- Speed test. Clarification

From: [at]} <Rex>
Date: Fri, 03 Nov 2006 15:05:05 -0600

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        That ought to teach me not to post partial code. The complete programs are posted below (I added timers).

        I made the arrays big, (1) so I didn't have to bother with timers in three compilers, and (2) to make sure they wouldn't fit in the cache. For comparing compilers, I wanted to avoid erratic results due to the cache.

        I like Wojtek's program, though. Caching makes almost a threefold improvement in speed on my computer, so yes, memory is the bottleneck.

        I played a little more with unrolling the loop. Unrolling 5 times gave an 18% improvement with an array length of 100, but it was 2% worse with a length of 1,000,000. Your mileage may vary.

        There is one other inconvenient truth, however. With the FORTRAN program, with an array size of around 15,000 or lower (number of arithmetic operations constant), so everything fit in the cache, the operation was astonishingly fast -- 2 1/2 seconds, compared to 10 seconds at best for BB. But again, that's an unfair comparison, because with range checking, FORTRAN takes 10 minutes 30 seconds!

Rex Couture

=======
MODULE TestTime;
IMPORT StdLog, Services;

VAR
        a, b: ARRAY 1000000 OF REAL;
        i, j: INTEGER;
        sum: REAL;
        t0: LONGINT;

PROCEDURE Do*;
BEGIN
t0:= Services.Ticks();
sum:= 0;
FOR j:= 0 TO 199 DO
        FOR i:= 0 TO 999999 DO
                a[i]:= i-j;
                b[i]:= i-j;
                END;
        FOR i:= 0 TO 999999 DO
                sum:= sum +a[i]*b[i];
                END;
        END;
StdLog.Int((Services.Ticks() - t0));
StdLog.Real( sum); StdLog.Ln
END Do;

========
MODULE TestTime2; (* Unrolls loop *)

IMPORT StdLog, Services;

VAR
        a, b: ARRAY 1000000 OF REAL;
        i, j: INTEGER;
        sum: REAL;
        t0: LONGINT;

PROCEDURE Do*;
BEGIN
t0:= Services.Ticks();
sum:= 0;
FOR j:= 0 TO 199 DO
        FOR i:= 0 TO 999999 BY 5 DO
                a[i]:= i-j;
                b[i]:= i-j;
                a[i+1]:= i-j;
                b[i+1]:= i-j;
                a[i+2]:= i-j;
                b[i+2]:= i-j;
                a[i+3]:= i-j;
                b[i+3]:= i-j;
                a[i+4]:= i-j;
                b[i+4]:= i-j;
                END;
        FOR i:= 0 TO 999999 BY 5 DO
                sum:= sum +a[i]*b[i];
                sum:= sum +a[i+1]*b[i+1];
                sum:= sum +a[i+2]*b[i+2];
                sum:= sum +a[i+3]*b[i+3];
                sum:= sum +a[i+4]*b[i+4];
                END;
        END;
StdLog.Int((Services.Ticks() - t0));
StdLog.Real( sum); StdLog.Ln
END Do;

END TestTime2.

--- BlackBox
--- send subject HELP or UNSUBSCRIBE to blackbox{([at]})nowhere.xy


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Received on Fri Nov 03 2006 - 22:05:05 UTC