blob: {
  pTos++;
  sqlite3VdbeMemSetStr(pTos, pOp->p3, pOp->p1, 0, 0);
  break;
}
#endif /* SQLITE_OMIT_BLOB_LITERAL */

/* Opcode: Variable P1 * *
**
** Push the value of variable P1 onto the stack.  A variable is
** an unknown in the original SQL string as handed to sqlite3_compile().
** Any occurance of the '?' character in the original SQL is considered
** a variable.  Variables in the SQL string are number from left to
** right beginning with 1.  The values of variables are set using the
** sqlite3_bind() API.
*/
case OP_Variable: {
  int j = pOp->p1 - 1;
  assert( j>=0 && j<p->nVar );

  pTos++;
  sqlite3VdbeMemShallowCopy(pTos, &p->aVar[j], MEM_Static);
  break;
}

/* Opcode: Pop P1 * *
**
** P1 elements are popped off of the top of stack and discarded.
*/
case OP_Pop: {            /* no-push */
  assert( pOp->p1>=0 );
  popStack(&pTos, pOp->p1);
  assert( pTos>=&p->aStack[-1] );
  break;
}

/* Opcode: Dup P1 P2 *
**
** A copy of the P1-th element of the stack 
** is made and pushed onto the top of the stack.
** The top of the stack is element 0.  So the
** instruction "Dup 0 0 0" will make a copy of the
** top of the stack.
**
** If the content of the P1-th element is a dynamically
** allocated string, then a new copy of that string
** is made if P2==0.  If P2!=0, then just a pointer
** to the string is copied.
**
** Also see the Pull instruction.
*/
case OP_Dup: {
  Mem *pFrom = &pTos[-pOp->p1];
  assert( pFrom<=pTos && pFrom>=p->aStack );
  pTos++;
  sqlite3VdbeMemShallowCopy(pTos, pFrom, MEM_Ephem);
  if( pOp->p2 ){
    Deephemeralize(pTos);
  }
  break;
}

/* Opcode: Pull P1 * *
**
** The P1-th element is removed from its current location on 
** the stack and pushed back on top of the stack.  The
** top of the stack is element 0, so "Pull 0 0 0" is
** a no-op.  "Pull 1 0 0" swaps the top two elements of
** the stack.
**
** See also the Dup instruction.
*/
case OP_Pull: {            /* no-push */
  Mem *pFrom = &pTos[-pOp->p1];
  int i;
  Mem ts;

  ts = *pFrom;
  Deephemeralize(pTos);
  for(i=0; i<pOp->p1; i++, pFrom++){
    Deephemeralize(&pFrom[1]);
    assert( (pFrom->flags & MEM_Ephem)==0 );
    *pFrom = pFrom[1];
    if( pFrom->flags & MEM_Short ){
      assert( pFrom->flags & (MEM_Str|MEM_Blob) );
      assert( pFrom->z==pFrom[1].zShort );
      pFrom->z = pFrom->zShort;
    }
  }
  *pTos = ts;
  if( pTos->flags & MEM_Short ){
    assert( pTos->flags & (MEM_Str|MEM_Blob) );
    assert( pTos->z==pTos[-pOp->p1].zShort );
    pTos->z = pTos->zShort;
  }
  break;
}

/* Opcode: Push P1 * *
**
** Overwrite the value of the P1-th element down on the
** stack (P1==0 is the top of the stack) with the value
** of the top of the stack.  Then pop the top of the stack.
*/
case OP_Push: {            /* no-push */
  Mem *pTo = &pTos[-pOp->p1];

  assert( pTo>=p->aStack );
  sqlite3VdbeMemMove(pTo, pTos);
  pTos--;
  break;
}

/* Opcode: Callback P1 * *
**
** The top P1 values on the stack represent a single result row from
** a query.  This opcode causes the sqlite3_step() call to terminate
** with an SQLITE_ROW return code and it sets up the sqlite3_stmt
** structure to provide access to the top P1 values as the result
** row.  When the sqlite3_step() function is run again, the top P1
** values will be automatically popped from the stack before the next
** instruction executes.
*/
case OP_Callback: {            /* no-push */
  Mem *pMem;
  Mem *pFirstColumn;
  assert( p->nResColumn==pOp->p1 );

  /* Data in the pager might be moved or changed out from under us
  ** in between the return from this sqlite3_step() call and the
  ** next call to sqlite3_step().  So deephermeralize everything on 
  ** the stack.  Note that ephemeral data is never stored in memory 
  ** cells so we do not have to worry about them.
  */
  pFirstColumn = &pTos[0-pOp->p1];
  for(pMem = p->aStack; pMem<pFirstColumn; pMem++){
    Deephemeralize(pMem);
  }

  /* Invalidate all ephemeral cursor row caches */
  p->cacheCtr = (p->cacheCtr + 2)|1;

  /* Make sure the results of the current row are \000 terminated
  ** and have an assigned type.  The results are deephemeralized as
  ** as side effect.
  */
  for(; pMem<=pTos; pMem++ ){
    sqlite3VdbeMemNulTerminate(pMem);
    storeTypeInfo(pMem, encoding);
  }

  /* Set up the statement structure so that it will pop the current
  ** results from the stack when the statement returns.
  */
  p->resOnStack = 1;
  p->nCallback++;
  p->popStack = pOp->p1;
  p->pc = pc + 1;
  p->pTos = pTos;
  return SQLITE_ROW;
}

/* Opcode: Concat P1 P2 *
**
** Look at the first P1+2 elements of the stack.  Append them all 
** together with the lowest element first.  The original P1+2 elements
** are popped from the stack if P2==0 and retained if P2==1.  If
** any element of the stack is NULL, then the result is NULL.
**
** When P1==1, this routine makes a copy of the top stack element
** into memory obtained from sqliteMalloc().
*/
case OP_Concat: {           /* same as TK_CONCAT */
  char *zNew;
  int nByte;
  int nField;
  int i, j;
  Mem *pTerm;

  /* Loop through the stack elements to see how long the result will be. */
  nField = pOp->p1 + 2;
  pTerm = &pTos[1-nField];
  nByte = 0;
  for(i=0; i<nField; i++, pTerm++){
    assert( pOp->p2==0 || (pTerm->flags&MEM_Str) );
    if( pTerm->flags&MEM_Null ){
      nByte = -1;
      break;
    }
    Stringify(pTerm, encoding);
    nByte += pTerm->n;
  }

  if( nByte<0 ){
    /* If nByte is less than zero, then there is a NULL value on the stack.
    ** In this case just pop the values off the stack (if required) and
    ** push on a NULL.
    */
    if( pOp->p2==0 ){
      popStack(&pTos, nField);
    }
    pTos++;
    pTos->flags = MEM_Null;
  }else{
    /* Otherwise malloc() space for the result and concatenate all the
    ** stack values.
    */
    zNew = sqliteMallocRaw( nByte+2 );
    if( zNew==0 ) goto no_mem;
    j = 0;
    pTerm = &pTos[1-nField];
    for(i=j=0; i<nField; i++, pTerm++){
      int n = pTerm->n;
      assert( pTerm->flags & (MEM_Str|MEM_Blob) );
      memcpy(&zNew[j], pTerm->z, n);
      j += n;
    }
    zNew[j] = 0;
    zNew[j+1] = 0;
    assert( j==nByte );

    if( pOp->p2==0 ){
      popStack(&pTos, nField);
    }
    pTos++;
    pTos->n = j;
    pTos->flags = MEM_Str|MEM_Dyn|MEM_Term;
    pTos->xDel = 0;
    pTos->enc = encoding;
    pTos->z = zNew;
  }
  break;
}

