Shareware Grab Bag/Shareware Grab Bag.iso/007/strucpgm.arc/ERAT.SP

Text File | 1983-10-25 | 1.6 KB | 70 lines

BEGIN
    COMMENT Sieve of Eratosthenes program to calculate
        prime numbers. ;


    REAL Time_in_seconds; { Output argument of PROCEDURE
                Compute_time_in_seconds.        }

    PROCEDURE Compute_time_in_seconds;
    BEGIN
        STRING Time_string; { This holds the current time. }

        Time_string:=TIME$; { HH:MM:SS }
        Time_in_seconds:=VAL(MID$(Time_string,1,2))*3600 {Hours * 3600}
            +VAL(MID$(Time_string,4,2))*60  {Minutes*60 added}
            +VAL(MID$(Time_string,7,2)); {Seconds added}

        { The time in seconds are now computed. }
    END


    INTEGER ARRAY FLAGS(8191); {Prime number flags.}

    INTEGER I,M,K,PRIME,COUNT; {Loop variables,prime number counter.}

    REAL Start_time,        {Start time of test}
         Finish_time;       {Finish time for ten iterations.}

    Compute_time_in_seconds; {Compute the current time.}
    Start_time:=Time_in_seconds; {Set Start time.}

    OUTPUT('Time is:' + TIME$);

    FOR M := 1 STEP 1 UNTIL 10 DO
    BEGIN
        COUNT := 0;

        FOR I := 1 STEP 1 UNTIL 8191 DO
        BEGIN
            FLAGS(I) := 1;
        END

        FOR I := 1 STEP 1 UNTIL 8191 DO
        BEGIN
            IF FLAGS(I) = 1 THEN
            BEGIN
                PRIME := I+I+3;
                K := I+PRIME;

                WHILE K <= 8191 DO
                BEGIN
                    FLAGS(K) := 0;
                    K := K+PRIME;
                END

                COUNT := COUNT+1;
            END
        END
    END

    Compute_time_in_seconds; {Compute the current time.}
    Finish_time:=Time_in_seconds; {Set Finish time.}

    OUTPUT('Time is:' + TIME$); OUTPUT();
    OUTPUT(COUNT @ ' PRIMES for each of Ten iterations.'); OUTPUT();
    OUTPUT('Time for one iteration is:' @
         (Finish_time - Start_time)/10.
        @ ' seconds.');
END