SQLite

** An rtree virtual-table object.
*/
struct Rtree {
  sqlite3_vtab base;          /* Base class.  Must be first */
  sqlite3 *db;                /* Host database connection */
  int iNodeSize;              /* Size in bytes of each node in the node table */
  u8 nDim;                    /* Number of dimensions */
  u8 nDim2;                   /* Twice the number of dimensions */
  u8 eCoordType;              /* RTREE_COORD_REAL32 or RTREE_COORD_INT32 */
  u8 nBytesPerCell;           /* Bytes consumed per cell */
  int iDepth;                 /* Current depth of the r-tree structure */
  char *zDb;                  /* Name of database containing r-tree table */
  char *zName;                /* Name of r-tree table */ 
  int nBusy;                  /* Current number of users of this structure */
  i64 nRowEst;                /* Estimated number of rows in this table */

  RtreeNode *pNode,          /* The node into which the cell is to be written */
  RtreeCell *pCell,          /* The cell to write */
  int iCell                  /* Index into pNode into which pCell is written */
){
  int ii;
  u8 *p = &pNode->zData[4 + pRtree->nBytesPerCell*iCell];
  p += writeInt64(p, pCell->iRowid);
  for(ii=0; ii<pRtree->nDim2; ii++){
    p += writeCoord(p, &pCell->aCoord[ii]);
  }
  pNode->isDirty = 1;
}

/*
** Remove the cell with index iCell from node pNode.

  pData = pNode->zData + (12 + pRtree->nBytesPerCell*iCell);
  pCoord = pCell->aCoord;
  do{
    readCoord(pData, &pCoord[ii]);
    readCoord(pData+4, &pCoord[ii+1]);
    pData += 8;
    ii += 2;
  }while( ii<pRtree->nDim2 );
}


/* Forward declaration for the function that does the work of
** the virtual table module xCreate() and xConnect() methods.
*/
static int rtreeInit(

            ** can be cast into an RtreeMatchArg object. One created using
            ** an sqlite3_rtree_geometry_callback() SQL user function.
            */
            rc = deserializeGeometry(argv[ii], p);
            if( rc!=SQLITE_OK ){
              break;
            }
            p->pInfo->nCoord = pRtree->nDim2;
            p->pInfo->anQueue = pCsr->anQueue;
            p->pInfo->mxLevel = pRtree->iDepth + 1;
          }else{
#ifdef SQLITE_RTREE_INT_ONLY
            p->u.rValue = sqlite3_value_int64(argv[ii]);
#else
            p->u.rValue = sqlite3_value_double(argv[ii]);

  return rc;
}

/*
** Return the N-dimensional volumn of the cell stored in *p.
*/
static RtreeDValue cellArea(Rtree *pRtree, RtreeCell *p){
  RtreeDValue area;
  int ii;
  area = DCOORD(p->aCoord[1]) - DCOORD(p->aCoord[0]);
  for(ii=2; ii<pRtree->nDim2; ii+=2){
    area *= DCOORD(p->aCoord[ii+1]) - DCOORD(p->aCoord[ii]);
  }
  return area;
}

/*
** Return the margin length of cell p. The margin length is the sum
** of the objects size in each dimension.
*/
static RtreeDValue cellMargin(Rtree *pRtree, RtreeCell *p){
  RtreeDValue margin;
  int ii;
  margin = DCOORD(p->aCoord[1]) - DCOORD(p->aCoord[0]);
  for(ii=2; ii<pRtree->nDim2; ii+=2){
    margin += (DCOORD(p->aCoord[ii+1]) - DCOORD(p->aCoord[ii]));
  }
  return margin;
}

/*
** Store the union of cells p1 and p2 in p1.
*/
static void cellUnion(Rtree *pRtree, RtreeCell *p1, RtreeCell *p2){
  int ii = 0;
  if( pRtree->eCoordType==RTREE_COORD_REAL32 ){
    do{
      p1->aCoord[ii].f = MIN(p1->aCoord[ii].f, p2->aCoord[ii].f);
      p1->aCoord[ii+1].f = MAX(p1->aCoord[ii+1].f, p2->aCoord[ii+1].f);

      ii += 2;
    }while( ii<pRtree->nDim2 );
  }else{

    do{
      p1->aCoord[ii].i = MIN(p1->aCoord[ii].i, p2->aCoord[ii].i);
      p1->aCoord[ii+1].i = MAX(p1->aCoord[ii+1].i, p2->aCoord[ii+1].i);

