thx for the answers so far!
multithreading:
Am Samstag, 1. Juli 2017 15:07:37 UTC+2 schrieb Shakin Billy:
> hi,
>
> i've been working a little on project euler problem 501.
> my first attempt is a burte forcce loop.4iw rote it in java und racket and
> found java to be faster by factor 3:
>
> racket
>
> #lang typed/racket
> (require racket/unsafe/ops)
> (require racket/fixnum)
> (require racket/trace)
> ;(require typed/racket/performance-hint)
>
> (: acht-teiler (-> Fixnum Boolean))
> (define (acht-teiler (n : Fixnum))
> (: loop (-> Fixnum Fixnum Fixnum Fixnum Boolean))
> (define (loop (i : Fixnum) (count : Fixnum) (quadrat : Fixnum) (steigung :
> Fixnum))
> (cond ((unsafe-fx= quadrat n) #f)
> ((unsafe-fx> quadrat n) (unsafe-fx= count 3))
> ((unsafe-fx= (unsafe-fxmodulo n i) 0) (loop (unsafe-fx+ i 1)
> (unsafe-fx+ count 1) (unsafe-fx+ quadrat steigung) (unsafe-fx+ steigung 2)))
> (else (loop (unsafe-fx+ 1 i) count (unsafe-fx+ quadrat steigung)
> (unsafe-fx+ steigung 2)))))
> (loop 2 0 4 5))
>
> (acht-teiler 36)
>
> (: achter (-> Fixnum Fixnum))
> (define (achter (n : Fixnum))
> (: loop (-> Fixnum Fixnum Fixnum))
> (define (loop (i : Fixnum) (count : Fixnum))
> (cond ((unsafe-fx= i n) count)
> ((acht-teiler i) (loop (unsafe-fx+ i 1) (unsafe-fx+ count 1)))
> (else (loop (unsafe-fx+ i 1) count))))
> (loop 2 0))
>
> (time (achter 1000000))
> ; for 100 = 24, 30, 40, 42, 54, 56, 66, 70, 78 and 88
> ; f(100) = 10, f(1000) = 180 and f(10e6) = 224427
>
> for java:
>
> import java.util.concurrent.Executor;
> import java.util.concurrent.ExecutorService;
> import java.util.concurrent.Executors;
> import java.util.concurrent.TimeUnit;
>
> public class EightDivs implements Runnable{
>
> public static Object lock = new Object();
> public static long count = 0;
>
> private long low;
> private long high;
>
> public EightDivs(long low, long high){
> this.low = low;
> this.high = high;
> }
>
> public boolean hasEightDivsExact(long a){
> int divs = 0;
> for(long i =1;i<=a;i++){
> if(a % i == 0){
> divs++;
> }
> }
> return divs == 8;
> }
>
> public boolean hasEightDivs(long a){
> int divs = 0;
> for(long i = 2; i*i <= a && divs < 4;i++){
> if(a % i == 0){
> divs++;
> if (i*i == a && divs >= 3){
> return false;
> }
> }
> }
> return divs == 3;
> }
>
> public static void main(String[] args) throws InterruptedException {
> ExecutorService ex = Executors.newFixedThreadPool(4);
> long old = 1;
> long start = System.currentTimeMillis();
> // for(long i = 0L; i<= 1000_000L;i+=100_00){
> // ex.execute(new EightDivs(old, i));
> //// System.out.println(old +" low " + i + " high");
> // old = i;
> // }
> // ex.shutdown();
> // ex.awaitTermination(300, TimeUnit.SECONDS);
> new EightDivs(1, 1000_000).run();
> long end = System.currentTimeMillis();
> System.out.println((end-start)/1000d+" Seconds");
> // new EightDivs(1, 1000).hasEightDivs(24);
>
> System.out.println(count);
> }
>
> @Override
> public void run() {
> for(long i = low;i<high;i++){
> if(hasEightDivs(i)){
> // System.out.println(i);
> synchronized (lock) {
> count++;
> }
> }
> }
> System.out.println(low +" low " + high + " high done");
> }
>
> }
>
>
> --END CODE
>
> java code runs in 4.5 seconds
> racket code takes 12.5 seconds to complete (in cli-mode)
>
> i typed racket and used unsafe operations. some perfomance hints from the
> guide don't seem to apply since i already tyyped racket.
> the optimization coach hints to use define-inline but it seems to be
> available only in non-typed-raket.
>
> what can i do to speed things up (except better algorithms?)
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