/* According to some sources, the effect of changing the size of the
  ** underlying file on mapped regions that correspond to the added or
  ** removed pages is undefined. However, there is reason to believe that
  ** on modern platforms like Linux or OSX, things just work. For example,
  ** it is possible to create a mapping larger than the file on disk and
  ** extend the file on disk later on.
  **
  ** Exploit this on OSX to reduce the number of munmap()/mmap() calls
  ** if the file size is changing. In this case all mappings are rounded
  ** up to the nearest 4MB. And if a new mapping is requested that has the
  ** same rounded size as an old mapping, the old mapping can simply be
  ** reused as is.
  **
  ** It would be possible to do the above on Linux too. However, Linux has
  ** the non-standard mremap() call to resize existing mappings, which can
  ** be used instead.  */
#if defined(__APPLE__)
  nNewRnd = ROUNDUP(nNew, 4096*1024);
  nOldRnd = ROUNDUP(nOld, 4096*1024);
#else
  nNewRnd = ROUNDUP(nNew, 4096*1);
  nOldRnd = ROUNDUP(nOld, 4096*1);
#endif

  /* On OSX or Linux, reuse the old mapping if it is the right size. */
#if defined(__APPLE__) || defined(__linux__)
  if( nNewRnd==nOldRnd ){
    return SQLITE_OK;
  }
#endif

  /* On Linux, if there is both an old and new mapping, resize the old 
  ** mapping using the non-standard mremap() call.  */
#if defined(_GNU_SOURCE) && defined(__linux__)
  if( nNewRnd && nOldRnd ){
    void *pOld = *ppMap;
    *ppMap = pNew = mremap(pOld, nOldRnd, nNewRnd, MREMAP_MAYMOVE);
    if( pNew==MAP_FAILED ){
      *ppMap = 0;
      return SQLITE_IOERR_MREMAP;
    }
    return SQLITE_OK;
  }
#endif

  /* If we get this far, unmap any old mapping. */
  if( nOldRnd!=0 ){
    void *pOld = *ppMap;

  /* According to some sources, the effect of changing the size of the
  ** underlying file on mapped regions that correspond to the added or
  ** removed pages is undefined. However, there is reason to believe that
  ** on modern platforms like Linux or OSX, things just work. For example,
  ** it is possible to create a mapping larger than the file on disk and
  ** extend the file on disk later on.
  **
  ** Exploit this on Linux and OSX to reduce the number of munmap()/mmap() 
  ** calls required if the file size is changing. In this case all mappings 
  ** are rounded up to the nearest 4MB. And if a new mapping is requested 
  ** that has the same rounded size as an old mapping, the old mapping can 
  ** be reused as is. */




#if defined(__APPLE__) || defined(__linux__)
  nNewRnd = ROUNDUP(nNew, 4096*1024);
  nOldRnd = ROUNDUP(nOld, 4096*1024);
#else
  nNewRnd = ROUNDUP(nNew, 4096*1);
  nOldRnd = ROUNDUP(nOld, 4096*1);
#endif

  /* On OSX or Linux, reuse the old mapping if it is the right size. */
#if defined(__APPLE__) || defined(__linux__)
  if( nNewRnd==nOldRnd ){














    return SQLITE_OK;
  }
#endif

  /* If we get this far, unmap any old mapping. */
  if( nOldRnd!=0 ){
    void *pOld = *ppMap;