this post was submitted on 02 Feb 2024
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Programming

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Hi all,

Some time ago I've been thinking about a programming challenge that's not simply another HackerRank style algorithm task and came up with something that I myself had a lot of fun solving. It goes like this:

We have a well known function (as in I didn't come up with it):

 function xoshiro128ss(a, b, c, d) {
                return function() {
                    var t = b << 9, r = b * 5; r = (r << 7 | r >>> 25) * 9;
                    c ^= a; 
                    d ^= b;
                    b ^= c; 
                    a ^= d; 
                    c ^= t;
                    d = d << 11 | d >>> 21;
                    
                    return (r >>> 0) / 4294967296;
                }
            }  

We initialize it with 4 random parameters a,b,c,d (that I selected) :

  let rnd = xoshiro128ss(a, b, c, d);

and we do:

  let rand1 = rnd();
  let rand2 = rnd();
  let rand3 = rnd();
  let rand4 = rnd();

Knowing that:

rand1 == 0.38203435111790895
rand2 == 0.5012949781958014
rand3 == 0.5278898433316499
rand4 == 0.5114834443666041

What are the values of a,b,c and d?

I was wandering if it's possible to figure it out and couldn't stop trying until I did. It was an interesting journey and I learned some new things along the way Maybe someone else here will also have fun with it. As for prizes, I don't know... whoever posts the right answer first gets an upvote and eternal fame.

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[–] ExLisper@linux.community 3 points 9 months ago

a >= 0, b >= 0, c >= 0, d >= 0

I think that's the issue, in the second possible solution one of the parameters is negative :)

This looks great, I didn't even know it's possible to solve it this way. I'm glad someone dedicated some time to it. Let's see if anyone will try solving it in other way.