/* Opcode: Add * * *
**
** Pop the top two elements from the stack, add them together,
** and push the result back onto the stack.  If either element
** is a string then it is converted to a double using the atof()
** function before the addition.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: Multiply * * *
**
** Pop the top two elements from the stack, multiply them together,
** and push the result back onto the stack.  If either element
** is a string then it is converted to a double using the atof()
** function before the multiplication.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: Subtract * * *
**
** Pop the top two elements from the stack, subtract the
** first (what was on top of the stack) from the second (the
** next on stack)
** and push the result back onto the stack.  If either element
** is a string then it is converted to a double using the atof()
** function before the subtraction.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: Divide * * *
**
** Pop the top two elements from the stack, divide the
** first (what was on top of the stack) from the second (the
** next on stack)
** and push the result back onto the stack.  If either element
** is a string then it is converted to a double using the atof()
** function before the division.  Division by zero returns NULL.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: Remainder * * *
**
** Pop the top two elements from the stack, divide the
** first (what was on top of the stack) from the second (the
** next on stack)
** and push the remainder after division onto the stack.  If either element
** is a string then it is converted to a double using the atof()
** function before the division.  Division by zero returns NULL.
** If either operand is NULL, the result is NULL.
*/
case OP_Add:                   /* same as TK_PLUS, no-push */
case OP_Subtract:              /* same as TK_MINUS, no-push */
case OP_Multiply:              /* same as TK_STAR, no-push */
case OP_Divide:                /* same as TK_SLASH, no-push */
case OP_Remainder: {           /* same as TK_REM, no-push */
  Mem *pNos = &pTos[-1];
  int flags;
  assert( pNos>=p->aStack );
  flags = pTos->flags | pNos->flags;
  if( (flags & MEM_Null)!=0 ){
    Release(pTos);
    pTos--;
    Release(pTos);
    pTos->flags = MEM_Null;
  }else if( (pTos->flags & pNos->flags & MEM_Int)==MEM_Int ){
    i64 a, b;
    a = pTos->i;
    b = pNos->i;
    switch( pOp->opcode ){
      case OP_Add:         b += a;       break;
      case OP_Subtract:    b -= a;       break;
      case OP_Multiply:    b *= a;       break;
      case OP_Divide: {
        if( a==0 ) goto divide_by_zero;
        b /= a;
        break;
      }
      default: {
        if( a==0 ) goto divide_by_zero;
        b %= a;
        break;
      }
    }
    Release(pTos);
    pTos--;
    Release(pTos);
    pTos->i = b;
    pTos->flags = MEM_Int;
  }else{
    double a, b;
    a = sqlite3VdbeRealValue(pTos);
    b = sqlite3VdbeRealValue(pNos);
    switch( pOp->opcode ){
      case OP_Add:         b += a;       break;
      case OP_Subtract:    b -= a;       break;
      case OP_Multiply:    b *= a;       break;
      case OP_Divide: {
        if( a==0.0 ) goto divide_by_zero;
        b /= a;
        break;
      }
      default: {
        int ia = (int)a;
        int ib = (int)b;
        if( ia==0.0 ) goto divide_by_zero;
        b = ib % ia;
        break;
      }
    }
    Release(pTos);
    pTos--;
    Release(pTos);
    pTos->r = b;
    pTos->flags = MEM_Real;
    if( (flags & MEM_Real)==0 ){
      sqlite3VdbeIntegerAffinity(pTos);
    }
  }
  break;

divide_by_zero:
  Release(pTos);
  pTos--;
  Release(pTos);
  pTos->flags = MEM_Null;
  break;
}

/* Opcode: CollSeq * * P3
**
** P3 is a pointer to a CollSeq struct. If the next call to a user function
** or aggregate calls sqlite3GetFuncCollSeq(), this collation sequence will
** be returned. This is used by the built-in min(), max() and nullif()
** functions.
**
** The interface used by the implementation of the aforementioned functions
** to retrieve the collation sequence set by this opcode is not available
** publicly, only to user functions defined in func.c.
*/
case OP_CollSeq: {             /* no-push */
  assert( pOp->p3type==P3_COLLSEQ );
  break;
}

/* Opcode: Function P1 P2 P3
**
** Invoke a user function (P3 is a pointer to a Function structure that
** defines the function) with P2 arguments taken from the stack.  Pop all
** arguments from the stack and push back the result.
**
** P1 is a 32-bit bitmask indicating whether or not each argument to the 
** function was determined to be constant at compile time. If the first
** argument was constant then bit 0 of P1 is set. This is used to determine
** whether meta data associated with a user function argument using the
** sqlite3_set_auxdata() API may be safely retained until the next
** invocation of this opcode.
**
** See also: AggStep and AggFinal
*/
case OP_Function: {
  int i;
  Mem *pArg;
  sqlite3_context ctx;
  sqlite3_value **apVal;
  int n = pOp->p2;

  apVal = p->apArg;
  assert( apVal || n==0 );

  pArg = &pTos[1-n];
  for(i=0; i<n; i++, pArg++){
    apVal[i] = pArg;
    storeTypeInfo(pArg, encoding);
  }

  assert( pOp->p3type==P3_FUNCDEF || pOp->p3type==P3_VDBEFUNC );
  if( pOp->p3type==P3_FUNCDEF ){
    ctx.pFunc = (FuncDef*)pOp->p3;
    ctx.pVdbeFunc = 0;
  }else{
    ctx.pVdbeFunc = (VdbeFunc*)pOp->p3;
    ctx.pFunc = ctx.pVdbeFunc->pFunc;
  }

  ctx.s.flags = MEM_Null;
  ctx.s.z = 0;
  ctx.s.xDel = 0;
  ctx.isError = 0;
  if( ctx.pFunc->needCollSeq ){
    assert( pOp>p->aOp );
    assert( pOp[-1].p3type==P3_COLLSEQ );
    assert( pOp[-1].opcode==OP_CollSeq );
    ctx.pColl = (CollSeq *)pOp[-1].p3;
  }
  if( sqlite3SafetyOff(db) ) goto abort_due_to_misuse;
  (*ctx.pFunc->xFunc)(&ctx, n, apVal);
  if( sqlite3SafetyOn(db) ) goto abort_due_to_misuse;
  if( sqlite3MallocFailed() ) goto no_mem;
  popStack(&pTos, n);

  /* If any auxilary data functions have been called by this user function,
  ** immediately call the destructor for any non-static values.
  */
  if( ctx.pVdbeFunc ){
    sqlite3VdbeDeleteAuxData(ctx.pVdbeFunc, pOp->p1);
    pOp->p3 = (char *)ctx.pVdbeFunc;
    pOp->p3type = P3_VDBEFUNC;
  }

  /* If the function returned an error, throw an exception */
  if( ctx.isError ){
    sqlite3SetString(&p->zErrMsg, sqlite3_value_text(&ctx.s), (char*)0);
    rc = SQLITE_ERROR;
  }

  /* Copy the result of the function to the top of the stack */
  sqlite3VdbeChangeEncoding(&ctx.s, encoding);
  pTos++;
  pTos->flags = 0;
  sqlite3VdbeMemMove(pTos, &ctx.s);
  break;
}

