🚀 go-pugleaf

netnews@altavista.net wrote:
> 
> In article <7f4grb$7ik$1@nnrp1.dejanews.com>,
>   Robert AH Prins <prinsra@williscorroon.com> wrote:
> > In reply to a private email from a person who knows he can interrupt me. (but
> > should have added to the tread...)

  'Twas me  - hit the wrong button in Netscape. Sorry. By  the  time I
  noticed, it was too late to do anything about it.

  [...]

  >> If your  file  exceeds available direct access  memory,  you will
  >> have to  settle  for a multipass merge sort,  in  very simplistic
  >> terms:

  >> - read in as many records as allowed by available RAM
  >> - sort them and write them out to file 1
  >> - read in a next bunch of records
  >> - sort them and write them out to file 2
  >> - repeat above until entire original file has been processed.
  >> - open files created
  >> - read one record from each of them
  >> - write out the smallest of these and read the next record from the
  >>   file that delivered it
  >> - repeat previous step until all files have reached eof

  [...]

  Very good explanation. Thanks!

  The key  is  to "write out the smallest of these and  read  the next
  record *from the file that delivered it*". It didn't make  any sense
  until that sunk in.

  The next problem is the number of file handles. This might be a good
  argument for not using the heap, which limits you to 64k chunks.

  Instead, allocate  DOS  memory with int21, function  48.  This would
  allow sorting in ~500k chunks. If you had 30 file handles available,
  this would allow sorting files up to 15 megabytes before running out
  of file handles.

  Thanks to  WIN9X, most machines come with 64 or 128 megs of  ram. It
  seems you  could  use Himem to move data from DOS to  XMS,  and sort
  larger files by using XMS instead of writing to the hard disk.

  Of course, the ideal would be to use flat real mode and do  the sort
  directly in ram! Default to using Himem only when in V86 mode.

Best Regards,

Michael R. Monett,
Automated Production Test
mailto:add@csolve.net