Sip from the Firehose

If you try the Randomize procedure in Turbo Pascal version 1.0, you will notice that it doesn’t do anything at all.  The original manual says it will re-seed the random number generator function so that it doesn’t start with the same random numbers each time.

In the Turbo Tutor version 1 book, section 20.1, there is a replacement for the Randomize procedure.  Here is the text from the chapter about MS-DOS Routines and DOS function calls:

20.1 RANDOMIZE (RANDOM.PAS)

We’ll start with fixing a problen in TURBO Pascal.  As you may have noticed, the procedure Randomize does nothing at all in TuRBO.  Here is a procedure for MS-DOS and PC-DOS that replaces the built in Randomize with a working version.

The new Randomize has two Integer parameters.  If they are both 0, then the random number seed is set randomly.  If either of the parameters is nonzero, then they are both stored directly into the 32 bit seed.

To set the seed randomly (Randomize(0,0)), the procedure calls MS-DOS to get the current time.  This is a 32 bit value, which is also stored directly into the seed.  On some systems, (i.e. the NCR Decision Mate V) the clock does not tick, so the time never changes.  Randomize checks this, and if the clock hasn’t changed after a Delay(100), it asks the user to hit a key.  While waiting for the key, it continuously increments two counters.  These are then stored into the seed.

Please note:  This routine is for MS-DOC/PC-DOS TURBO ONLY!

program RandomTest;
{
    This program tests out the Randomize procedure.  It also
    calculates a chi-aquare value as a test of Random itself.
    Chi-square values between 3 and 16 are desirable with
    values close to 8.3 being optimum.
}
var
  S1,S2,Indx,Jndx,Count : Integer;
  Sum,T,NP : Real;
  Tally : array[0..9] of Integer;

procedure Randomize(I,J: Integer);
var
  RSet : record
    AX,BX,CX,DX,BP,SI,DI,DS,ES,Flags: Integer;
  end;
  Ch : Char;
begin
  if (I=0) and (J=0) then begin  { Generate a random number seed}
    RSet.AX := $2C00;
    MSDos(RSet);  { DOS time of day function }
    I := RSet.CX;
    J := RSet.DX;
    Delay(100); { This delay may have to be increased for faster systems }
    MSDos(RSet);
    if (I=RSet.CX) and (J=RSet.DX) then begin     { Clock isn't ticking }
      I := 0;
      J := 0;
      while KeyPressed do
        Read(Kbd,Ch);          { clear keyboard buffer }
      Write('Hit any key to set the random number generator: ');
      repeat
        I := I + 13;
        J := J + 17
      until KeyPressed;
      Read(Kbd,Ch);            { Absorb the character }
      WriteLn
    end
  end;
  MemW[DSeg:$0129] := I;    { This is the core of the reoutine: store a 32 bit }
  MemW[DSeg:$012B] := J;    {  seed at locations DSeg:$0129...DSeg:$012B }
end;  { of procedure Randomize }

begin  { main body of program RandomTest }
  Writeln('Enter count  0 then begin      { do random number test }
      Write('Enter seeds (S1 S2):  ');    { get 2 integers for seed }
      ReadLn(S1,S2);
      Randomize(S1,S2);    { set random number seed }
      FillChar(Tally, SizeOf(Tally),0);   { Clear Tally array }
      for Indx := 1 to Count do begin    { generate Count numbers }
        Jndx := Random(10);             { range is 0..9 }
        Tally[Jndx] := Tally[Jndx] + 1;  { count how many of each }
      end;
      Sum := 0.0;     { Clear sum for X^2 }
      NP := Count/10.0;    { theoretical number for each }
      for Indx := 0 to 9 do begin  { for each possible result do }
        Write(Tally[Indx]:5);      { write total for that value }
        Sum := Sum + Sqr(Tally[Indx]-NP)/NP    { and calculate X^2 }
      end;
      Writeln;
      Writeln('Chi-Square (9 degreed of freedon) = ',Sum:8:3)
    end
  until Count <= 0
end.  { of program RandomTest }

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