/* Opcode: BitAnd * * *
**
** Pop the top two elements from the stack.  Convert both elements
** to integers.  Push back onto the stack the bit-wise AND of the
** two elements.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: BitOr * * *
**
** Pop the top two elements from the stack.  Convert both elements
** to integers.  Push back onto the stack the bit-wise OR of the
** two elements.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: ShiftLeft * * *
**
** Pop the top two elements from the stack.  Convert both elements
** to integers.  Push back onto the stack the second element shifted
** left by N bits where N is the top element on the stack.
** If either operand is NULL, the result is NULL.
*/
/* Opcode: ShiftRight * * *
**
** Pop the top two elements from the stack.  Convert both elements
** to integers.  Push back onto the stack the second element shifted
** right by N bits where N is the top element on the stack.
** If either operand is NULL, the result is NULL.
*/
case OP_BitAnd:                 /* same as TK_BITAND, no-push */
case OP_BitOr:                  /* same as TK_BITOR, no-push */
case OP_ShiftLeft:              /* same as TK_LSHIFT, no-push */
case OP_ShiftRight: {           /* same as TK_RSHIFT, no-push */
  Mem *pNos = &pTos[-1];
  i64 a, b;

  assert( pNos>=p->aStack );
  if( (pTos->flags | pNos->flags) & MEM_Null ){
    popStack(&pTos, 2);
    pTos++;
    pTos->flags = MEM_Null;
    break;
  }
  a = sqlite3VdbeIntValue(pNos);
  b = sqlite3VdbeIntValue(pTos);
  switch( pOp->opcode ){
    case OP_BitAnd:      a &= b;     break;
    case OP_BitOr:       a |= b;     break;
    case OP_ShiftLeft:   a <<= b;    break;
    case OP_ShiftRight:  a >>= b;    break;
    default:   /* CANT HAPPEN */     break;
  }
  Release(pTos);
  pTos--;
  Release(pTos);
  pTos->i = a;
  pTos->flags = MEM_Int;
  break;
}

/* Opcode: AddImm  P1 * *
** 
** Add the value P1 to whatever is on top of the stack.  The result
** is always an integer.
**
** To force the top of the stack to be an integer, just add 0.
*/
case OP_AddImm: {            /* no-push */
  assert( pTos>=p->aStack );
  sqlite3VdbeMemIntegerify(pTos);
  pTos->i += pOp->p1;
  break;
}

/* Opcode: ForceInt P1 P2 *
**
** Convert the top of the stack into an integer.  If the current top of
** the stack is not numeric (meaning that is is a NULL or a string that
** does not look like an integer or floating point number) then pop the
** stack and jump to P2.  If the top of the stack is numeric then
** convert it into the least integer that is greater than or equal to its
** current value if P1==0, or to the least integer that is strictly
** greater than its current value if P1==1.
*/
case OP_ForceInt: {            /* no-push */
  i64 v;
  assert( pTos>=p->aStack );
  applyAffinity(pTos, SQLITE_AFF_NUMERIC, encoding);
  if( (pTos->flags & (MEM_Int|MEM_Real))==0 ){
    Release(pTos);
    pTos--;
    pc = pOp->p2 - 1;
    break;
  }
  if( pTos->flags & MEM_Int ){
    v = pTos->i + (pOp->p1!=0);
  }else{
    /* FIX ME:  should this not be assert( pTos->flags & MEM_Real ) ??? */
    sqlite3VdbeMemRealify(pTos);
    v = (int)pTos->r;
    if( pTos->r>(double)v ) v++;
    if( pOp->p1 && pTos->r==(double)v ) v++;
  }
  Release(pTos);
  pTos->i = v;
  pTos->flags = MEM_Int;
  break;
}

/* Opcode: MustBeInt P1 P2 *
** 
** Force the top of the stack to be an integer.  If the top of the
** stack is not an integer and cannot be converted into an integer
** with out data loss, then jump immediately to P2, or if P2==0
** raise an SQLITE_MISMATCH exception.
**
** If the top of the stack is not an integer and P2 is not zero and
** P1 is 1, then the stack is popped.  In all other cases, the depth
** of the stack is unchanged.
*/
case OP_MustBeInt: {            /* no-push */
  assert( pTos>=p->aStack );
  applyAffinity(pTos, SQLITE_AFF_NUMERIC, encoding);
  if( (pTos->flags & MEM_Int)==0 ){
    if( pOp->p2==0 ){
      rc = SQLITE_MISMATCH;
      goto abort_due_to_error;
    }else{
      if( pOp->p1 ) popStack(&pTos, 1);
      pc = pOp->p2 - 1;
    }
  }else{
    Release(pTos);
    pTos->flags = MEM_Int;
  }
  break;
}

/* Opcode: RealAffinity * * *
**
** If the top of the stack is an integer, convert it to a real value.
**
** This opcode is used when extracting information from a column that
** has REAL affinity.  Such column values may still be stored as
** integers, for space efficiency, but after extraction we want them
** to have only a real value.
*/
case OP_RealAffinity: {                  /* no-push */
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Int ){
    sqlite3VdbeMemRealify(pTos);
  }
  break;
}

#ifndef SQLITE_OMIT_CAST
/* Opcode: ToText * * *
**
** Force the value on the top of the stack to be text.
** If the value is numeric, convert it to a string using the
** equivalent of printf().  Blob values are unchanged and
** are afterwards simply interpreted as text.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToText: {                  /* same as TK_TO_TEXT, no-push */
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Null ) break;
  assert( MEM_Str==(MEM_Blob>>3) );
  pTos->flags |= (pTos->flags&MEM_Blob)>>3;
  applyAffinity(pTos, SQLITE_AFF_TEXT, encoding);
  assert( pTos->flags & MEM_Str );
  pTos->flags &= ~(MEM_Int|MEM_Real|MEM_Blob);
  break;
}

/* Opcode: ToBlob * * *
**
** Force the value on the top of the stack to be a BLOB.
** If the value is numeric, convert it to a string first.
** Strings are simply reinterpreted as blobs with no change
** to the underlying data.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToBlob: {                  /* same as TK_TO_BLOB, no-push */
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Null ) break;
  if( (pTos->flags & MEM_Blob)==0 ){
    applyAffinity(pTos, SQLITE_AFF_TEXT, encoding);
    assert( pTos->flags & MEM_Str );
    pTos->flags |= MEM_Blob;
  }
  pTos->flags &= ~(MEM_Int|MEM_Real|MEM_Str);
  break;
}

/* Opcode: ToNumeric * * *
**
** Force the value on the top of the stack to be numeric (either an
** integer or a floating-point number.)
** If the value is text or blob, try to convert it to an using the
** equivalent of atoi() or atof() and store 0 if no such conversion 
** is possible.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToNumeric: {                  /* same as TK_TO_NUMERIC, no-push */
  assert( pTos>=p->aStack );
  if( (pTos->flags & MEM_Null)==0 ){
    sqlite3VdbeMemNumerify(pTos);
  }
  break;
}
#endif /* SQLITE_OMIT_CAST */

/* Opcode: ToInt * * *
**
** Force the value on the top of the stack to be an integer.  If
** The value is currently a real number, drop its fractional part.
** If the value is text or blob, try to convert it to an integer using the
** equivalent of atoi() and store 0 if no such conversion is possible.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToInt: {                  /* same as TK_TO_INT, no-push */
  assert( pTos>=p->aStack );
  if( (pTos->flags & MEM_Null)==0 ){
    sqlite3VdbeMemIntegerify(pTos);
  }
  break;
}

#ifndef SQLITE_OMIT_CAST
/* Opcode: ToReal * * *
**
** Force the value on the top of the stack to be a floating point number.
** If The value is currently an integer, convert it.
** If the value is text or blob, try to convert it to an integer using the
** equivalent of atoi() and store 0 if no such conversion is possible.
**
** A NULL value is not changed by this routine.  It remains NULL.
*/
case OP_ToReal: {                  /* same as TK_TO_REAL, no-push */
  assert( pTos>=p->aStack );
  if( (pTos->flags & MEM_Null)==0 ){
    sqlite3VdbeMemRealify(pTos);
  }
  break;
}
#endif /* SQLITE_OMIT_CAST */

