kolibrios/programs/develop/oberon07/Samples/Windows/Console/hailst.ob07

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(*
adapted to Oberon-07 by 0CodErr, KolibriOS team
*)
(*
The Hailstone sequence of numbers can be generated
from a starting positive integer, n by:
IF n is 1 THEN the sequence ends.
IF n is even THEN the next n of the sequence = n / 2
IF n is odd THEN the next n of the sequence = (3 * n) + 1
The (unproven) Collatz conjecture is that the hailstone sequence
for any starting number always terminates.
*)
MODULE hailst;
IMPORT In, Out, API, Console;
CONST
maxCard = ROR(-2, 1) DIV 3;
List = 1;
Count = 2;
Max = 3;
VAR
a: INTEGER;
PROCEDURE HALT(code: INTEGER);
BEGIN
In.Ln; Console.exit(TRUE); API.exit(code)
END HALT;
PROCEDURE HailStone(start, _type: INTEGER): INTEGER;
VAR
n, max, count, res: INTEGER;
exit: BOOLEAN;
BEGIN
count := 1;
n := start;
max := n;
exit := FALSE;
WHILE exit # TRUE DO
IF _type = List THEN
Out.Int (n, 12);
IF count MOD 6 = 0 THEN Out.Ln END
END;
IF n # 1 THEN
IF ODD(n) THEN
IF n < maxCard THEN
n := 3 * n + 1;
IF n > max THEN max := n END
ELSE
Out.String("Exceeding max value for type INTEGER at:");
Out.Ln;
Out.String("n = "); Out.Int(start, 1);
Out.String(", count = "); Out.Int(count, 1);
Out.String(", intermediate value ");
Out.Int(n, 1);
Out.String(". Aborting.");
Out.Ln;
HALT(2)
END
ELSE
n := n DIV 2
END;
INC(count)
ELSE
exit := TRUE
END
END;
IF _type = Max THEN res := max ELSE res := count END
RETURN res
END HailStone;
PROCEDURE FindMax(num: INTEGER);
VAR
val, maxCount, maxVal, cnt: INTEGER;
BEGIN
maxCount := 0;
maxVal := 0;
FOR val := 2 TO num DO
cnt := HailStone(val, Count);
IF cnt > maxCount THEN
maxVal := val;
maxCount := cnt
END
END;
Out.String("Longest sequence below "); Out.Int(num, 1);
Out.String(" is "); Out.Int(HailStone(maxVal, Count), 1);
Out.String(" for n = "); Out.Int(maxVal, 1);
Out.String(" with an intermediate maximum of ");
Out.Int(HailStone(maxVal, Max), 1);
Out.Ln
END FindMax;
BEGIN
Console.open;
a := HailStone(27, List);
Out.Ln;
Out.String("Iterations total = "); Out.Int(HailStone(27, Count), 1);
Out.String(" max value = "); Out.Int(HailStone(27, Max), 1);
Out.Ln;
FindMax(100000);
Out.String("Done.");
Out.Ln; In.Ln;
Console.exit(TRUE)
END hailst.