Xorshift_star.md

Pseudo-random numbers/Xorshift star

Raku does not have unsigned Integers at this time (Integers are arbitrary sized) so use explicit bit masks during bitwise operations. All constants are encapsulated inside the class.

class Xorshift-star {
    has $!state;

    submethod BUILD ( Int :$seed where * > 0 = 1 ) { $!state = $seed }

    method next-int {
        $!state +^= $!state +> 12;
        $!state +^= $!state +< 25 +& (2⁶⁴ - 1);
        $!state +^= $!state +> 27;
        ($!state * 0x2545F4914F6CDD1D) +> 32 +& (2³² - 1)
    }

    method next-rat { self.next-int / 2³² }
}

# Test next-int
say 'Seed: 1234567; first five Int values';
my $rng = Xorshift-star.new( :seed(1234567) );
.say for $rng.next-int xx 5;


# Test next-rat (since these are rational numbers by default)
say "\nSeed: 987654321; first 1e5 Rat values histogram";
$rng = Xorshift-star.new( :seed(987654321) );
say ( ($rng.next-rat * 5).floor xx 100_000 ).Bag;


# Test with default seed
say "\nSeed: default; first five Int values";
$rng = Xorshift-star.new;
.say for $rng.next-int xx 5;

Output:

Seed: 1234567; first five Int values
3540625527
2750739987
4037983143
1993361440
3809424708

Seed: 987654321; first 1e5 Rat values histogram
Bag(0(20103), 1(19922), 2(19937), 3(20031), 4(20007))

Seed: default; first five Int values
1206177355
2882512552
3117485455
1303648416
241277360