SQLite

** [sqlite3_exec()], [sqlite3_step()] and [sqlite3_get_table()] for
** database connection D.  An example use for this
** interface is to keep a GUI updated during a large query.
**
** ^The parameter P is passed through as the only parameter to the 
** callback function X.  ^The parameter N is the approximate number of 
** [virtual machine instructions] that are evaluated between successive
** invocations of the callback X.  ^If N is less than one then the progress
** handler is disabled.
**
** ^Only a single progress handler may be defined at one time per
** [database connection]; setting a new progress handler cancels the
** old one.  ^Setting parameter X to NULL disables the progress handler.
** ^The progress handler is also disabled by setting N to a value less
** than 1.
**

  int rc = SQLITE_OK;        /* Value to return */
  sqlite3 *db = p->db;       /* The database */
  u8 resetSchemaOnFault = 0; /* Reset schema after an error if positive */
  u8 encoding = ENC(db);     /* The database encoding */
  int iCompare = 0;          /* Result of last OP_Compare operation */
  unsigned nVmStep = 0;      /* Number of virtual machine steps */
#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
  unsigned nProgressLimit;   /* Invoke xProgress() when nVmStep reaches this */
#endif
  Mem *aMem = p->aMem;       /* Copy of p->aMem */
  Mem *pIn1 = 0;             /* 1st input operand */
  Mem *pIn2 = 0;             /* 2nd input operand */
  Mem *pIn3 = 0;             /* 3rd input operand */
  Mem *pOut = 0;             /* Output operand */
  int *aPermute = 0;         /* Permutation of columns for OP_Compare */

  assert( p->bIsReader || p->readOnly!=0 );
  p->rc = SQLITE_OK;
  assert( p->explain==0 );
  p->pResultSet = 0;
  db->busyHandler.nBusy = 0;
  CHECK_FOR_INTERRUPT;
  sqlite3VdbeIOTraceSql(p);
#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
  if( db->xProgress ){
    assert( 0 < db->nProgressOps );
    nProgressLimit = (unsigned)p->aCounter[SQLITE_STMTSTATUS_VM_STEP-1];
    if( nProgressLimit==0 ){
      nProgressLimit = db->nProgressOps;
    }else{
      nProgressLimit %= (unsigned)db->nProgressOps;
    }
  }
#endif
#ifdef SQLITE_DEBUG
  sqlite3BeginBenignMalloc();
  if( p->pc==0  && (p->db->flags & SQLITE_VdbeListing)!=0 ){
    int i;
    printf("VDBE Program Listing:\n");
    sqlite3VdbePrintSql(p);
    for(i=0; i<p->nOp; i++){

#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!=0 && nVmStep>=nProgressLimit ){
    int prc;
    prc = db->xProgress(db->pProgressArg);
    if( prc!=0 ){
      rc = SQLITE_INTERRUPT;
      goto vdbe_error_halt;
    }
    if( db->xProgress!=0 ){
      nProgressLimit = nVmStep + db->nProgressOps - (nVmStep%db->nProgressOps);
    }
  }
#endif
  
  break;
}

/* Opcode:  Gosub P1 P2 * * *