{
  Turbo Pascal Include file to display space remaining on disk.
  Nov. 19, 1986 by Carson Wilson. For all CP/M 2.2 systems.
  ByteMask works on the principle that, e.g., if ByteMask = 00100000 (binary),
  ByteMask AND AllocByte = 1 only if the third bit in AllocByte = 1.

CALLING CONVENTIONS:

writeln(CPMStats('d',space));
                       ...If 'd' is a legal drive letter (see "LegalDrives"
                          below), get space on that drive. If 'd' is an
                          ILLEGAL drive letter, get space remaining on
                          current drive. Output is a number representing
                          the number of kilobytes left.

BLSize := CPMStats('d',size);
                       ...Gets block size of drive, or current drive, where
                          "BLSize" is an integer variable.
}
type
  calltype = (space,size);   { return space on disk, or block size? }

function CPMStats(DriveLtr : char; command : calltype) : integer;
  const
    GetParams = 31;   { BDOS Get Disk Parameters Address }
    GetAlloc  = 27;   {   "  Get Allocation Address      }
    MaxByte   = $80;  { 10000000 binary }
    LegalDrives : set of char = ['A'..'P'];
  type
    table = record         { holds disk parameters block for selected disk }
      SPT : integer;
      BSH, BLM, EXM : byte;
      DSM, DRM : integer;
      AL0, AL1 : byte;
      CKS, OFF : integer;
      end;
  var
    TableArray : table;
    BlockSize,          { size, in Kb, of each data block on disk }
    ByteMask,
    AllocBit,           { 1 bit     within allocation  block }
    AllocByte : byte;   { 1 byte       "       "         "   }
    TableSize,          { length, in bits, of the allocation table }
    offset,
    AllocAddr,          { address of start of allocation block }
    TableAddr,          {    "     "   "   "  disk parameters }
    K : integer;        { calculated disk space in Kb }

  begin
  DriveLtr := upcase(DriveLtr);
  if DriveLtr in LegalDrives then
    bdos(14,ord(DriveLtr) - $41);    { select drive - else use default drive }
  K := 0;
  TableAddr := bdoshl(GetParams);
  AllocAddr := bdoshl(GetAlloc);
  for offset := 0 to 14 do
    mem[addr(TableArray) + offset] :=
    mem[TableAddr + offset];      { move disk parameters into record variable }
                                  {      "TableArray"                         }
  with TableArray do begin
    if DSM > 255 then BlockSize := EXM * 2 + 2
    else BlockSize := EXM + 1;     { see p. 147 of Dig. Res. CP/M 2.2 Manual }
    TableSize := DSM + 1;
    end;

  for offset := 0 to (TableSize div 8 - 1) do begin  { do full bytes in }
    AllocByte := mem[AllocAddr + offset];            { allocation block }
    ByteMask := MaxByte;                    { 10000000B }
    for AllocBit := 1 to 8 do begin
      if AllocByte AND ByteMask = 0 then
        K := K + BlockSize;                 { doesn't match mask }
      ByteMask :=  ByteMask SHR 1;
      end;
    end;

  offset := offset + 1;
  AllocByte := mem[AllocAddr + offset];
  ByteMask := MaxByte;
  for AllocBit := 1 to (TableSize mod 8) do begin   { do remaining allocation }
    if AllocByte AND ByteMask = 0 then K := K + BlockSize;     { bits, if any }
    ByteMask :=  ByteMask SHR 1;
    end;
  case command of
    space : CPMStats := K;
    size  : CPMStats := BlockSize;
    end;
  end;           { function CPMStats }