## digitalmars.D.announce - xoroshiro128+ random number generator

Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:
```Spotted this reddit post the other day:

... and it reminded me that I've been meaning for some time to
follow up on the interesting RNG designs by Sebastiano Vigna and
colleagues.  Since I had a free moment, I thought I'd knock up a
D port of the public-domain C reference code available here:
http://xorshift.di.unimi.it/xoroshiro128plus.c

It's a first draft and obviously needs documentation, tests, etc.
before I submit it to Phobos, but I thought I'd throw it out here
if anyone wants to play with it and/or comment.  I'll also try to
follow up in the next days with an xorshift1024* implementation,
which should be similarly straightforward.

Code follows -- enjoy! :-)

struct Xoroshiro128plus
{
public:
enum bool isUniformRandom = true;

/// Range primitives
enum bool empty = false;

/// ditto
ulong front()  property  safe const nothrow pure
{
return s[0] + s[1];
}

/// ditto
void popFront()  safe nothrow pure
{
immutable ulong s1 = s[1] ^ s[0];
s[0] = rotateLeft(s[0], 55) ^ s1 ^ (s1 << 14);
s[1] = rotateLeft(s1, 36);
}

void seed(ulong s0, ulong s1)  safe nothrow pure
in
{
// seeds are not both 0
assert(!(!s0 && !s1));
}
body
{
s[0] = s0;
s[1] = s1;
}

void seed(ulong[2] s01)  safe nothrow pure
in
{
// seeds are not both 0
assert(!(!s01[0] && !s01[1]));
}
body
{
s[] = s01[];
}

private:
ulong[2] s;

static ulong rotateLeft(ulong x, int k)  safe nothrow pure
in
{
assert(k <= 64);
}
body
{
return (x << k) | (x >> (64 - k));
}
}
```
Apr 29 2016
=?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
```On Friday, 29 April 2016 at 21:40:49 UTC, Joseph Rushton Wakeling
wrote:
Spotted this reddit post the other day:

nogc :)
```
Apr 30 2016
Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:
```On Saturday, 30 April 2016 at 08:54:39 UTC, Nordlöw wrote:
On Friday, 29 April 2016 at 21:40:49 UTC, Joseph Rushton
Wakeling wrote:
Spotted this reddit post the other day:

nogc :)

Hah, nicely spotted :-)
```
Apr 30 2016
Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:
```On Saturday, 30 April 2016 at 11:04:14 UTC, Joseph Rushton
Wakeling wrote:
On Saturday, 30 April 2016 at 08:54:39 UTC, Nordlöw wrote:
On Friday, 29 April 2016 at 21:40:49 UTC, Joseph Rushton
Wakeling wrote:
Spotted this reddit post the other day:

nogc :)

Hah, nicely spotted :-)

More importantly, the public fields of this generator should
include:

enum ulong min = ulong.min;

enum ulong max = ulong.max;

... otherwise it won't work with `uniform` or anything that
depends on it.
```
Apr 30 2016