/* Opcode: Eq P1 P2 P3
**
** Pop the top two elements from the stack.  If they are equal, then
** jump to instruction P2.  Otherwise, continue to the next instruction.
**
** If the 0x100 bit of P1 is true and either operand is NULL then take the
** jump.  If the 0x100 bit of P1 is clear then fall thru if either operand
** is NULL.
**
** If the 0x200 bit of P1 is set and either operand is NULL then
** both operands are converted to integers prior to comparison.
** NULL operands are converted to zero and non-NULL operands are
** converted to 1.  Thus, for example, with 0x200 set,  NULL==NULL is true
** whereas it would normally be NULL.  Similarly,  NULL==123 is false when
** 0x200 is set but is NULL when the 0x200 bit of P1 is clear.
**
** The least significant byte of P1 (mask 0xff) must be an affinity character -
** SQLITE_AFF_TEXT, SQLITE_AFF_INTEGER, and so forth. An attempt is made 
** to coerce both values
** according to the affinity before the comparison is made. If the byte is
** 0x00, then numeric affinity is used.
**
** Once any conversions have taken place, and neither value is NULL, 
** the values are compared. If both values are blobs, or both are text,
** then memcmp() is used to determine the results of the comparison. If
** both values are numeric, then a numeric comparison is used. If the
** two values are of different types, then they are inequal.
**
** If P2 is zero, do not jump.  Instead, push an integer 1 onto the
** stack if the jump would have been taken, or a 0 if not.  Push a
** NULL if either operand was NULL.
**
** If P3 is not NULL it is a pointer to a collating sequence (a CollSeq
** structure) that defines how to compare text.
*/
/* Opcode: Ne P1 P2 P3
**
** This works just like the Eq opcode except that the jump is taken if
** the operands from the stack are not equal.  See the Eq opcode for
** additional information.
*/
/* Opcode: Lt P1 P2 P3
**
** This works just like the Eq opcode except that the jump is taken if
** the 2nd element down on the stack is less than the top of the stack.
** See the Eq opcode for additional information.
*/
/* Opcode: Le P1 P2 P3
**
** This works just like the Eq opcode except that the jump is taken if
** the 2nd element down on the stack is less than or equal to the
** top of the stack.  See the Eq opcode for additional information.
*/
/* Opcode: Gt P1 P2 P3
**
** This works just like the Eq opcode except that the jump is taken if
** the 2nd element down on the stack is greater than the top of the stack.
** See the Eq opcode for additional information.
*/
/* Opcode: Ge P1 P2 P3
**
** This works just like the Eq opcode except that the jump is taken if
** the 2nd element down on the stack is greater than or equal to the
** top of the stack.  See the Eq opcode for additional information.
*/
case OP_Eq:               /* same as TK_EQ, no-push */
case OP_Ne:               /* same as TK_NE, no-push */
case OP_Lt:               /* same as TK_LT, no-push */
case OP_Le:               /* same as TK_LE, no-push */
case OP_Gt:               /* same as TK_GT, no-push */
case OP_Ge: {             /* same as TK_GE, no-push */
  Mem *pNos;
  int flags;
  int res;
  char affinity;

  pNos = &pTos[-1];
  flags = pTos->flags|pNos->flags;

  /* If either value is a NULL P2 is not zero, take the jump if the least
  ** significant byte of P1 is true. If P2 is zero, then push a NULL onto
  ** the stack.
  */
  if( flags&MEM_Null ){
    if( (pOp->p1 & 0x200)!=0 ){
      /* The 0x200 bit of P1 means, roughly "do not treat NULL as the
      ** magic SQL value it normally is - treat it as if it were another
      ** integer".
      **
      ** With 0x200 set, if either operand is NULL then both operands
      ** are converted to integers prior to being passed down into the
      ** normal comparison logic below.  NULL operands are converted to
      ** zero and non-NULL operands are converted to 1.  Thus, for example,
      ** with 0x200 set,  NULL==NULL is true whereas it would normally
      ** be NULL.  Similarly,  NULL!=123 is true.
      */
      sqlite3VdbeMemSetInt64(pTos, (pTos->flags & MEM_Null)==0);
      sqlite3VdbeMemSetInt64(pNos, (pNos->flags & MEM_Null)==0);
    }else{
      /* If the 0x200 bit of P1 is clear and either operand is NULL then
      ** the result is always NULL.  The jump is taken if the 0x100 bit
      ** of P1 is set.
      */
      popStack(&pTos, 2);
      if( pOp->p2 ){
        if( pOp->p1 & 0x100 ){
          pc = pOp->p2-1;
        }
      }else{
        pTos++;
        pTos->flags = MEM_Null;
      }
      break;
    }
  }

  affinity = pOp->p1 & 0xFF;
  if( affinity ){
    applyAffinity(pNos, affinity, encoding);
    applyAffinity(pTos, affinity, encoding);
  }

  assert( pOp->p3type==P3_COLLSEQ || pOp->p3==0 );
  res = sqlite3MemCompare(pNos, pTos, (CollSeq*)pOp->p3);
  switch( pOp->opcode ){
    case OP_Eq:    res = res==0;     break;
    case OP_Ne:    res = res!=0;     break;
    case OP_Lt:    res = res<0;      break;
    case OP_Le:    res = res<=0;     break;
    case OP_Gt:    res = res>0;      break;
    default:       res = res>=0;     break;
  }

  popStack(&pTos, 2);
  if( pOp->p2 ){
    if( res ){
      pc = pOp->p2-1;
    }
  }else{
    pTos++;
    pTos->flags = MEM_Int;
    pTos->i = res;
  }
  break;
}

/* Opcode: And * * *
**
** Pop two values off the stack.  Take the logical AND of the
** two values and push the resulting boolean value back onto the
** stack. 
*/
/* Opcode: Or * * *
**
** Pop two values off the stack.  Take the logical OR of the
** two values and push the resulting boolean value back onto the
** stack. 
*/
case OP_And:              /* same as TK_AND, no-push */
case OP_Or: {             /* same as TK_OR, no-push */
  Mem *pNos = &pTos[-1];
  int v1, v2;    /* 0==TRUE, 1==FALSE, 2==UNKNOWN or NULL */

  assert( pNos>=p->aStack );
  if( pTos->flags & MEM_Null ){
    v1 = 2;
  }else{
    sqlite3VdbeMemIntegerify(pTos);
    v1 = pTos->i==0;
  }
  if( pNos->flags & MEM_Null ){
    v2 = 2;
  }else{
    sqlite3VdbeMemIntegerify(pNos);
    v2 = pNos->i==0;
  }
  if( pOp->opcode==OP_And ){
    static const unsigned char and_logic[] = { 0, 1, 2, 1, 1, 1, 2, 1, 2 };
    v1 = and_logic[v1*3+v2];
  }else{
    static const unsigned char or_logic[] = { 0, 0, 0, 0, 1, 2, 0, 2, 2 };
    v1 = or_logic[v1*3+v2];
  }
  popStack(&pTos, 2);
  pTos++;
  if( v1==2 ){
    pTos->flags = MEM_Null;
  }else{
    pTos->i = v1==0;
    pTos->flags = MEM_Int;
  }
  break;
}

/* Opcode: Negative * * *
**
** Treat the top of the stack as a numeric quantity.  Replace it
** with its additive inverse.  If the top of the stack is NULL
** its value is unchanged.
*/
/* Opcode: AbsValue * * *
**
** Treat the top of the stack as a numeric quantity.  Replace it
** with its absolute value. If the top of the stack is NULL
** its value is unchanged.
*/
case OP_Negative:              /* same as TK_UMINUS, no-push */
case OP_AbsValue: {
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Real ){
    neg_abs_real_case:
    Release(pTos);
    if( pOp->opcode==OP_Negative || pTos->r<0.0 ){
      pTos->r = -pTos->r;
    }
    pTos->flags = MEM_Real;
  }else if( pTos->flags & MEM_Int ){
    Release(pTos);
    if( pOp->opcode==OP_Negative || pTos->i<0 ){
      pTos->i = -pTos->i;
    }
    pTos->flags = MEM_Int;
  }else if( pTos->flags & MEM_Null ){
    /* Do nothing */
  }else{
    sqlite3VdbeMemNumerify(pTos);
    goto neg_abs_real_case;
  }
  break;
}