      ii += 2;
    }while( ii<pRtree->nDim2 );
  }
}

/*
** Return true if the area covered by p2 is a subset of the area covered
** by p1. False otherwise.
*/
static int cellContains(Rtree *pRtree, RtreeCell *p1, RtreeCell *p2){
  int ii;
  int isInt = (pRtree->eCoordType==RTREE_COORD_INT32);
  for(ii=0; ii<pRtree->nDim2; ii+=2){
    RtreeCoord *a1 = &p1->aCoord[ii];
    RtreeCoord *a2 = &p2->aCoord[ii];
    if( (!isInt && (a2[0].f<a1[0].f || a2[1].f>a1[1].f)) 
     || ( isInt && (a2[0].i<a1[0].i || a2[1].i>a1[1].i)) 
    ){
      return 0;
    }

  int nCell
){
  int ii;
  RtreeDValue overlap = RTREE_ZERO;
  for(ii=0; ii<nCell; ii++){
    int jj;
    RtreeDValue o = (RtreeDValue)1;
    for(jj=0; jj<pRtree->nDim2; jj+=2){
      RtreeDValue x1, x2;
      x1 = MAX(DCOORD(p->aCoord[jj]), DCOORD(aCell[ii].aCoord[jj]));
      x2 = MIN(DCOORD(p->aCoord[jj+1]), DCOORD(aCell[ii].aCoord[jj+1]));
      if( x2<x1 ){
        o = (RtreeDValue)0;
        break;
      }else{

    **
    ** NB: nData can only be less than nDim*2+3 if the rtree is mis-declared
    ** with "column" that are interpreted as table constraints.
    ** Example:  CREATE VIRTUAL TABLE bad USING rtree(x,y,CHECK(y>5));
    ** This problem was discovered after years of use, so we silently ignore
    ** these kinds of misdeclared tables to avoid breaking any legacy.
    */
    assert( nData<=(pRtree->nDim2 + 3) );

#ifndef SQLITE_RTREE_INT_ONLY
    if( pRtree->eCoordType==RTREE_COORD_REAL32 ){
      for(ii=0; ii<nData-4; ii+=2){
        cell.aCoord[ii].f = rtreeValueDown(azData[ii+3]);
        cell.aCoord[ii+1].f = rtreeValueUp(azData[ii+4]);
        if( cell.aCoord[ii].f>cell.aCoord[ii+1].f ){

  }
  memset(pRtree, 0, sizeof(Rtree)+nDb+nName+2);
  pRtree->nBusy = 1;
  pRtree->base.pModule = &rtreeModule;
  pRtree->zDb = (char *)&pRtree[1];
  pRtree->zName = &pRtree->zDb[nDb+1];
  pRtree->nDim = (argc-4)/2;
  pRtree->nDim2 = argc - 4;
  pRtree->nBytesPerCell = 8 + pRtree->nDim2*4;
  pRtree->eCoordType = eCoordType;
  memcpy(pRtree->zDb, argv[1], nDb);
  memcpy(pRtree->zName, argv[2], nName);

  /* Figure out the node size to use. */
  rc = getNodeSize(db, pRtree, isCreate, pzErr);

  Rtree tree;
  int ii;

  UNUSED_PARAMETER(nArg);
  memset(&node, 0, sizeof(RtreeNode));
  memset(&tree, 0, sizeof(Rtree));
  tree.nDim = sqlite3_value_int(apArg[0]);
  tree.nDim2 = tree.nDim*2;
  tree.nBytesPerCell = 8 + 8 * tree.nDim;
  node.zData = (u8 *)sqlite3_value_blob(apArg[1]);

  for(ii=0; ii<NCELL(&node); ii++){
    char zCell[512];
    int nCell = 0;
    RtreeCell cell;
    int jj;

    nodeGetCell(&tree, &node, ii, &cell);
    sqlite3_snprintf(512-nCell,&zCell[nCell],"%lld", cell.iRowid);
    nCell = (int)strlen(zCell);
    for(jj=0; jj<tree.nDim2; jj++){
#ifndef SQLITE_RTREE_INT_ONLY
      sqlite3_snprintf(512-nCell,&zCell[nCell], " %g",
                       (double)cell.aCoord[jj].f);
#else
      sqlite3_snprintf(512-nCell,&zCell[nCell], " %d",
                       cell.aCoord[jj].i);
#endif