/* Opcode: Not * * *
**
** Interpret the top of the stack as a boolean value.  Replace it
** with its complement.  If the top of the stack is NULL its value
** is unchanged.
*/
case OP_Not: {                /* same as TK_NOT, no-push */
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Null ) break;  /* Do nothing to NULLs */
  sqlite3VdbeMemIntegerify(pTos);
  assert( (pTos->flags & MEM_Dyn)==0 );
  pTos->i = !pTos->i;
  pTos->flags = MEM_Int;
  break;
}

/* Opcode: BitNot * * *
**
** Interpret the top of the stack as an value.  Replace it
** with its ones-complement.  If the top of the stack is NULL its
** value is unchanged.
*/
case OP_BitNot: {             /* same as TK_BITNOT, no-push */
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Null ) break;  /* Do nothing to NULLs */
  sqlite3VdbeMemIntegerify(pTos);
  assert( (pTos->flags & MEM_Dyn)==0 );
  pTos->i = ~pTos->i;
  pTos->flags = MEM_Int;
  break;
}

/* Opcode: Noop * * *
**
** Do nothing.  This instruction is often useful as a jump
** destination.
*/
/*
** The magic Explain opcode are only inserted when explain==2 (which
** is to say when the EXPLAIN QUERY PLAN syntax is used.)
** This opcode records information from the optimizer.  It is the
** the same as a no-op.  This opcodesnever appears in a real VM program.
*/
case OP_Explain:
case OP_Noop: {            /* no-push */
  break;
}

/* Opcode: If P1 P2 *
**
** Pop a single boolean from the stack.  If the boolean popped is
** true, then jump to p2.  Otherwise continue to the next instruction.
** An integer is false if zero and true otherwise.  A string is
** false if it has zero length and true otherwise.
**
** If the value popped of the stack is NULL, then take the jump if P1
** is true and fall through if P1 is false.
*/
/* Opcode: IfNot P1 P2 *
**
** Pop a single boolean from the stack.  If the boolean popped is
** false, then jump to p2.  Otherwise continue to the next instruction.
** An integer is false if zero and true otherwise.  A string is
** false if it has zero length and true otherwise.
**
** If the value popped of the stack is NULL, then take the jump if P1
** is true and fall through if P1 is false.
*/
case OP_If:                 /* no-push */
case OP_IfNot: {            /* no-push */
  int c;
  assert( pTos>=p->aStack );
  if( pTos->flags & MEM_Null ){
    c = pOp->p1;
  }else{
#ifdef SQLITE_OMIT_FLOATING_POINT
    c = sqlite3VdbeIntValue(pTos);
#else
    c = sqlite3VdbeRealValue(pTos)!=0.0;
#endif
    if( pOp->opcode==OP_IfNot ) c = !c;
  }
  Release(pTos);
  pTos--;
  if( c ) pc = pOp->p2-1;
  break;
}

/* Opcode: IsNull P1 P2 *
**
** If any of the top abs(P1) values on the stack are NULL, then jump
** to P2.  Pop the stack P1 times if P1>0.   If P1<0 leave the stack
** unchanged.
*/
case OP_IsNull: {            /* same as TK_ISNULL, no-push */
  int i, cnt;
  Mem *pTerm;
  cnt = pOp->p1;
  if( cnt<0 ) cnt = -cnt;
  pTerm = &pTos[1-cnt];
  assert( pTerm>=p->aStack );
  for(i=0; i<cnt; i++, pTerm++){
    if( pTerm->flags & MEM_Null ){
      pc = pOp->p2-1;
      break;
    }
  }
  if( pOp->p1>0 ) popStack(&pTos, cnt);
  break;
}

/* Opcode: NotNull P1 P2 *
**
** Jump to P2 if the top P1 values on the stack are all not NULL.  Pop the
** stack if P1 times if P1 is greater than zero.  If P1 is less than
** zero then leave the stack unchanged.
*/
case OP_NotNull: {            /* same as TK_NOTNULL, no-push */
  int i, cnt;
  cnt = pOp->p1;
  if( cnt<0 ) cnt = -cnt;
  assert( &pTos[1-cnt] >= p->aStack );
  for(i=0; i<cnt && (pTos[1+i-cnt].flags & MEM_Null)==0; i++){}
  if( i>=cnt ) pc = pOp->p2-1;
  if( pOp->p1>0 ) popStack(&pTos, cnt);
  break;
}

/* Opcode: SetNumColumns P1 P2 *
**
** Before the OP_Column opcode can be executed on a cursor, this
** opcode must be called to set the number of fields in the table.
**
** This opcode sets the number of columns for cursor P1 to P2.
**
** If OP_KeyAsData is to be applied to cursor P1, it must be executed
** before this op-code.
*/
case OP_SetNumColumns: {       /* no-push */
  Cursor *pC;
  assert( (pOp->p1)<p->nCursor );
  assert( p->apCsr[pOp->p1]!=0 );
  pC = p->apCsr[pOp->p1];
  pC->nField = pOp->p2;
  break;
}

/* Opcode: Column P1 P2 P3
**
** Interpret the data that cursor P1 points to as a structure built using
** the MakeRecord instruction.  (See the MakeRecord opcode for additional
** information about the format of the data.) Push onto the stack the value
** of the P2-th column contained in the data. If there are less that (P2+1) 
** values in the record, push a NULL onto the stack.
**
** If the KeyAsData opcode has previously executed on this cursor, then the
** field might be extracted from the key rather than the data.
**
** If the column contains fewer than P2 fields, then push a NULL.  Or
** if P3 is of type P3_MEM, then push the P3 value.  The P3 value will
** be default value for a column that has been added using the ALTER TABLE
** ADD COLUMN command.  If P3 is an ordinary string, just push a NULL.
** When P3 is a string it is really just a comment describing the value
** to be pushed, not a default value.
*/
case OP_Column: {
  u32 payloadSize;   /* Number of bytes in the record */
  int p1 = pOp->p1;  /* P1 value of the opcode */
  int p2 = pOp->p2;  /* column number to retrieve */
  Cursor *pC = 0;    /* The VDBE cursor */
  char *zRec;        /* Pointer to complete record-data */
  BtCursor *pCrsr;   /* The BTree cursor */
  u32 *aType;        /* aType[i] holds the numeric type of the i-th column */
  u32 *aOffset;      /* aOffset[i] is offset to start of data for i-th column */
  u32 nField;        /* number of fields in the record */
  int len;           /* The length of the serialized data for the column */
  int i;             /* Loop counter */
  char *zData;       /* Part of the record being decoded */
  Mem sMem;          /* For storing the record being decoded */

  sMem.flags = 0;
  assert( p1<p->nCursor );
  pTos++;
  pTos->flags = MEM_Null;

  /* This block sets the variable payloadSize to be the total number of
  ** bytes in the record.
  **
  ** zRec is set to be the complete text of the record if it is available.
  ** The complete record text is always available for pseudo-tables
  ** If the record is stored in a cursor, the complete record text
  ** might be available in the  pC->aRow cache.  Or it might not be.
  ** If the data is unavailable,  zRec is set to NULL.
  **
  ** We also compute the number of columns in the record.  For cursors,
  ** the number of columns is stored in the Cursor.nField element.  For
  ** records on the stack, the next entry down on the stack is an integer
  ** which is the number of records.
  */
  pC = p->apCsr[p1];
  assert( pC!=0 );
  if( pC->pCursor!=0 ){
    /* The record is stored in a B-Tree */
    rc = sqlite3VdbeCursorMoveto(pC);
    if( rc ) goto abort_due_to_error;
    zRec = 0;
    pCrsr = pC->pCursor;
    if( pC->nullRow ){
      payloadSize = 0;
    }else if( pC->cacheStatus==p->cacheCtr ){
      payloadSize = pC->payloadSize;
      zRec = (char*)pC->aRow;
    }else if( pC->isIndex ){
      i64 payloadSize64;
      sqlite3BtreeKeySize(pCrsr, &payloadSize64);
      payloadSize = payloadSize64;
    }else{
      sqlite3BtreeDataSize(pCrsr, &payloadSize);
    }
    nField = pC->nField;
  }else if( pC->pseudoTable ){
    /* The record is the sole entry of a pseudo-table */
    payloadSize = pC->nData;
    zRec = pC->pData;
    pC->cacheStatus = CACHE_STALE;
    assert( payloadSize==0 || zRec!=0 );
    nField = pC->nField;
    pCrsr = 0;
  }else{
    zRec = 0;
    payloadSize = 0;
    pCrsr = 0;
    nField = 0;
  }

  /* If payloadSize is 0, then just push a NULL onto the stack. */
  if( payloadSize==0 ){
    assert( pTos->flags==MEM_Null );
    break;
  }

  assert( p2<nField );

  /* Read and parse the table header.  Store the results of the parse
  ** into the record header cache fields of the cursor.
  */
  if( pC && pC->cacheStatus==p->cacheCtr ){
    aType = pC->aType;
    aOffset = pC->aOffset;
  }else{
    u8 *zIdx;        /* Index into header */
    u8 *zEndHdr;     /* Pointer to first byte after the header */
    u32 offset;      /* Offset into the data */
    int szHdrSz;     /* Size of the header size field at start of record */
    int avail;       /* Number of bytes of available data */

    aType = pC->aType;
    if( aType==0 ){
      pC->aType = aType = sqliteMallocRaw( 2*nField*sizeof(aType) );
    }
    if( aType==0 ){
      goto no_mem;
    }
    pC->aOffset = aOffset = &aType[nField];
    pC->payloadSize = payloadSize;
    pC->cacheStatus = p->cacheCtr;

    /* Figure out how many bytes are in the header */
    if( zRec ){
      zData = zRec;
    }else{
      if( pC->isIndex ){
        zData = (char*)sqlite3BtreeKeyFetch(pCrsr, &avail);
      }else{
        zData = (char*)sqlite3BtreeDataFetch(pCrsr, &avail);
      }
      /* If KeyFetch()/DataFetch() managed to get the entire payload,
      ** save the payload in the pC->aRow cache.  That will save us from
      ** having to make additional calls to fetch the content portion of
      ** the record.
      */
      if( avail>=payloadSize ){
        zRec = zData;
        pC->aRow = (u8*)zData;
      }else{
        pC->aRow = 0;
      }
    }
    assert( zRec!=0 || avail>=payloadSize || avail>=9 );
    szHdrSz = GetVarint((u8*)zData, offset);

    /* The KeyFetch() or DataFetch() above are fast and will get the entire
    ** record header in most cases.  But they will fail to get the complete
    ** record header if the record header does not fit on a single page
    ** in the B-Tree.  When that happens, use sqlite3VdbeMemFromBtree() to
    ** acquire the complete header text.
    */
    if( !zRec && avail<offset ){
      rc = sqlite3VdbeMemFromBtree(pCrsr, 0, offset, pC->isIndex, &sMem);
      if( rc!=SQLITE_OK ){
        goto op_column_out;
      }
      zData = sMem.z;
    }
    zEndHdr = (u8 *)&zData[offset];
    zIdx = (u8 *)&zData[szHdrSz];

    /* Scan the header and use it to fill in the aType[] and aOffset[]
    ** arrays.  aType[i] will contain the type integer for the i-th
    ** column and aOffset[i] will contain the offset from the beginning
    ** of the record to the start of the data for the i-th column
    */
    for(i=0; i<nField; i++){
      if( zIdx<zEndHdr ){
        aOffset[i] = offset;
        zIdx += GetVarint(zIdx, aType[i]);
        offset += sqlite3VdbeSerialTypeLen(aType[i]);
      }else{
        /* If i is less that nField, then there are less fields in this
        ** record than SetNumColumns indicated there are columns in the
        ** table. Set the offset for any extra columns not present in
        ** the record to 0. This tells code below to push a NULL onto the
        ** stack instead of deserializing a value from the record.
        */
        aOffset[i] = 0;
      }
    }
    Release(&sMem);
    sMem.flags = MEM_Null;

    /* If we have read more header data than was contained in the header,
    ** or if the end of the last field appears to be past the end of the
    ** record, then we must be dealing with a corrupt database.
    */
    if( zIdx>zEndHdr || offset>payloadSize ){
      rc = SQLITE_CORRUPT_BKPT;
      goto op_column_out;
    }
  }

  /* Get the column information. If aOffset[p2] is non-zero, then 
  ** deserialize the value from the record. If aOffset[p2] is zero,
  ** then there are not enough fields in the record to satisfy the
  ** request.  In this case, set the value NULL or to P3 if P3 is
  ** a pointer to a Mem object.
  */
  if( aOffset[p2] ){
    assert( rc==SQLITE_OK );
    if( zRec ){
      zData = &zRec[aOffset[p2]];
    }else{
      len = sqlite3VdbeSerialTypeLen(aType[p2]);
      rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len, pC->isIndex,&sMem);
      if( rc!=SQLITE_OK ){
        goto op_column_out;
      }
      zData = sMem.z;
    }
    sqlite3VdbeSerialGet((u8*)zData, aType[p2], pTos);
    pTos->enc = encoding;
  }else{
    if( pOp->p3type==P3_MEM ){
      sqlite3VdbeMemShallowCopy(pTos, (Mem *)(pOp->p3), MEM_Static);
    }else{
      pTos->flags = MEM_Null;
    }
  }

  /* If we dynamically allocated space to hold the data (in the
  ** sqlite3VdbeMemFromBtree() call above) then transfer control of that
  ** dynamically allocated space over to the pTos structure.
  ** This prevents a memory copy.
  */
  if( (sMem.flags & MEM_Dyn)!=0 ){
    assert( pTos->flags & MEM_Ephem );
    assert( pTos->flags & (MEM_Str|MEM_Blob) );
    assert( pTos->z==sMem.z );
    assert( sMem.flags & MEM_Term );
    pTos->flags &= ~MEM_Ephem;
    pTos->flags |= MEM_Dyn|MEM_Term;
  }

  /* pTos->z might be pointing to sMem.zShort[].  Fix that so that we
  ** can abandon sMem */
  rc = sqlite3VdbeMemMakeWriteable(pTos);

op_column_out:
  break;
}

/* Opcode: MakeRecord P1 P2 P3
**
** Convert the top abs(P1) entries of the stack into a single entry
** suitable for use as a data record in a database table or as a key
** in an index.  The details of the format are irrelavant as long as
** the OP_Column opcode can decode the record later and as long as the
** sqlite3VdbeRecordCompare function will correctly compare two encoded
** records.  Refer to source code comments for the details of the record
** format.
**
** The original stack entries are popped from the stack if P1>0 but
** remain on the stack if P1<0.
**
** If P2 is not zero and one or more of the entries are NULL, then jump
** to the address given by P2.  This feature can be used to skip a
** uniqueness test on indices.
**
** P3 may be a string that is P1 characters long.  The nth character of the
** string indicates the column affinity that should be used for the nth
** field of the index key (i.e. the first character of P3 corresponds to the
** lowest element on the stack).
**
** The mapping from character to affinity is given by the SQLITE_AFF_
** macros defined in sqliteInt.h.
**
** If P3 is NULL then all index fields have the affinity NONE.
**
** See also OP_MakeIdxRec
*/
/* Opcode: MakeIdxRec P1 P2 P3
**
** This opcode works just OP_MakeRecord except that it reads an extra
** integer from the stack (thus reading a total of abs(P1+1) entries)
** and appends that extra integer to the end of the record as a varint.
** This results in an index key.
*/
case OP_MakeIdxRec:
case OP_MakeRecord: {
  /* Assuming the record contains N fields, the record format looks
  ** like this:
  **
  ** ------------------------------------------------------------------------
  ** | hdr-size | type 0 | type 1 | ... | type N-1 | data0 | ... | data N-1 | 
  ** ------------------------------------------------------------------------
  **
  ** Data(0) is taken from the lowest element of the stack and data(N-1) is
  ** the top of the stack.
  **
  ** Each type field is a varint representing the serial type of the 
  ** corresponding data element (see sqlite3VdbeSerialType()). The
  ** hdr-size field is also a varint which is the offset from the beginning
  ** of the record to data0.
  */
  unsigned char *zNewRecord;
  unsigned char *zCsr;
  Mem *pRec;
  Mem *pRowid = 0;
  int nData = 0;         /* Number of bytes of data space */
  int nHdr = 0;          /* Number of bytes of header space */
  int nByte = 0;         /* Space required for this record */
  int nVarint;           /* Number of bytes in a varint */
  u32 serial_type;       /* Type field */
  int containsNull = 0;  /* True if any of the data fields are NULL */
  char zTemp[NBFS];      /* Space to hold small records */
  Mem *pData0;

  int leaveOnStack;      /* If true, leave the entries on the stack */
  int nField;            /* Number of fields in the record */
  int jumpIfNull;        /* Jump here if non-zero and any entries are NULL. */
  int addRowid;          /* True to append a rowid column at the end */
  char *zAffinity;       /* The affinity string for the record */
  int file_format;       /* File format to use for encoding */

  leaveOnStack = ((pOp->p1<0)?1:0);
  nField = pOp->p1 * (leaveOnStack?-1:1);
  jumpIfNull = pOp->p2;
  addRowid = pOp->opcode==OP_MakeIdxRec;
  zAffinity = pOp->p3;

  pData0 = &pTos[1-nField];
  assert( pData0>=p->aStack );
  containsNull = 0;
  file_format = p->minWriteFileFormat;

  /* Loop through the elements that will make up the record to figure
  ** out how much space is required for the new record.
  */
  for(pRec=pData0; pRec<=pTos; pRec++){
    if( zAffinity ){
      applyAffinity(pRec, zAffinity[pRec-pData0], encoding);
    }
    if( pRec->flags&MEM_Null ){
      containsNull = 1;
    }
    serial_type = sqlite3VdbeSerialType(pRec, file_format);
    nData += sqlite3VdbeSerialTypeLen(serial_type);
    nHdr += sqlite3VarintLen(serial_type);
  }

  /* If we have to append a varint rowid to this record, set 'rowid'
  ** to the value of the rowid and increase nByte by the amount of space
  ** required to store it and the 0x00 seperator byte.
  */
  if( addRowid ){
    pRowid = &pTos[0-nField];
    assert( pRowid>=p->aStack );
    sqlite3VdbeMemIntegerify(pRowid);
    serial_type = sqlite3VdbeSerialType(pRowid, 0);
    nData += sqlite3VdbeSerialTypeLen(serial_type);
    nHdr += sqlite3VarintLen(serial_type);
  }

  /* Add the initial header varint and total the size */
  nHdr += nVarint = sqlite3VarintLen(nHdr);
  if( nVarint<sqlite3VarintLen(nHdr) ){
    nHdr++;
  }
  nByte = nHdr+nData;

  /* Allocate space for the new record. */
  if( nByte>sizeof(zTemp) ){
    zNewRecord = sqliteMallocRaw(nByte);
    if( !zNewRecord ){
      goto no_mem;
    }
  }else{
    zNewRecord = (u8*)zTemp;
  }

  /* Write the record */
  zCsr = zNewRecord;
  zCsr += sqlite3PutVarint(zCsr, nHdr);
  for(pRec=pData0; pRec<=pTos; pRec++){
    serial_type = sqlite3VdbeSerialType(pRec, file_format);
    zCsr += sqlite3PutVarint(zCsr, serial_type);      /* serial type */
  }
  if( addRowid ){
    zCsr += sqlite3PutVarint(zCsr, sqlite3VdbeSerialType(pRowid, 0));
  }
  for(pRec=pData0; pRec<=pTos; pRec++){
    zCsr += sqlite3VdbeSerialPut(zCsr, pRec, file_format);  /* serial data */
  }
  if( addRowid ){
    zCsr += sqlite3VdbeSerialPut(zCsr, pRowid, 0);
  }
  assert( zCsr==(zNewRecord+nByte) );

  /* Pop entries off the stack if required. Push the new record on. */
  if( !leaveOnStack ){
    popStack(&pTos, nField+addRowid);
  }
  pTos++;
  pTos->n = nByte;
  if( nByte<=sizeof(zTemp) ){
    assert( zNewRecord==(unsigned char *)zTemp );
    pTos->z = pTos->zShort;
    memcpy(pTos->zShort, zTemp, nByte);
    pTos->flags = MEM_Blob | MEM_Short;
  }else{
    assert( zNewRecord!=(unsigned char *)zTemp );
    pTos->z = (char*)zNewRecord;
    pTos->flags = MEM_Blob | MEM_Dyn;
    pTos->xDel = 0;
  }
  pTos->enc = SQLITE_UTF8;  /* In case the blob is ever converted to text */

  /* If a NULL was encountered and jumpIfNull is non-zero, take the jump. */
  if( jumpIfNull && containsNull ){
    pc = jumpIfNull - 1;
  }
  break;
}

/* Opcode: Statement P1 * *
**
** Begin an individual statement transaction which is part of a larger
** BEGIN..COMMIT transaction.  This is needed so that the statement
** can be rolled back after an error without having to roll back the
** entire transaction.  The statement transaction will automatically
** commit when the VDBE halts.
**
** The statement is begun on the database file with index P1.  The main
** database file has an index of 0 and the file used for temporary tables
** has an index of 1.
*/
case OP_Statement: {       /* no-push */
  int i = pOp->p1;
  Btree *pBt;
  if( i>=0 && i<db->nDb && (pBt = db->aDb[i].pBt)!=0 && !(db->autoCommit) ){
    assert( sqlite3BtreeIsInTrans(pBt) );
    if( !sqlite3BtreeIsInStmt(pBt) ){
      rc = sqlite3BtreeBeginStmt(pBt);
    }
  }
  break;
}

/* Opcode: AutoCommit P1 P2 *
**
** Set the database auto-commit flag to P1 (1 or 0). If P2 is true, roll
** back any currently active btree transactions. If there are any active
** VMs (apart from this one), then the COMMIT or ROLLBACK statement fails.
**
** This instruction causes the VM to halt.
*/
case OP_AutoCommit: {       /* no-push */
  u8 i = pOp->p1;
  u8 rollback = pOp->p2;

  assert( i==1 || i==0 );
  assert( i==1 || rollback==0 );

  assert( db->activeVdbeCnt>0 );  /* At least this one VM is active */

  if( db->activeVdbeCnt>1 && i && !db->autoCommit ){
    /* If this instruction implements a COMMIT or ROLLBACK, other VMs are
    ** still running, and a transaction is active, return an error indicating
    ** that the other VMs must complete first. 
    */
    sqlite3SetString(&p->zErrMsg, "cannot ", rollback?"rollback":"commit", 
        " transaction - SQL statements in progress", (char*)0);
    rc = SQLITE_ERROR;
  }else if( i!=db->autoCommit ){
    if( pOp->p2 ){
      assert( i==1 );
      sqlite3RollbackAll(db);
      db->autoCommit = 1;
    }else{
      db->autoCommit = i;
      if( sqlite3VdbeHalt(p)==SQLITE_BUSY ){
        p->pTos = pTos;
        p->pc = pc;
        db->autoCommit = 1-i;
        p->rc = SQLITE_BUSY;
        return SQLITE_BUSY;
      }
    }
    return SQLITE_DONE;
  }else{
    sqlite3SetString(&p->zErrMsg,
        (!i)?"cannot start a transaction within a transaction":(
        (rollback)?"cannot rollback - no transaction is active":
                   "cannot commit - no transaction is active"), (char*)0);
         
    rc = SQLITE_ERROR;
  }
  break;
}

/* Opcode: Transaction P1 P2 *
**
** Begin a transaction.  The transaction ends when a Commit or Rollback
** opcode is encountered.  Depending on the ON CONFLICT setting, the
** transaction might also be rolled back if an error is encountered.
**
** P1 is the index of the database file on which the transaction is
** started.  Index 0 is the main database file and index 1 is the
** file used for temporary tables.
**
** If P2 is non-zero, then a write-transaction is started.  A RESERVED lock is
** obtained on the database file when a write-transaction is started.  No
** other process can start another write transaction while this transaction is
** underway.  Starting a write transaction also creates a rollback journal. A
** write transaction must be started before any changes can be made to the
** database.  If P2 is 2 or greater then an EXCLUSIVE lock is also obtained
** on the file.
**
** If P2 is zero, then a read-lock is obtained on the database file.
*/
case OP_Transaction: {       /* no-push */
  int i = pOp->p1;
  Btree *pBt;

  assert( i>=0 && i<db->nDb );
  pBt = db->aDb[i].pBt;

  if( pBt ){
    rc = sqlite3BtreeBeginTrans(pBt, pOp->p2);
    if( rc==SQLITE_BUSY ){
      p->pc = pc;
      p->rc = SQLITE_BUSY;
      p->pTos = pTos;
      return SQLITE_BUSY;
    }
    if( rc!=SQLITE_OK && rc!=SQLITE_READONLY /* && rc!=SQLITE_BUSY */ ){
      goto abort_due_to_error;
    }
  }
  break;
}

/* Opcode: ReadCookie P1 P2 *
**
** Read cookie number P2 from database P1 and push it onto the stack.
** P2==0 is the schema version.  P2==1 is the database format.
** P2==2 is the recommended pager cache size, and so forth.  P1==0 is
** the main database file and P1==1 is the database file used to store
** temporary tables.
**
** There must be a read-lock on the database (either a transaction
** must be started or there must be an open cursor) before
** executing this instruction.
*/
case OP_ReadCookie: {
  int iMeta;
  assert( pOp->p2<SQLITE_N_BTREE_META );
  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  assert( db->aDb[pOp->p1].pBt!=0 );
  /* The indexing of meta values at the schema layer is off by one from
  ** the indexing in the btree layer.  The btree considers meta[0] to
  ** be the number of free pages in the database (a read-only value)
  ** and meta[1] to be the schema cookie.  The schema layer considers
  ** meta[1] to be the schema cookie.  So we have to shift the index
  ** by one in the following statement.
  */
  rc = sqlite3BtreeGetMeta(db->aDb[pOp->p1].pBt, 1 + pOp->p2, (u32 *)&iMeta);
  pTos++;
  pTos->i = iMeta;
  pTos->flags = MEM_Int;
  break;
}

/* Opcode: SetCookie P1 P2 *
**
** Write the top of the stack into cookie number P2 of database P1.
** P2==0 is the schema version.  P2==1 is the database format.
** P2==2 is the recommended pager cache size, and so forth.  P1==0 is
** the main database file and P1==1 is the database file used to store
** temporary tables.
**
** A transaction must be started before executing this opcode.
*/
case OP_SetCookie: {       /* no-push */
  Db *pDb;
  assert( pOp->p2<SQLITE_N_BTREE_META );
  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  pDb = &db->aDb[pOp->p1];
  assert( pDb->pBt!=0 );
  assert( pTos>=p->aStack );
  sqlite3VdbeMemIntegerify(pTos);
  /* See note about index shifting on OP_ReadCookie */
  rc = sqlite3BtreeUpdateMeta(pDb->pBt, 1+pOp->p2, (int)pTos->i);
  if( pOp->p2==0 ){
    /* When the schema cookie changes, record the new cookie internally */
    pDb->pSchema->schema_cookie = pTos->i;
    db->flags |= SQLITE_InternChanges;
  }else if( pOp->p2==1 ){
    /* Record changes in the file format */
    pDb->pSchema->file_format = pTos->i;
  }
  assert( (pTos->flags & MEM_Dyn)==0 );
  pTos--;
  if( pOp->p1==1 ){
    /* Invalidate all prepared statements whenever the TEMP database
    ** schema is changed.  Ticket #1644 */
    sqlite3ExpirePreparedStatements(db);
  }
  break;
}

/* Opcode: VerifyCookie P1 P2 *
**
** Check the value of global database parameter number 0 (the
** schema version) and make sure it is equal to P2.  
** P1 is the database number which is 0 for the main database file
** and 1 for the file holding temporary tables and some higher number
** for auxiliary databases.
**
** The cookie changes its value whenever the database schema changes.
** This operation is used to detect when that the cookie has changed
** and that the current process needs to reread the schema.
**
** Either a transaction needs to have been started or an OP_Open needs
** to be executed (to establish a read lock) before this opcode is
** invoked.
*/
case OP_VerifyCookie: {       /* no-push */
  int iMeta;
  Btree *pBt;
  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  pBt = db->aDb[pOp->p1].pBt;
  if( pBt ){
    rc = sqlite3BtreeGetMeta(pBt, 1, (u32 *)&iMeta);
  }else{
    rc = SQLITE_OK;
    iMeta = 0;
  }
  if( rc==SQLITE_OK && iMeta!=pOp->p2 ){
    sqlite3SetString(&p->zErrMsg, "database schema has changed", (char*)0);
    rc = SQLITE_SCHEMA;
  }
  break;
}

/* Opcode: OpenRead P1 P2 P3
**
** Open a read-only cursor for the database table whose root page is
** P2 in a database file.  The database file is determined by an 
** integer from the top of the stack.  0 means the main database and
** 1 means the database used for temporary tables.  Give the new 
** cursor an identifier of P1.  The P1 values need not be contiguous
** but all P1 values should be small integers.  It is an error for
** P1 to be negative.
**
** If P2==0 then take the root page number from the next of the stack.
**
** There will be a read lock on the database whenever there is an
** open cursor.  If the database was unlocked prior to this instruction
** then a read lock is acquired as part of this instruction.  A read
** lock allows other processes to read the database but prohibits
** any other process from modifying the database.  The read lock is
** released when all cursors are closed.  If this instruction attempts
** to get a read lock but fails, the script terminates with an
** SQLITE_BUSY error code.
**
** The P3 value is a pointer to a KeyInfo structure that defines the
** content and collating sequence of indices.  P3 is NULL for cursors
** that are not pointing to indices.
**
** See also OpenWrite.
*/
/* Opcode: OpenWrite P1 P2 P3
**
** Open a read/write cursor named P1 on the table or index whose ro